20X100 25x100 Binocular
halfro
Szaki
"halfro" <halfr...@comcast.net> wrote in message news:7fc2c.52145$ko6.402486@attbi_s02...
Ioannis
news:7fc2c.52145$ko6.402486@attbi_s02...
Apogee. It's probably the only company that has 20x100 so inexpensive. Here
are some quick thoughts:
I got mine yesterday. They are impossible to look through without a tripod.
First. Second, I do notice some intense violet chromatic aberation, during
daytime use, but the aberation is not much more than on my 11x80 Japanese
Chinons. It's to be expected with such large lenses.
For nightime, they are a blast. I tested them a little yesterday, outside my
balcony. I could see at night, under almost black skies the mast of an
antenna, 20 km's away. They focus nicely, and they are a sturdy
construction. I do detect minor spectra of the street lights, particularly
mercury lights around the edges, but again, it's not worse than with my
11x80 Chinons. The chromatic aberation is more intense around the edges, of
course.
I haven't noticed any substancial spherical aberation around the edges.
Images are quite sharp and flat to the edge.
I will have a chance to test drive them in the Antiparos Greek isle, around
Easter, so till then I cannot offer any substancial advice, but they seem
quite a respectable pair. Ok, they are not Miyachi's, but i'd say they are
the best value for such a price. And their normal price is actually $350, so
they are not really that inexpensive. Apogee has a special on them.
I am so far very very happy with them.
--
Ioannis Galidakis
http://users.forthnet.gr/ath/jgal/
------------------------------------------
Eventually, _everything_ is understandable
JBortle
pair of the 20x100's. Collimation is a little off (as I'm hearing is quite
common with these particular binoculars) but the images can be "fused" without
difficulty. However, and very much to my surprise and general disappointment,
they do not appear to show diffuse celestial objects (like comets, my special
interest) any better than do my higher quality pair of 15x70's. As someone who
has owned a pair of WWII Japanese 20x120's for many years, I have to say the
newer examples don't hold a candle to the older instrument with regard to what
can be seen with them.
John Bortle
tony hoffman
(http://www.bigbinoculars.com/22100.htm), about which I have heard a lot of
good things. They cost slightly more ($395); hopefully, they're worth it.
--Tony
Craig Levine
I have the Oberwwerk 20x80' "Standard" model. It can be bumped out of
collimation fairly easily, but collimating it is a breeze. There are
screws under the rubber armour that you adjust to re-collimate. Images
are good through them, though there is an expected amount of chromatic
abberration. The long eye-relief and Panoptic-like AFOV makes them
very comfortable to use with glasses. For the $$, they're a good
value.
Cheers,
- Craig
Craig Levine
Observing Chairman
RASC, Halifax Centre
www.halifax.rasc.ca
Ioannis
news:i9fk40l4kei2v3lbp...@4ax.com...
[snip]
> I have the Oberwwerk 20x80' "Standard" model. It can be bumped out of
> collimation fairly easily, but collimating it is a breeze. There are
> screws under the rubber armour that you adjust to re-collimate. Images
> are good through them, though there is an expected amount of chromatic
> abberration. The long eye-relief and Panoptic-like AFOV makes them
> very comfortable to use with glasses. For the $$, they're a good
> value.
Looking at the 22x100 Oberwerk picts, and my 20x100 Apogee which sits on my
living room, the overall design appears identical. Same retaining rings,
same lens cells, both have BaK4 prisms, same tripod support, same tube
sizes, same porro folding and similar EP endings. The only thing that
differs seems to be the tube coating finish.
The Apogee also has 2-3 tiny screws around each porro prism which can be
used to re-collimate the images. I imagine this is a standard design, which
has been picked up by various companies in order to mass produce 20x100
giant binos. There is undoubtedly some small variation between the different
designs and brands, but overall, I wouldn't expect any major differences,
qualitywise for this price.
The Apogee were just a tad out of collimation when I first looked at them,
but the difference was so slight that my brain adjusted immediatelly upon
adjusting the Interpupilary Distance a bit. Had it been worse, I would have
fiddled with the little screws, but there was no need for that.
I don't see any reason why one would want to pay the extra $150 for the
Oberwerk, unless there exists some substancial optical difference which I am
not aware of and affects viewing quality.
> Cheers,
>
> - Craig
>
> Craig Levine
> Observing Chairman
> RASC, Halifax Centre
> www.halifax.rasc.ca
edz
I aslo have the 20x80 standards. they have remained collimated since
the day I got them. I've never had to adjust them. same goes for my
15x70/'03 models Oberwerks. I've never had to collimate either pair.
They both have a minor error of about 1 arcmin. No need to adjust for
that. Both have very good optics.
Some of the brands do not come fully multi-coated. Look for and
demand that feature. It does make a considerable difference. I've
tested the same binocular with and without FMC. I can attest to the
improvement.
Some models have a very short right diopter range and will not
accomodate a poor right eye nearsighted perscription unless galsses
are always worn.
The size binocular you are considering will require a very substantial
mount. A tripod on the order of a Bogen 3221 w/ 501 head or with a
substantial UA mount, something more than the Unimount Light Deluxe.
You will pay more for than mount than you will for the binoculars and
it is a necessity due to the weight of the binocs. On the other hand,
the 20x80 standards can be mounted on a Bogen 3211 w/3130 head, a
setup less costly than the binocs. Although they do much better on a
UA Unimount Light Basic.
edz
Shneor Sherman
> Easter, so till then I cannot offer any substancial advice, but they seem
> quite a respectable pair. Ok, they are not Miyachi's, but i'd say they are
> the best value for such a price. And their normal price is actually $350, so
> they are not really that inexpensive. Apogee has a special on them.
>
> I am so far very very happy with them.
I have a pair of 25x100s (Burgess), which are superb and provide
breathtaking views. I did not take them with me to Paros and
Antiparos, where I spent a week last October. I brought along a 90mm
ETX with a photo tripod. You really need a sturdy parallelogram mount
to use the 25x100s to advantage.
Clear skies,
Shneor Sherman
Shneor Sherman
Depends on who you get them from. Burgess star tests every pair and
rejects those that don't make the grade. I have a pair of his 25x100
rejects (eyepiece coatings are only Magnesium flouride, not
mulicoated) and I have had and shared spectacular views of the Helix,
the Veil (with filters), M42, M27, M51, M81/82, Markarian's Chain in a
single field of view, etc. etc.
Clear skies,
Shneor Sherman
Chris1011
a
> pair of the 20x100's. Collimation is a little off (as I'm hearing is quite
> common with these particular binoculars) but the images can be "fused"
without
> difficulty. However, and very much to my surprise and general disappointment,
> they do not appear to show diffuse celestial objects (like comets, my special
> interest) any better than do my higher quality pair of 15x70's.
Most people don't realize how much internal vignetting there is with some of
these Chinese binoculars. The prisms are typically too small, even though they
may use Bak4. They use round internal field stops so that it appears that the
exit pupil is fully illuminated when you look into the eyepiece end. I have
seen some that are over 30% vignetted. Yes, they give good star tests, but it
is because they are internally stopped down. Furthermore, to save money, a lot
of these binos do not have anti-reflection coatings on the internal prism
faces, or on the eyepiece field lenses. I have a pair of multi-coated 10 x 45
Minolta binos (not cheap unfortunately) that are every bit as bright as most of
the cheap 70 - 80mm Chinese binos.
You can easily see whether your binos are fully illuminated and not stopped
down. Place your eye at the very edge of the front element and look down into
the prism. If you can see the entire eyepiece exit pupil from one edge to the
other, it is fully illuminated to the full aperture of the front element. If
you can see only part of the exit pupil, it is internally vignetted to some
degree.
RC
lal_truckee
> You can easily see whether your binos are fully illuminated and not stopped
> down. Place your eye at the very edge of the front element and look down into
> the prism. If you can see the entire eyepiece exit pupil from one edge to the
> other, it is fully illuminated to the full aperture of the front element. If
> you can see only part of the exit pupil, it is internally vignetted to some
> degree.
Thanks - this kind of information is directly useful.
Ioannis
news:404CB955...@yahoo.com...
Ditto. I will check my 20x100 Apogee as such, in two weeks. I just returned
to Crete for work, so the pair is safely tucked in its case in my wife's
livingroom, boobytrapped.
I did have a chance to check out M42 though under yesterday's moon and
highly polluted skies from Athens, and it appears slighly brighter than with
my Chinon 11x80. I could clearly discern the dark spike going to the
Trapezium using direct vision, the Trapezium resolves into 3, (perhaps 4, I
couldn't really tell) and the flower shape was clearly visible. With my
11x80's the nebula boundaries are not so clear, unless the sky is very dark.
I will see if I can mount both the 11x80 Chinons and the 20x100 Apogee on
the same tripod and create a comparison report later on a few known objects,
although I doubt I will be successful, as the weight of both will strain my
tripod a bit and moving both pairs will require a crane.
Happy observing!
Bill Meyers
70s are a bit vignetted.
Bill Meyers
edz
As Bill replies, on this basis, I find almost every binocular I own
would fit you criteria for vignetted. I don't believe this is an
accurate test. This would indicate both my 10x70 and 16x70 Fujinons
are about 30% to 40% vignetted. So would my Pentax, my Swift,
Minolta, Nikon, Oberwerk and Orion. That is not correct. In fact I
own about 15 binoculars. I have not found a single one that would
pass this test.
I have seen the description of this test written by Roland Christen
(almost word for word as described above). I think there needs to be
some explanation. In every case, the baffles will prevent you from
seeing the full edge of the prism. However in no case was the exit
pupil smaller than the aperture magnification would indicate. To me,
that means the full aperture is in use.
You want to know if your binocs are vignetted, measure your exit
pupils.
edz
Brian Tung
> As Bill replies, on this basis, I find almost every binocular I own
> would fit you criteria for vignetted. I don't believe this is an
> accurate test. This would indicate both my 10x70 and 16x70 Fujinons
> are about 30% to 40% vignetted. So would my Pentax, my Swift,
> Minolta, Nikon, Oberwerk and Orion. That is not correct. In fact I
> own about 15 binoculars. I have not found a single one that would
> pass this test.
>
> I have seen the description of this test written by Roland Christen
> (almost word for word as described above). I think there needs to be
> some explanation. In every case, the baffles will prevent you from
> seeing the full edge of the prism. However in no case was the exit
> pupil smaller than the aperture magnification would indicate. To me,
> that means the full aperture is in use.
>
> You want to know if your binocs are vignetted, measure your exit
> pupils.
Uh, wouldn't that just tell you whether or not the *center* of field
was vignetted? That is, wouldn't it only tell you that your fully
illuminated field was non-zero?
The point of putting your eye at the edge is presumably to evaluate
the degree of vignetting at an extreme off-axis angle (in AFOV). That
seems like the right test to me. It *is* hard to satisfy. I can see
legitimate reasons for not making sure it's satisfied, just as I can
see legitimate reasons for not making sure the entire field stop of
a 41 Pan in a Newtonian, for instance. Just because it's a legitimate
thing to do does not mean it doesn't happen, though.
Binoculars are almost exclusively visual instruments. I'd be more
concerned about correcting the edge of the field than I would be about
making sure that edge was fully illuminated.
Brian Tung <br...@isi.edu>
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt
Chris1011
the degree of vignetting at an extreme off-axis angle (in AFOV).>>
The point of putting your eye at the edge of the front aperture is that you can
very quickly evaluate whether the center and BOTH the edges of the exit pupil
are fully illuminated. If that is true, then the entire field is fully
illuminated.
If you can see only one edge and center from the periphery of the front
aperture, then the field is only partially illuminated by the full front
aperture.
If you cannot see the CENTER of the exit pupil from the edge of the front lens,
but can see one edge, then the binos are NOT fully illuminated in the center of
the field. They are somewhat vignetted. In this case, to determine the actual
aperture of the binos in the center of the field, just place a series of
cutouts with different apertures over the front until you find the one which
allows you to just begin to see the center of the exit pupil. That would be the
aperture that contributes to the image in the center of your eyepiece field.
Continue with smaller apertures until you can see the entire exit pupil from
the edge of the aperture. That would be the size of the front lens that
illuminates the edge of your eyepiece field.
Sounds complicated but really isn't.
Roland Christen
Ioannis
news:20040329121640...@mb-m29.aol.com...
Thanks for the explanation Roland. I can see the center of the exit pupil on
my Apogee 20x100, along with one side of the exit pupil, but not the side
corresponding to the side from which I am looking down to, which according
to your explanation means that the center is fully illuminated but the edges
are not.
The exit pupil from the edge looks exactly like Venus' shape at its current
stage.
The question though is, why would one manufacture the optics as such, if one
could simply use a smaller full apperture unvignetted?
It doesn't make much sense to me. Any further explanations?
> Roland Christen
Chris1011
could simply use a smaller full apperture unvignetted?>>
You get more money for a supposedly "larger" front aperture, regardless if it's
fully used or not.
Roland Christen
Brian Tung
> The point of putting your eye at the edge of the front aperture is that
> you can very quickly evaluate whether the center and BOTH the edges of
> the exit pupil are fully illuminated. If that is true, then the entire
> field is fully illuminated.
Oops, my mistake--I mistook "front lens" for "eyepiece." The idea, then,
is that if the edge of the objective can see the center of the exit pupil
(which is delineated by the field stop?), then the center can see the
entire objective, and therefore the center is fully illuminated.
Correspondingly, if the edge of the objective can see the entire exit
pupil, then the entire exit pupil can see the entire objective, and the
entire field is fully illuminated.
Is that so?
Paul S. Walsh
http://www.nwlink.com/~filmdos/binovign.gif
-Paul S. Walsh
"Chris1011" <chri...@aol.com> wrote in message
news:20040329121640...@mb-m29.aol.com...
>
> If you can see only one edge and center from the periphery of the front
> aperture, then the field is only partially illuminated by the full front
> aperture.
[etc, etc...]
>
> Roland Christen
Ioannis
news:106gs7j...@corp.supernews.com...
What's the little red circle? I can see the center of the exit opening, so I
assume that I can see the red circle, but I am not sure what the difference
between the green and red circles is.
> -Paul S. Walsh
Brian Tung
> What's the little red circle? I can see the center of the exit opening, so I
> assume that I can see the red circle, but I am not sure what the difference
> between the green and red circles is.
I only see the field stop (and a sequence of baffles). As I guessed
before, if you can see the entire field stop from the edge of the front
objective, the entire field is fully illuminated. If you can see the
center of field from the edge of the front objective, then the center
of field is fully illuminated. I *think* that's the right interpretation
of the test.
In the case of my 10x30 Canon IS's, it appears the center is fully
illuminated (and so is a small part of the field surrounding the center),
but the edge is not. That effect is noticeable when using the binoculars
in the usual way, but it's hardly distracting.
Paul S. Walsh
eyelens (the lens closest to the eye when viewing) and I used Green to
represent the pupil of the human eye peering into the eyelens and centered
on that lens - but I also could simply be misunderstanding what Roland has
been describing.
-Paul S. Walsh
"Ioannis" <morp...@olympus.mons> wrote in message
news:10805873...@athnrd02.forthnet.gr...
Rob J.
discontinued, as I didn't see them on today's webbsite. Nevertheless,
they are alot of fun, poular at observing sessions with other
astronomers and provide some remarkable views.
Like other Chinese binoc's, they can show a tinge of false color
around very bright objects such as the moon. However, the stars appear
just as they do in my 12" scope, with beautiful color.
They are prone to going out of colimnation. I check them before each
session and I carry a small screw driver in their case. The adjustment
takes about one minute to perform. Also, they don't their hold focus
as well as they should. If you swing them from one direction to
another, it's likely that you'll have to refocus.
But I play with the focus for each individual object anyway. Hey,
what else have I got to do?
And the right eye piece focuser is odd. Sometimes it needs
adjustment to the right and other days it's more to the left!
I got the UA mount. It's great! It cost more than the binoc's, but it
will be with me for my lifetime. I'm glad I didn't cheap out on the
mount. It makes the whole experience much more enjoyable and
comfortable. Just lay back in your recliner and pull the binoc's to
your eyes.
Some people aren't interested in big binocs because a mount is
required. But none of us would ever buy a telescope without a mount.
Many amateurs are missing out on some amazing views. You
Incidently, I use my binoc's in my family room. I clean my glass
skylight and setup below. The skylight provides a narrow view, and it
does give off double images of bright objects, like the planets, but
it sure beats going outside in to the N. Y. winter. M42, for example,
looks almost the same as it does when viewed outdoors, especially when
its directly centered in the skylight.
Of course, higher powered instruments wouldn't perform as well
under these conditions.
Pete Rasmussen
>>>The point of putting your eye at the edge is presumably to evaluate
>the degree of vignetting at an extreme off-axis angle (in AFOV).>>
Agreed. Then if vignetted, a person "may" would be able to see a
lesser bright periferal area inside the instrument exit pupil circle
as viewed a few inches away from the eyepieces, while the entrance
aperture is evenly illuminated, no?
Pete
Pete Rasmussen
Hi, somewhere in this thread you mentioned the collimation of your
pair of 20x100 was slightly out, yet your eyes could still fuse the
images. If you tweak the collimation adjustment a little, your eyes
will be allowed to become more relaxed to view better and more astro
details :)
Pete
Chris1011
>lesser bright periferal area inside the instrument exit pupil circle
>as viewed a few inches away from the eyepieces, while the entrance
>aperture is evenly illuminated, no?
It doesn't work that way. The exit pupil may very well be perfectly round when
viewed several inches away at the eyepiece end, yet can be severely vignetted
anyway.
A person can see if the edges of the field are vignetted by viewing the exit
pupil at the eyepiece end at an extreme angle. If the edge is vignetted, then
the exit pupil will look D shaped.
Roland Christen
edz
> Uh, wouldn't that just tell you whether or not the *center* of field
> was vignetted? That is, wouldn't it only tell you that your fully
> illuminated field was non-zero?
That's correct.
Momentary case of brain wander. The exit pupil wouldn't get smaller
AND it would be extreemly difficult to see light drop off in the exit
pupil.
But I still must mention again, I have 16 pairs of binoculars,
Minoltas, Orions, Swifts, Nikons, Oberwerks and Fujinons. When
holding my eye at the edge and looking into the barrel towards the
prisms, not a single pair can see the entire edge of the prism field
stop. Every single one is cut off by the baffles. And almost all of
them are cut off by about 30% to 40%.
edz
edz
one is cut off by the baffles. Most are cut off about 30% to 40% all
around.
If 30% of the edge is cut of from the center of the exit pupil all
around, then the center is illuminated by only 40% of the objective.
I just can't see that kind of light drop off in the view. But maybe I
just need to quantify it.
I have 16 different pair of binoculars. Minolta, Swift, Nikon, Orion,
Pentax, Oberwerk and Fujinon, some of the most respected binocular
astronomy models on the market. Every single pair I looked into, the
baffle cut off about 30% of the edge of the prism opening.
This seems a reasonable proposal and it makes sense that it is missing
some of the light, but i just don't see the light dropping off that
much. I have measured a drop in limiting mag from center to edge in
some models, but it seems to me that it is mostly driven by edge
distortions growing more prominent at 60%, 70% or more out from
center. In the worst case I see a drop of about 0.5 mag from center
to about 70% to 80% out.
I will be checking this and taking notes. I'd like to see if I can
determine how much light is being lost from the outer edges and what
affect it is having. Personally, I don't see much affect. Either
that or differences that I do see I'm attributing to something else.
Whatever the case may be, thanks for this heads up.
edz
edz
assuming the baffles cut off 30% of the object from providing light to
the exit pupil, and
every point in the exit pupil is lit from every point (unobstructed)
in the objective, then
the light fall off at any point in the exit pupil is only that of the
obstructed aperture on the same side.
If viewed from the objective end the baffel seems to be cuttiing of
30% of the objective light from hitting the same side of the prism,
then the exit pupil towards the edges is still 70% illuminated. These
drop offs in light towards the edges of the exit pupil may not be as
easy to see as I thought. Especially if I begin to take more accurate
measures and find only 20% of the objective light is cut off at the
outer edge of the exit pupil.
This may begin to correlate very well with the drop off of limiting
magnitude towards the outer edges. A good test will need a binocular
that is very well corrected for distortions as far out as possible.
Oberwerk 15x70 and 20x80 standards, Fujinon 16x70 and Pentax 16x60 are
all pretty well corrected at least to 80%-90% out from center, out
past the expected area of light drop off in the image if baffles cut
in at 30%. With distortions nearly eliminated, most of the limiting
magnitude drop may be attributed to light cut off. Does that seem a
reasonable presumption?
edz
J. Thomas Jeffrey
> some company are advertising this type of binoculars for $199 to $259.00
> are this any good???
> comments would be appreciated, while these binocs are not expensive, I
> do not want to throw
> money away.
> --
According to Bigbioculars.com the 20X80 binoculars are being
discontinued. I just bought the 20x90 binoculars from them yesterday.
They still have a few of the 20x80's left.
Ioannis
Ο "Pete Rasmussen" <eye_...@arkansas.net> έγραψε στο μήνυμα
news:ikuh60t3tf41ujtsl...@4ax.com...
Hi Pete, yeah I know.
I didn't get a chance to fiddle with the little screws last week. I will
probably do it next week sometime.
I had my girlfriend check this. She reported that she could see the moon as
a single image, as well as daytime images as single images, but stars as
double.
Which means that the pair is ever so slightly out, that if the images are
bright enough the brain fuses them.
> Pete
kbus...@woh.rr.com
20x80's- the LW, Standard, and Deluxe. The 20x80 Deluxe was discontinued as
of 12/31/03, replaced by the 20x90. The 20x80LW and 20x80 Standard remain
in the current product line.
Kevin Busarow
Oberwerk Corp.
"J. Thomas Jeffrey" <Ranger...@netscape.net> wrote in message
news:b6ae4347.04033...@posting.google.com...
edz
viewing from the very edge of the objective end into the binocular, I
was able to easily observe the light path is obstructed by the baffles
in every binocular I own. I measured each binocular by how much of
the light path is obstructed. For example, if the light path were
obstructed (vignetted) 50%, I would be able to line up my line of
sight from the edge of the objective past the edge of the baffle and
see exactly to the middle of the exit pupil. If it were more than
50% vignetted, as I found, less than half the exit pupil will be seen.
In no instance was I able to see even half of the exit pupil. These
are not precise measures, however they were observed several times
each and both lenses were checked not only side to side but top to
bottom.
These are the OBSTRUCTED measurements I observed.
Minolta Standard 7x35 60%
Minoltas Activa 7x35 50%
Swift Ultralite 8x42 80%
Pentax PCF III 12x50 70%
Pentax PCF V 16x60 70%
Oberwerk 15x70 80%
Fujinon FMT SX 10x70 70%
Fujinon FMT SX 16x70 70%
Oberwerk Deluxe 20x80 70%
Oberwerk Standard 20x80 80%
Oberwerk BT100 100%
Needless to say, I'm stunned. I need to sit back and digest this
before I make any other comments on this. I am so curious to see what
types of readings anyone else is getting.
edz
Alan French
news:90c65221.04033...@posting.google.com...
Ed,
Most optical systems do not fully illuminate the edge of the field, and some
loss of illumination as you approach the field stop is common and generally
goes without notice. If you want full illumination across the entire field,
you are going to pay a price - in terms of cost, bulk, and weight. In
normal use, had you ever noticed a lack of brightness at the edge of the
field in a pair of binoculars (no fair looking now, you're probably
expecting to see it)?
Clear skies, Alan
Ioannis
news:90c65221.04033...@posting.google.com...
[snip]
> These are the OBSTRUCTED measurements I observed.
>
> Oberwerk BT100 100%
What the...?
So the Oberwerk contain metal baffle plates that shield the main lens off
completely?
Can you see through them at all?
> Needless to say, I'm stunned. I need to sit back and digest this
> before I make any other comments on this. I am so curious to see what
> types of readings anyone else is getting.
>
> edz
Anton Jopko
In my pentax pf 80 ed spotting scope and 10.5 mm eyepiece, the edge of the exit
pupil gets about 75% illuminated. the center is at least fully illuminated.
anton
edz
> So the Oberwerk contain metal baffle plates that shield the main lens off
> completely?
> Can you see through them at all?
Oh yes, you can see quite well through the BT100. Actually the BT100
provides binocular views like none I've ever seen before. Read my
review over on the Cloudy Nights Binocular Forum. Within the first
few weeks, I have been resolving clusters to the core, splitting
doubles as close as 7 arcseconds, reaching BLM as deep as mag12 at 60x
and seeing for the first time, the Merope nebula and a portion of the
Rosette. However, in the grand scheme of things it may appear it is
operating with maybe only a 85mm-90mm objective area. I believe Barry
Simon pointed something similar out some time ago about his findings
in the Miyauchi line.
I fully understand the baffels are there to control aberrations, but
to what extent. This revelation should go a long way in explaining
why some terrestrial users observe a brighter image in one model over
the other. Brightness of image may have a lot more to do with
vignetted exit pupil than to do with overall size of exit pupil. A
5mm exit pupil that is vignetted 80% will have far less peripheral
light than a 4mm exit pupil that is vignetted only 50%.
edz
Brian Tung
> Oh yes, you can see quite well through the BT100.
No, I think you've misunderstood Ioannis's comment. He thinks (and I
agree) that your 100 percent figure doesn't make sense. Can you really
see nothing when looking through the objective end of your telescope
at the edge of the objective?
edz
I took his comment as a jest.
When you perform this test, viewing from the edge of the objective
into the prism field stop, as I have indicated above, nearly every
binocular shows 70% to 80% of the prism field stop is hidden. In the
BT100, if you view from the edge of the objective NONE of the prism
field stop is visible. I used a small scale and performed the same
test and found I needed to move my eye in along the objective a
little less than 10mm before I could see any part of the prism field
stop. That would indicate the outer 5-10mm of the objective is not
providing ANY light to the prism. Hence, my posted value, when
viewing from the edge of the objective, 100% of the prism is
obstructed.
If you view into the objective from the very edge and see 70% of the
prism field stop circle is obstructed, that means even the center of
the exit pupil is NOT fully illuminated. In order for the center of
the exit pupil to be 100% illuminated by every light ray from the
objective, the center of the field stop must be visible from every
point on the objective lens. Only one out of the twelve binoculars I
looked at met that test, and it just barely.
What I have not yet determined is this. I do not know the effective
aperture of 100% illumination. Roland points out, and this seems so
clear now, it can be found by placing progressively smaller masks over
the objective and repeating the test until the entire prism field stop
can be seen all the way around from every edge.
Rather than make so many different sized masks, I believe it could
also be found by securing a measuring scale across the center of the
objective end and noting with a piece of sticky tape the point at
which 100% of the field stop can be seen. Check both sides and the
distance between the two pieces of tape would be the effctive aperture
of 100% illumination.
edz
edz
objective looking in, I observed the exit pupils. I should have said
I cannot see the full exit pupil in any one.
I can see the full edge of the prism field stop in almost every
binocular. i cannot see the full exit pupil.
edz
ezar...@gilbaneco.com (edz) wrote in message news:<90c65221.04033...@posting.google.com>...
edz
again the whole validity of trying to observe the exit pupil through
the objective to assess how much vignette might be present. Here's
why.
I went back to read Roland's original statement, this is what he says.
"You can easily see whether your binos are fully illuminated and not
stopped down. Place your eye at the very edge of the front element and
look down into the prism. If you can see the entire eyepiece exit
pupil from one edge to the other, it is fully illuminated to the full
aperture of the front element. If you can see only part of the exit
pupil, it is internally vignetted to some degree."
First, I observed the exit pupil from the edge of the objective. The
first time I looked into the binoculars and recorded this info, I
actually recorded how much I could see of the exit pupils. I don't
think that is accurately showing light blocked from the objective.
This is what I did the second time around. I did the exact same view
from the edge of the objective, but this time I observed the first
prism surface. I wanted to see if the baffles were cutting off light
before it reached the prisms field stop.
To check if the baffles vignette, it is not the exit pupil we should
be looking at. It is the prism field stop. If you can't see the edge
of the prism field stop, the baffle is causing vignette.
In order to see how much of the objective light is missing the prism
field stop, you must look from the edge of the objective, past the
edges of the baffles, and observe the first prism. You can see this
prism surface if you allow some light to shine down into the
binoculars. When you do this you can see the edges of the baffles
hide none at all or only a very small portion of the prism edge. In
10 out of 12 binoculars the entire prism field stop is seen 100%. In
the others the baffles were hiding a very small portion of the prism
field stop. In both cases, they indicated a potential obstruction of
the full aperture by about 10%.
So here is where I have a real hard problem with this exit pupil
method. In almost every binocular, I can see 100% of the prism field
stop. But in every one of these same binoculars, usually 70% or 80%
of the exit pupil is not seen. These readings do not correlate at
all.
If the baffles are not cutting off any of the light, and an
observation of the exit pupil seems to indicate ~70% of the exit pupil
is not illuminated from the edge of the objective, then all the cut
off would be due to the prisms or the field stop. I don't buy that
result. In order for that to happen, the prisms would have to be so
small, they would look like they belonged in a toy binocular. I can
tell you the prisms in my Fujinons are quite large. They are NOT
cutting off 70% of the light to the exit pupils.
Even though it seemed clear to me before, something doesn't wash here,
and I'm now inclined to believe this method of assessment by observing
exit pupil is flawed. You are going to have a hard time to convince
me that my Fujinons are not even fully illuminated at the center of
the exit pupil as this assessment would indicate if it is true. Went
from embracing it to not buying it in one day.
edz
ezar...@gilbaneco.com (edz) wrote in message news:<90c65221.04033...@posting.google.com>...
edz
> again the whole validity of trying to observe the exit pupil through
> the objective to assess how much vignette might be present. Here's
> why.
>
This morning I took apart one pair of binoculars to test out the
validity of this method of assessing vignette.
Orion Ultraview 10x50,
Exit pupil observed through objective end = 70% obstructed
Prism field stop observed through objective = on edge (to close to
tell, say 5% obstructed)
The mechanics of the light path are simple, the cone is constant to a
zero point at the focal length. The cone must pass through a hole to
enter the prism. If the hole is big enough, the prism is big enough.
I used vernier calipers, measured light path, distance objective to
prism, lens thickness, calculated focal length thru prisms as a result
of refractive index in prisms, determined focal length of objectives.
(For a complete explanation of how to determine focal length in
binoculars, see my old post over on CN binoc forum).
The focal length of the objective calcs to be 192mm.
The prism face is 106mm from the center of the objective lens.
based on geometry, to pass the full light cone and no more, the prism
hole should be (192-106)/192 x 50mm = 22.4mm diameter.
The actual prism hole is 21.5 mm.
The prism hole diameter is only 4% smaller than the full light cone.
The prism hole will vignette 7% of the incoming light.
Only the outer edge of the exit pupil all around is missing the full
illumination of the objective.
In this case, viewing the exit pupil down through the objective end
gives no true indication of the light loss due to vignette. There is
no obstruction caused by baffles. The vignette caused by the prism
field stop is responsible for clipping the diameter of the light cone
by only 4% and reducing the light in the image by 7%. the
observational method suggested shows an exit pupil obstructed 70%.
This should be proof that you cannot observe the exit pupil thru the
objective and use it to assess vignette. I suspect similar results
would be obtained with a variety of other binoculars.
edz
Anton Jopko
Ed,
what do your measurements say when the cone of light is not centered on the
optic axis by about the radius of your eyepiece field stop at the objective
focal plane?
thanks
anton
Ioannis
[snip]
OK, the above sounds reasonable to me. Kind of agrees with what I see on my
Apogee and Chinons.
Looking down from the front element, I see no baffles between the lens and
the prisms. So any vignetting that occurs, probably comes from the prism
face.
Happy observing!
Chris1011
>field in a pair of binoculars (no fair looking >now, you're probably
>expecting to see it)?
Hi Alan,
In normal daytime use, your eye's entrance pupil is never equal to the full
exit pupil of a binocular. Your eye effectively vignets the entire aperture of
the binocular, moreso than the internal baffles do. Therefore you do not see
the light dropoff in the daytime. At night your eye opens up to larger
diameter, but perhaps still not to the maximum theoretical exit pupil of the
bino, so you might not be aware for the slight loss of illumination. However, I
have seen the light dropoff of cheap large binos at night, especially those of
higher power and smaller theoretical exit pupils. Unfortunately I'm aware of it
and therefore tend to look for this.
Roland Christen
Chris1011
>method. In almost every binocular, I can >see 100% of the prism field
>stop. But in every one of these same >binoculars, usually 70% or 80%
>of the exit pupil is not seen. These >readings do not correlate at
>all.
The fact that the first baffle does not hide the first surface does not mean
that the light will reach the final destination, i.e. the eye of the observer.
In order for the light to go through each optical surface unhindered, it must
not encounter any spot where the optics are too small. They may get to the
first prism surface ok, but the next one could be too small again to accept
this light. If you cannot see the last exit, i.e. the exit pupil, then there is
another vignetting aperture somewhere deeper in the prism path, and you are not
getting the full illumination of your front objective.
Roland Christen
Alan French
news:20040401143728...@mb-m25.aol.com...
Roland,
Yes, given my "exit pupil as aperture" debate, I should have realized this.
Sometimes posts deserve more thought than they get, I fear.
I know what you mean when you say "unfortunately I'm aware of it and
therefore tend to look for this." A friend once commented he didn't like
eyepieces with a very large apparent field, say 80 degrees or so, because he
had to move his eye around to see the entire field. Now it bugs me a
little.
Clear skies, Alan
edz
this thread.
On my browser, there have been no posts update to any google thread
since 1:00 AM April 1st. I'm seeing info 32 hours behind real time.
I cannot yet see my last few posts.
edz
This morning I dismantled a second binocular, my Swift Ultralite 8x42.
Taking care to be even more accurate with my measurements than I did
with the orion 10x50, this is what I get for the 8x42.
Focal length objective = 159mm
Front prism face at 69mm from center of objective
Front prism face at 90mm from focal point
Prism hole required = 57% dia of objective
Prism hole required = 23.8mm
Actual prism hole = 21mm
Prism field stop is cutting off 12% of the diameter of the light cone.
Actual measured vignette due to prism housing opening being too small
is 12%.
When using the observational method of looking down inside the
objective from the edge, past the baffels, to the same side edge of
the prism housing, no baffles interfere with the prism housing.
Vignette due to baffles is 0%
When using the observational method of looking down inside the
objective from the edge, past the baffels, to observe the exit pupil,
80% of the exit pupil appears obstructed.
All the subsequent holes in the prism table can be smaller than the
first prism face, since the light cone is converging. My observations
indicate all prism shelf holes are equally sized.
The only piece of the equation I have not yet measured is the eyepiece
field stop. In all 15 cases of binoculars I own the eyepiece focal
length varies between 17mm and 21mm. Also in most cases the Afov is
60° to 65°. The ep field stop for 65° Afov is usually about 2-3mm
wider than the ep focal length. In all cases the ep barrel is even
wider. I'm just not confident I will find any vignette in the
eyepiece. If so, I don't think it would be a large order number.
Although this measure on the 8x42, done more accurately than the Orion
Ultraview, still shows vignette due to the prism housing, it is not
near what seems to be indicated by the viewing down the tube method.
Again, I think this actual measurement supports questioning the
validity of viewing down the tube at the exit pupil to assess the
degree if vignette.
edz
edz
edz
edz
In every binocular I've opened, 5 now out of 15, the prisms within are
of the same size. The second prism does not get smaller. And the
prism shelf openings that I have observed are all the same size. The
determinant of any vignette due to prisms will be found at the front
prism surface, at the prism field stop. Since the light cone
converges, anything that passes the first opening easily passes all
subsequent prism openings.
We have not discussed what I refer to in my articles as prism light
cutoff. This is caused by a too large prism housing sticking out into
the light path or by a prism edge showing through the prism field
stop. One condition blocks light, the other misses light. I have
previously measured both these conditions in many binoculars. They
can be easily observed looking down the tube and they can be seen as
straight edges in the exit pupil. The general range of light loss due
to these conditions is 3% to 5%. About half of all binoculars have
one of these conditions. These losses pale in comparison to what you
are leading us to believe may be present by observation of the exit
pupil through the objective.
I have clearly shown by actual measurements and analytical method the
two samples tested produced at most a 12% reduction in the diameter of
the light cone. In reality the total light loss, since it is not lost
from every point on the objective to every point on the prism, is not
the full 22% area of the obstructed ring, but is more on the order of
15%.
There remains only one other possible element in which any substantial
vignette can take place and that is the eyepieces. In the typical
focal length of the eyepieces used in all these various models, 17mm
to 21mm with Afov of 50° to 65°, there are few if any eyepieces
manufactured that would impart a substantial amount of vignette.
In order to substantiate the view down the objective of apparent
obstruction of the exit pupils to the extent of 70% and 80%, as is
observed in almost every condition, the remaining element, the
eyepieces, would need to vignette more than 50% of the remaining
light. I trust that no one will find any evidence that this is the
case.
Analytical methods clearly support that this observation of the exit
pupil from the edge of the objective does not give a true
representation of the vignette condition. You may yet find a reason
to explain why the exit pupil appears 80% obstructed when viewed down
through the objective, but it will not indicate the amount of
vignette.
edz
Alan French
>
> In every binocular I've opened, 5 now out of 15, the prisms within are
> of the same size. The second prism does not get smaller. And the
> prism shelf openings that I have observed are all the same size. The
> determinant of any vignette due to prisms will be found at the front
> prism surface, at the prism field stop. Since the light cone
> converges, anything that passes the first opening easily passes all
> subsequent prism openings.
Ed,
Things are not as necessarily as straight forward with the off-axis light
cone, because it is not passing straight through the system. Are you
looking at the off-axis bundles reaching the edge of the field stop in you
analysis?
The whole situation is similar to what happens in a Newtonian reflector. As
you move axis, the Newtonian secondary allows you to see the entire entrance
pupil for a while, but you reach a point where you can not see the entire
exit pupil, and the edge of the field is vignetted. How bad the vignetting
is depends on a number of factors, and there are plenty of programs
available to do the calculations.
With a refractor, including binoculars, the vignetting off-axis is
determined by the size and placement of the baffles, and the size and
placement of the optical components between the objective and the field
stop.
If you are taking a number of binoculars apart, look at the size and
placement of the eyepiece's field stop. With the eyepiece removed, put your
eye at the edge of the field stop. (You could place a cardboard or machined
"field stop" at the correct location for a more rigorous test. A small
aperture to look through would prevent your eye from also getting light from
some distance inside the field stop.) How much of the objective can you
see?
Clear skies, Alan
Chris1011
>pupil from the edge of the objective does >not give a true
>representation of the vignette condition. >You may yet find a reason
>to explain why the exit pupil appears 80% >obstructed when viewed down
>through the objective, but it will not >indicate the amount of
>vignette.
If you don't see the exit pupil from the front, then light does not reach the
eye. It's as simple as that. I'm not familiar with the type of binos that you
have, but it may be that either you are misinterpreting what you are seeing, or
there may be other stops along the prism path. There is also the possibility
that the prisms are not high index glass and do not reflect light at the 45
degree angle beyond a certain incoming angle.
A picture is worth a 1000 words, so if possible, take some images of the exit
pupil through the front aperture using a very small F-stop on the camera (F16
for example) to simulate a thin light pencil, then study the shape of the exit
pupil.
Maybe that's too much work and it's better just to enjoy your optics.
Have fun,
Roland Christen
edz
> pupil from the edge of the objective does not give a true
> representation of the vignette condition.
Today I measured my 16x70 Fujinons.
Keep in mind, using the visual assessment of observing the exit pupil
from the edge of the objective resulted in seeing an exit pupil about
70% obscured. By the definition proposed, that is supposed to
indicate not only that vignette is present, but that it is fairly
substantial.
Here is what I found. This was far more difficult because I did not
open the binocular. However, my measurements could be checked.
I found the focal length is 300mm
The distance from the center of the objective to the first prism is
172mm
The distance (effective) from the prism face to the focal point is
128mm
The prism opening measures 30mm
The prism face is placed 43% the distance along the light cone. In
order to pass all the light, the prism opening needs to be a minimum
of 43% x 70mm = 30.1mm
Based on the measurements obtained, the opening vignettes less than 1%
the diameter of the objective.
The analytical method shows no vignette present or just very slightly
a minor amount. The observational method shows the exit pupil
obscured by 70%.
Which do you think is correct? Even if my measurements on this one
are +/- 5%, clearly the Fujinon 16x70, one of the premier astronomy
binoculars on the market today, has very little if any vignette
present.
The observational method would seem to indicate otherwise, and I
believe it would be a misrepresentation of the actual condition.
edz
Chris1011
believe it would be a misrepresentation of the actual condition.>>
Based on your observations and analysis, it is clear that you do not understand
vignetting.
I will not argue further with you.
Roland Christen
Alan French
> Based on the measurements obtained, the opening vignettes less than 1%
> the diameter of the objective.
>
> The analytical method shows no vignette present or just very slightly
> a minor amount. The observational method shows the exit pupil
> obscured by 70%.
Ed,
It sounds like you are looking at two different situations here. Your
analysis is for on-axis light. Your observation is for off-axis light at
the very edge of the field. These situations are quite different.
I get the impression you are too busy trying to argue against something your
gut feels is incorrect to really give it much thought.
Clear skies, Alan
edz
I understand you have far more knowledge of optics than I do. I'm
trying to see this. Work with me just a little more if you will.
Right up front I'll state, I have seen the vignette that you described
present in the system. The D shape you spoke about is clearly present
in the system when the light is not directly on axis. I needed to
clearly see it. I decided to go for the exit pupil, since I know the
exit pupil doesn't lie. A key for me was to find a way to determine
at what point on the objective lens the D shaped was not longer
present. I believe the method I used to see it allows me to now
measure it. I can't tell how much is attributable to each component
in the system, but I can see the amount of vignette in the total
system.
I tested the baffles and I tested the prism opening. I found none due
to baffles and I described the vignette I measured due to prism
opening. In the samples I tested, generally, the prism opening
contributed from just a fraction of percent to 12%. That represents
just my samples and not a range for all binoculars. But neither of
these tested the eyepiece or the light exiting the prisms. But
obviously, if so much was to be found I needed to find a way to look
here for it. I wanted to devise some method I could test this in
place. I decided to look at the exit pupils. Here's what I did.
I mounted my 16x70 Fujinons with the eyepiece end pointed at a white
wall about 20mm away from the eyepiece end. Using a Helix Laser
circle and crosshair target hologram collimator, I observed the
slightly enlarged image of the exit pupil on the wall while I moved
the laser to various points along the objective diameter. The intense
laser crosshairs image was easily observed both in the image on the
wall and on the surface of the objective lens. The red light provided
a sharply lit exit pupil.
I started out with the eyepieces as close to the wall as possible in
an attempt to observe the exit pupils in true size. This proved
impractical. The image was too small to take useful measurements and
the binoculars were so close to the wall it made observation and
measurement difficult. By moving the binoculars slightly away from
the wall, I enlarged the exit pupil image to 20mm, it did not change
in shape at all, and I had enough room to measure the image. The
image was now large enough so measurements were not necessary to
tenths of mm.
Much to my surprise, (but I am sure not to the surprise of Roland) and
confirming what Roland is saying, the laser did not produce a fully
round exit pupil image on the wall until the laser was move in 18mm
from the edge of the 70mm objective lens. As the laser was moved from
the very edge of the objective lens, the D shape could easily be
observed to grow in size. At 18mm in from the edge of the objective,
the exit pupil was completely round and the full 20mm image size of
the exit pupil projected on the wall. With the laser at the extreme
edge of the objective, the cat's eye shaped exit pupil image measured
only 8mm across its narrow side.
18mm of the outer edge of the Fujinon 70mm objective is providing
something less than 100% light in the resultant exit pupil. 18mm is
almost exactly 25% the full diameter of the objective. Therefore,
only the central 50% of the objective is providing 100% of its light
to the exit pupil. The extreme outer edge of the objective produces
an exit pupil only 40% as wide as full. I believe this is indicating
the edge of the objective is providing light to 40% of the exit pupil.
By proportion, it can easily be determined for every point on the
objective between the edge and 18mm inside what % light is being
delivered to the resultant exit pupil image.
Nearly the same results were obtained with the Swift Ultralite 8x42.
The entire round exit pupil was first observed when the laser target
was projecting from a point approx. 10mm in from the very edge of the
objective. At the extreme outer edge of the objective, the light
projected to the exit pupil produced an image only 2-3mm wide, approx
10-15% of the full size exit pupil.
I'm not from Missouri, but "show me" seems to come to mind. I have
now seen for myself the effect you previously described. "I can't
imagine" seems to be a phrase that has no place in the determination
of optical performance. I suppose a good dose of wait three days
before I speak would do me some good.
I would ask, do you think I now understand vignette, and do you think
this method represents a feasible way to measure it? Also, having
seen it in the exit pupil, I wouldn't be surprised if I cut a 70mm
scale and laid it over the objective, I would probably see that the
full exit circle does not appear in my view until I've moved my eye
18mm in from the edge, similar to what I measured with the crosshair
laser target.
thanks,
edz
John Pane
>Keep in mind, using the visual assessment of observing the exit pupil
>from the edge of the objective resulted in seeing an exit pupil about
>70% obscured. By the definition proposed, that is supposed to
>indicate not only that vignette is present, but that it is fairly
>substantial.
The amount of obstruction measured this way does not translate
directly into the severity of vignetting (i.e. 70%). While this test
shows that a certain part of the objective doesn't contribute light to
the obscured portion of the exit pupil, for any particular part of the
exit pupil, it may be only a small fraction of the objective that
fails to contribute light. Hypothetically, if about 90% of the
objective does contribute to that part of the exit pupil, the
vignetting will be closer to 10%, not 70%.
John
--
Alan French
> The prism face is placed 43% the distance along the light cone. In
> order to pass all the light, the prism opening needs to be a minimum
> of 43% x 70mm = 30.1mm
>
> Based on the measurements obtained, the opening vignettes less than 1%
> the diameter of the objective.
Ed,
Actually, your numbers show clearly that vignetting will start not far
off-axis. The first prism face barely accepts all the on-axis light.
Clear skies, Alan
Chris1011
vignetting in Binoculars.
I have many pairs myself, gathered over a lifetime. One of the worst, actually
the worst is a pair of 9x63 roof prism binos that were popular about 20 years
ago (variously called Little Giants or some such name back then). They show a
round exit pupil when examined from the eyepiece end, making it look like they
used Bak4 prisms. However, they used every trick in the book to trick people
into thinking they were high quality.
The prisms are BK7 and would have shown the characteristic blue square shape in
the eyepiece end, except that there is a very small field stop near the
eyepiece end that removes this telltale feature. As a result, the center of the
field is illuminated by less than 45 mm and the edges of the field by about
30mm of the objective diameter. The front objective is single layer coated, and
the prisms and most of the eyepiece elements are not coated at all.
My best pair is one I found after looking through dozens of contenders. It is a
Minolta 10X44 roof prism bino which shows a fully round exit pupil from the
front objective across the entire diameter. The coatings are first class
throughout. It is measurably brighter than the 9x63 on deep sky objects and
makes for a great daytime bino because of its light weight. Its main defect is
some lateral color and astigmatism at the field edges. Alan French's Svarovski
binos are similar in size, and it seems to have a better eyepiece set because
they are sharper than my Minoltas at the extreme field edges.
Roland Christen
edz
i should have said the prism is placed 43% along the light cone as
measured from the focal point. As far as I could determine, the prism
opening was just large enough(99%) to accept the entire light cone.
However, the point was well made that this only measures one source of
vignette and I think my light tests of exit pupil do far more to show
the true extent of vignette than this simple measurment. While
useful, it is not the whole story.
edz
"Alan French" <adfrenchre...@nycap.rr.com> wrote in message news:<Ul%bc.26486$nr4....@twister.nyroc.rr.com>...
anton jopko
I think we have to keep in mind that looking through the objective and
through the eyepiece are not inverses of each other.
observing through the eyepiece, the light must come into the objective in a
parrallel bundle with a very small angle relative to the optical axis.
looking through the objective however, light may come through the eyepiece
from many different and large angles some of which do not occur in the
previous situation.
I feel that the D shaped exit pupil viewed from one edge of the objective is
really irrelevant as far as percent obstruction of the exit pupil goes since
the light from the other edge of the objective still passes through the
supposedly invisible portion of the exit pupil.
my 2 cents,
anton
Chris1011
>really irrelevant as far as percent >obstruction of the exit pupil goes since
>the light from the other edge of the >objective still passes through the
>supposedly invisible portion of the exit >pupil.
>my 2 cents,
>anton
Think about what you just said, Anton. You have a "feeling" that something is
so. Feelings are nice to have, but don't always properly describe physical
reality. People used to "feel" that the world was flat. They could not imagine
standing on a sphere.
In any case, your type of argument allows manufacturers to exploit the amateur
community. There is a saying among the less scrupulous: "they will never know
the difference".
Good luck out there,
RC
edz
> Ed and others,
> I think we have to keep in mind that looking through the objective and
> through the eyepiece are not inverses of each other.
> I feel that the D shaped exit pupil viewed from one edge of the objective is
> really irrelevant as far as percent obstruction of the exit pupil goes since
> the light from the other edge of the objective still passes through the
> supposedly invisible portion of the exit pupil.
> anton
Anton,
I think a review of all the previous posts will show that no one
voiced skepticism as much as I of the view through the objective. To
prove it for myself, I employed the use of a laser light, the closest
thing I could get to a point source for testing the binocular. I
viewed the image of resultant exit pupil projected onto a white wall.
By doing so, I was able to observe the D shape ( I would refer to it
more of a cat's eye shape, but D is close enough) IN THE EXIT PUPIL.
The laser allowed moving the light source across the face of the
objective to observe the changing exit pupil. The image on the wall
is a real image. The projection is a true picture of the shape of the
exit pupil. Enlarged to 20-30mm, it was simple to observe. Having
seen it and clearly understanding what it was showing me, I could then
observe that the appearance of the exit pupil by looking down thru the
objective showed nearly if not exactly the same thing.
edz