1. Result of Eyepiece Transmission testing

[Markus Ludes]

Hi Everybody, as promissed first run of eyepieces have been transmission
tested. The testresults says nothing about the optical quality, eyerelief,
fieldcorrection or other stuff. It tells us only the total lighttransmission at
diffrent wavelenghtes.

I have for each tested eyepiece a print graphic and a excel tabele with
numbers, we will create on my webside a section where we show them, this are
very many datas and wil take some time.

However a few interested numbers I like to publish here to start a interested
discussion.

Please consider that lighttransmission results depends on glas quality, coating
quality, numbers of elements and numbers of cementings

Lets start with 4 lens eyepieces, like Orthos and Plössls, both using 4 air-to
glas surfaces, so they can be compared. I show now only the visual range and
toppoint of transmission . The testrun was made from 300 nm to 800 nm
Numbers shown are %

Item 450 nm 500 nm 550 nm 600 nm 650 nm top transmission

3-element eyepieces

Zeiss 25mm 54° 96.48 98.17 98.36 98.22 97.48 98.41 % at 542 nm

4-element eyepieces

Zeiss A-6 mm 93.46 95.77 96.20 96.15 95.17 96.4 % at 544 nm
Pentax O-6 mm 95.61 96.52 97.34 97.86 97.87 98.23 % at 616 nm
Clave 6 mm 94.44 97.26 97.52 97.77 98.09 98.31 % at 622 nm
Synta PL 6.3 92.93 94.96 95.52 96.07 96.30 96.37 % at 642 nm

Pentax O-7 mm 92.84 94.94 96.67 97.39 96.91 97.52 % at 606 nm
Kasai Ortho 7 94.38 95.46 95.47 95.46 94.89 95.56 % at 604 nm

Zeiss A-10 mm 94.51 95.96 96.77 97.25 96.67 97.79% at 550 nm
Kasai Or 9 94.37 96.17 96.17 96.72 96.68 96.90 % at 574 nm
NIKON 12.5 87.79 93.35 95.34 95.37 94.61 95.72 % at 574 nm
Synta PL 10 88.42 91.87 93.44 94.48 94.58 94.73 % at 618 nm

Zeiss A-16 mm 92.39 96.00 97.34 97.11 96.32 97.34 % at 550 nm
Pentax O-18 mm 93.30 94.92 96.70 97.95 98.34 98.42 % at 628 nm

Tele Vue PL 20 96.48 97.38 98.02 98.81 95.94 98.88 % at 598 nm
Synta PL 20 88.43 92.70 94.37 95.36 96.19 96.37 % at 682 nm

Zeiss A-25 mm 94.80 97.28 97.97 98.22 97.72 98.36 % at 576 nm
Kasai Or 25 92.37 95.59 96.21 96.48 96.14 96.67 % at 576 nm
NIKON 25 mm 92.20 95.20 96.26 95.65 95.35 96.40 % at 570 nm

Zeiss A-34 mm 95.27 97.97 97.97 98.32 97.96 98.50 % at 544 nm
Kasai Or 25 92.37 95.59 96.21 96.48 96.14 96.67 % at 576 nm

5-element eyepieces

Takah. LE 5 89.03 92.88 93.15 93.85 93.30 94.06 % at 620 nm
Takah. LE 7.5 90.15 92.30 92.69 94.32 94.05 94.54 % at 610 nm
Takah. LE 12.5 92.14 94.01 95.19 96.40 94.72 96.60 % at 610 nm
Olympus 12.5 86.71 92.93 95.45 95.36 94.25 95.88 % at 576 nm
INTES MICRO 12 85.84 91.25 91.47 89.59 87.45 91.90 % at 574 nm
Zeiss 16mm 62° 89.70 93.19 93.93 92.83 91.39 93.96 % at 542 nm
INTES MICRO 21 85.24 90.49 93.14 93.50 92.84 93.71 % at 574 nm
Takah. lE 24 94.17 96.12 96.51 96.23 94.52 96.67 % at 564 nm

Zoom Eyepieces
Tele Vue 3-6 90.70 94.53 96.05 96.11 96.10 96.50 % at 612 nm
Leica 7-22 91.87 93.94 93.84 93.71 91.78 94.04 % at 592 nm
Zeiss 8-25 87.51 91.33 94.21 95.15 92.62 95.23 % at 592 nm
NION 7-21 91.87 94.50 94.58 96.35 96.96 96.99 % at 638 nm

Widefields

NIKON 17-72° 92.31 92.52 93.42 95.54 96.19 96.41 % at 640 nm
Zeiss 16.7-69° 87.90 92.86 95.93 96.70 94.41 96.97 % at 588 nm
Tele Vue Pan 15 83.93 89.73 90.47 91.55 92.21 92.58 % 618 nm
TV Radian 18 90.39 94.10 94.91 96.78 96.34 97.36 % at 622 nm

TV Radian 14 87.58 92.63 93.75 94.87 92.65 95.71 % at 578 nm
NIKON 13-72° 89.48 92.41 93.68 95.19 94.57 95.47 % at 622 nm
Zeiss 12.5-69° 87.97 93.48 95.75 96.72 95.59 97.79 % at 602 nm

TV Radian 10 86.52 92.23 93.53 95.30 95.09 95.65 % at 634 nm
TV Radian 6 84.21 87.22 89.47 92.20 90.63 92.44 % at 606 nm
TV Radian 4 84.77 88.98 91.33 92.95 91.31 93.34 % at 616 nm
TV Radian 3 84.99 88.01 91.06 92.17 89.33 92.32 % at 592 nm

TV Nagl. 16-T5 93.48 93.53 94.32 96.48 95.71 96.71 % at 618 nm
Meade 6.7 UWA 78.50 85.86 89.86 91.25 90.57 91.25 % at 600 nm
TV Nagler 4.8 87.76 91.37 91.52 94.58 95.83 95.90 % at 640 nm

For new Naglers I have graphics but not yet the numbers

so here the rough numbers for new Naglers
TV N 5mm T6 91 92 96 97 94
TV N 7mm T6 91 92 95 97 95
TV N 9mm T6 91 92 94 97 97

Interested is that some eyepieces have higher transmission on 600 nm than at
the best wavelenght between 500 and 550 nm. Here some manufactors should talk
with coating company to shift the coating a bid. Very impressive for me to see
that the new Zooms have about the same transmission than modern high end
Plössl, Widefields and even orthos. I think the time where we said Zooms are
dimmer is over. Also impressive is that the Kasai Orthos, ( sold in USA by
Orion) holding up in transmission with super famous eyepieces and that cheap
chinese Super Plössl also holding very well. Also interesting that some longer
focuse eyepieces with thicker glas have better transmission than same series
short focuse eyepieces with less glasthickness. Intersting is also that the
widefieldspoting scopes eyepieces from NIKON and Zeiss beating other
astronomical widefields in transmission even with more lenses partly.

Now the tester have 2 weeks holiday, after that we testing the Pentax XL and
some ultrawidefields, like Widescan 30 mm, Zeiss 30 mm, Leica 30 mm and Nagler
31 mm

Now have fun with your discussions

Markus

BTW the testing was not to expensive

--
Posted from pec-98-152.tnt8.f.uunet.de [149.225.98.152]
via Mailgate.ORG Server - http://www.Mailgate.ORG

[Mike Linnolt]

Markus,

Thanks for conducting these very useful tests! It helps fill in a void of
information on this important subject. Regarding the apparently
contradictory results of thicker/ more elements actually having better
transmission - I believe it is due to the type and quality of
anti-reflection coatings applied.

I think the next step would be to test some of the inexpensive eyepieces,
such as the Siebert 7mm, 10mm, 21mm, 32mm. And the University optics orthos
4mm, 5mm, etc. There are a lot of good comments on these particular ones
comparing to high end models, so testing them quantitatively should put to
rest any lingering questions.

Great work!
Mike Linnolt
Hawaiian Astronomical Society
http://www.hawastsoc.org

[Phil]

Will you be posting these results on a web site ?

"Markus Ludes" <apm_tel...@web.de> wrote in message
news:b7898ae2b7e0d05cf67...@mygate.mailgate.org...

[Del Johnson]

I previously claimed that the 8mm Radian was brighter than the 6mm Radian,
even after accounting for the change in magnification. Your results for the
Radians (10mm is the same design as the 8mm) support my subjective
observation.

Del Johnson

"Markus Ludes" <apm_tel...@web.de> wrote in message
news:b7898ae2b7e0d05cf67...@mygate.mailgate.org...

> Hi Everybody, as promissed first run of eyepieces have been transmission
> tested. The testresults says nothing about the optical quality, eyerelief,
> fieldcorrection or other stuff. It tells us only the total
lighttransmission at
> diffrent wavelenghtes.
>

> TV Radian 18 90.39 94.10 94.91 96.78 96.34 97.36 % at 622
nm
> TV Radian 14 87.58 92.63 93.75 94.87 92.65 95.71 % at 578
nm

> TV Radian 10 86.52 92.23 93.53 95.30 95.09 95.65 % at 634
nm
> TV Radian 6 84.21 87.22 89.47 92.20 90.63 92.44 % at 606
nm
> TV Radian 4 84.77 88.98 91.33 92.95 91.31 93.34 % at 616
nm
> TV Radian 3 84.99 88.01 91.06 92.17 89.33 92.32 % at 592
nm
>
>

> Markus
>
>

[Sue and Alan]

Del,

I do not think you could visually detect a difference of 3 or 4
percent in light transmission, even assuming these numbers apply to
the eyepieces you compared.

There are problems comparing eyepieces giving different
magnifications. With stars, increasing magnification results in a
darker sky background until you reach the point where the Airy disc
becomes visible. This could certainly account for stars looking
brighter in a 6mm eyepiece than in an 8mm eyepiece.

With deep sky objects, having a larger image on the retina tends to
make dim objects easier to perceive, and as a result they look
brighter.

At any rate, I do not think you can say for certain that the
difference you saw was due to a difference in like transmission.

Clear skies, Alan

"Del Johnson" <dela...@san.rr.com> wrote in message news:<IlwG7.22804$D5.88...@typhoon.san.rr.com>...

[JMc]

I agree and recall from somewhere that our eyes are poor at perceiving
differences in light intensity less than +/- 10%. At the center of the
FOV, perhaps the biggest differences in eyepieces have more to do with
the quality of polish, scattering within the glass, and internal
reflections.

Throughput just measures the average light transmitted - it doesn't
really gauge the loss of contrast from scattering and reflections. I'd
rather use an eyepiece with high contrast no internal reflections versus
an eyepiece with poor polish and 99% transmission .

Jim McSheehy

[Ron B[ee]]

Now, I haven't thought of this: contrast. An excellent point Jim.
By playing with our computer monitor (or imaging program),
one can see the brightness vs contrast. But, through the eyepiece,
what sort of instrument can measure contrast?

So the $$$ eyepiece question then is: which is better, brighter
image (<= 10%) and less contrast or less brightness and more
contrast?

Ron B[ee]
-----------

"JMc" <tri...@onebox.com> wrote in message
news:3BEE8380...@onebox.com...

[Louis Boyd]

"Ron B[ee]" wrote:
>
> Now, I haven't thought of this: contrast. An excellent point Jim.
> By playing with our computer monitor (or imaging program),
> one can see the brightness vs contrast. But, through the eyepiece,
> what sort of instrument can measure contrast?
>
> So the $$$ eyepiece question then is: which is better, brighter
> image (<= 10%) and less contrast or less brightness and more
> contrast?

If an eyepiece has a 10% transmission loss that light has to go
somewhere. If there were only one reflecting optical surface that might
just be back out through the telescope. Fat chance.
It matters too in what part of the field the contrast is poor. A
reflection can be spread over the entire field or just cause a little
annoying spot somewhere in the field. For planetary viewing the failure
to fully correct any of the many possible aberations can cause poor
contrast limited to a very short angular distance around the light
source. That can be much worse than a flare or full field reflection
for trying to see faint detail on a bright planet surface.

How to measure it? Probably the best way is with a CCD camera with an
appropriate lens to simulate the eye, but with several times better
resolution and better color correction than the eye has. Such a camera
will have to be tested to determing how much of the loss of contrast it
is contributing. You've taken on a complex task. You'll need to be
able to scan a focused point source, preferably of white light, across
the field of the eyepiece and beyond in case there are reflections from
locations outside of the field. Unfortunately most ccd cameras have
their own set of problems with internal reflections. Sorting out those
caused by the camera from those caused by the eyepece will be fun.

Another thing which affects eyeiece performace is the f ratio of the
light cone from the objective. An eyepiece which works well with an
f/10 objective may not do well with a f/4 objective. Microscope
eyepieces almost never work well with large fast lenses or mirrors. The
wider angle of light entry into the eyepiece can affect the contrast.
Also there's field flatness, pincushion distortion, and a number of
other things which affect eyepiece performance with a given objective.
An eyepiece is not a "stand alone" instrument. You can only really tell
it's quality on the instrument it will be used with. If you're trying to
advise people on eyepiece quality there are a lot more potential
problems than just brightness and contrast.

--
Lou Boyd
Fairborn Observatory

[Brian Wirthlin]

Measuring the modulation transfer function would address contrast, but
it won't fix the lack of a statistically valid sample.

Louis Boyd <bo...@apt0.sao.arizona.edu> wrote in message news:<3BEF48FD...@apt0.sao.arizona.edu>...