Varible ND Filter?
Daniel
body setup.
Basically, when shooting jets I stick it in AV or manual and there's no
problem. However, the problem comes when switching to shutter priority and
a much slower shutter speed to shoot helicopters/prop aircraft (to get
motion blur on the rotors/props). If there's decent light it means that the
lens then has to stop itself way down for correct exposure even at ISO 100
and therefore you're faced with diffraction limitation and also even the
smallest amount of sensor dust is visible against the sky.
Obviously, I could stick a ND filter on the lens when shooting helicopters,
but it's not ideal to keep screwing it on and off throughout the weekend. I
was thinking of maybe a quick release ND filter that just clips on and off
the front of the lens (sort of like the expodisc does), but couldn't find
one. I did come across a variable ND filter that ranges from 2-8 stops,
which looks like a good idea (http://www.singh-ray.com/varind.html), but
it's a bit on the pricy side and also because it would be on the lens all
the time it will effect AF performance when tracking jets due to the 2 stop
loss of light, especially if I'm also using a TC at the time. Any other
suggestions?
Toby
since you have sharp edges and high contrast in your subjects.
Toby
"Daniel" <m...@privacy.net> schrieb im Newsbeitrag
news:c5Wdnf07sqk7kjvU...@pipex.net...
Nicko
If this is not a troll, it should be.
Chris Malcolm
> Looking for advise on shooting helicopters at air shows using a one lens/one
> body setup.
> Basically, when shooting jets I stick it in AV or manual and there's no
> problem. However, the problem comes when switching to shutter priority and
> a much slower shutter speed to shoot helicopters/prop aircraft (to get
> motion blur on the rotors/props). If there's decent light it means that the
> lens then has to stop itself way down for correct exposure even at ISO 100
> and therefore you're faced with diffraction limitation and also even the
> smallest amount of sensor dust is visible against the sky.
If you're using only one lens dust shouldn't be a problem -- just
clean the sensor if necessary before fitting the lens.
Is this just speculation or have you actually tried this? Given
typical numbers for a sunny day exposure and blurring rotor blades I
don't see you getting into problematically diffracted territory. But
you haven't specified the sensor size or target print/display size,
how much rotor blur you want (complete circle?), and the shutter speed
you're using to achieve it.
--
Chris Malcolm
Daniel
news:49a610b2$0$243$bb4e...@newscene.com...
>> Looking for advise on shooting helicopters at air shows using a one
>> lens/one body setup.
>>
>> Basically, when shooting jets I stick it in AV or manual and there's no
>> problem. However, the problem comes when switching to shutter priority
>> and a much slower shutter speed to shoot helicopters/prop aircraft (to
>> get motion blur on the rotors/props). If there's decent light it means
>> that the lens then has to stop itself way down for correct exposure even
>> at ISO 100 and therefore you're faced with diffraction limitation and
>> also even the smallest amount of sensor dust is visible against the sky.
>>
>> Obviously, I could stick a ND filter on the lens when shooting
>> helicopters, but it's not ideal to keep screwing it on and off throughout
>> the weekend. I was thinking of maybe a quick release ND filter that just
>> clips on and off the front of the lens (sort of like the expodisc does),
>> but couldn't find one. I did come across a variable ND filter that
>> ranges from 2-8 stops, which looks like a good idea
>> (http://www.singh-ray.com/varind.html), but it's a bit on the pricy side
>> and also because it would be on the lens all the time it will effect AF
>> performance when tracking jets due to the 2 stop loss of light,
>> especially if I'm also using a TC at the time. Any other suggestions?
> Even with an 8x ND your autofocus should have plenty of light, especially
> since you have sharp edges and high contrast in your subjects.
True.
Daniel
news:70n8nnF...@mid.individual.net...
Tried it plenty of times. On a normal summer day it meters about 1/60, f/22
@ ISO 100.
1/60 may sound a bit slow, but it gives the perfect amount of rotor blur and
with a slow helicopter and IS, it's not a problem. Diffraction limiting
starts to cut in at about if/11 on my 8MP 1.6 cropped sensor.
Daniel
news:qpWdnQPNQtwl5DvU...@pipex.net...
> True.
Actually, it's got me thinking. Why do Canon disable AF over f/5.6 min
aperture?
Say you have an f/4 lens and stick a X2 converter on it, why disable AF when
you could be shooting a well illuminated subject with lots of contrast? Are
they just trying to make it fool proof so that someone doesn't try to shoot
with a min aperture of f/8 in a poorly lit condition?
Matt Ion
> Obviously, I could stick a ND filter on the lens when shooting
> helicopters, but it's not ideal to keep screwing it on and off
> throughout the weekend. I was thinking of maybe a quick release ND
> filter that just clips on and off the front of the lens (sort of like
> the expodisc does), but couldn't find one.
Take a look at Cokin's Creative System line:
http://www.cokin.com/ico1-p1.html
> I did come across a variable
> ND filter that ranges from 2-8 stops, which looks like a good idea
> (http://www.singh-ray.com/varind.html), but it's a bit on the pricy side
Looks like a pair of stacked CPLs... which was going to be my other
suggestion. The downside of that is that you lose 3-4 stops right off
the top, even at its "brightest" adjustment. Of course, a pair of CPLs
may also be a little cheaper...
Jørn Dahl-Stamnes
> Actually, it's got me thinking. Why do Canon disable AF over f/5.6 min
> aperture?
That has nothing to do with using ND filter. I have used a ND 3.0 and the AF
still work.
--
Jørn Dahl-Stamnes
http://www.dahl-stamnes.net/dahls/
ASAAR
> Yeah, I've already read about this technique with polarizer's, however it's
> still not convenient to keep switching screw-ons.
>
> At the moment I'm considering just using some ND gel and masking tape. Bit
> crude, but hey.
I agree with Gordo's comment. Read what Thom Hogan has to say
about the Cokin P Holders. Note that he feels that screw-in
graduated ND filters aren't very useful and that graduated ND
filters work more easily with wide angle than with telephoto lenses.
Michael Benveniste
> I agree with Gordo's comment. Read what Thom Hogan has to say
> about the Cokin P Holders. Note that he feels that screw-in
> graduated ND filters aren't very useful and that graduated ND
> filters work more easily with wide angle than with telephoto lenses.
I agree 100% about graduated ND's, but I think the original
poster wishes to "darken" the entire field of view, not
just part of it.
--
Michael Benveniste -- m...@murkyether.com (Clarification required)
Legalize Updoc.
ASAAR
>> I agree with Gordo's comment. Read what Thom Hogan has to say
>> about the Cokin P Holders. Note that he feels that screw-in
>> graduated ND filters aren't very useful and that graduated ND
>> filters work more easily with wide angle than with telephoto lenses.
>
> I agree 100% about graduated ND's, but I think the original
> poster wishes to "darken" the entire field of view, not
> just part of it.
Yes, within seconds of hitting the Send button I realized that the
OP hadn't mentioned *graduated* ND filters, but was more concerned
about needing to repeatedly screw the standard ND filters on and
off. I figured that someone would be observant enough to catch my
mistake, and the main idea was to second the idea of using Cokin's
holder. I had read Thom's filter article just a few hours before
and I guess that the "graduated filters" part of it registered more
strongly than the rest of it. One interesting minor point I took
away from Thom's article is that he probably spends more for filters
than many of us here in the ng's spend for cameras, and he buys what
he needs and uses, another thing that sets him apart from some of
us; *some* I'll say this time, not *many*. :)
Toby
I think that is exactly the reason; also perhaps because the AF would be
very slow or possibly not work correctly in marginal conditions, leading to
lots of complaints.
sligoNo...@hotmail.com
How about choosing shutter priority and changing it as needed?
C J Campbell
> Daniel wrote:
>
>> Obviously, I could stick a ND filter on the lens when shooting
>> helicopters, but it's not ideal to keep screwing it on and off
>> throughout the weekend. I was thinking of maybe a quick release ND
>> filter that just clips on and off the front of the lens (sort of like
>> the expodisc does), but couldn't find one.
>
> Take a look at Cokin's Creative System line: http://www.cokin.com/ico1-p1.html
Yeah, I would use Cokin filters here, too.
--
Waddling Eagle
World Famous Flight Instructor
Alan Browne
>
> Actually, it's got me thinking. Why do Canon disable AF over f/5.6 min
> aperture?
>
> Say you have an f/4 lens and stick a X2 converter on it, why disable AF
> when you could be shooting a well illuminated subject with lots of
> contrast? Are they just trying to make it fool proof so that someone
> doesn't try to shoot with a min aperture of f/8 in a poorly lit condition?
I don't believe it is the loss of light so much as the geometry of how
the rays of light arrive on the AF sensor when the aperture is smaller.
(I don't know this for a fact).
It just seems that having a disable function based on aperture is
non-sensical as it does not account for what amount of light is actually
there. So, it may be a geometry issue.
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Kennedy McEwen
<m...@privacy.net> writes
>Why do Canon disable AF over f/5.6 min aperture?
>
lens starts to vignette the areas it is specifically looking at.
>Say you have an f/4 lens and stick a X2 converter on it, why disable AF
>when you could be shooting a well illuminated subject with lots of
>contrast? Are they just trying to make it fool proof so that someone
>doesn't try to shoot with a min aperture of f/8 in a poorly lit
>condition?
>
It isn't just the amount of light, it is the design of the AF sensor
system. Phase Difference (PD) AF compares the images created by light
passing through opposite sides of the lens and measures the image
separation. It is a bit like a split image range-finder with the
baseline being the width of the front aperture if the lens at the
nominal AF aperture.
You can see this on http://www.kennedym.demon.co.uk/Canon/Canon%20AF.jpg
The shaded areas on either side of the main lens are the sub-apertures
than the AF system operates with. In the f/5.6 AF sensors these
sub-apertures extend from f/5.6 at their outer edge to around f/9.5 at
their inner edge. In other words, the AF sensor extends from its
nominal f/# to about 1.5 stops higher - outside of these limits it is
blind.
If your lens combo is nominally f/8 then very little light gets through
to the AF sensor at all, focus becomes very erratic even in high
contrast conditions and it certainly doesn't perform to spec.
Incidentally, this diagram also demonstrates how putting a faster lens
on the camera doesn't let any more light into the AF sensor, so it
doesn't improve the low light capabilities of the AF sensor. Once you
have a lens that is fast enough to enable the f/2.8 AF sensor, that is
the limit - a faster lens just doesn't help at all.
You can defeat the Canon AF maximum aperture lockout using the contact
tape trick on the extender, which stops the camera from reading what the
maximum aperture of the combo is. The contacts to tape over are shown
here http://www.fredmiranda.com/TipsPage/example.html
With the 100-400 f/4.5 to f/5.6 lens and a 2x convertor giving a 2 stop
increase in the combo, this trick allows AF to operate, albeit only in
bright light and quite erratically, at 100mm where the nominal maximum
aperture of the combo is f/9. However, by 125mm, when the nominal
maximum aperture of the combo is almost f/9.5, the AF simply hunts even
in bright light and is essentially non-functional.
Doug Kerr has written up a very good derivation of AF from it's
predecessor, the split image viewfinder, and how they work at
http://doug.kerr.home.att.net/pumpkin/Split_Prism.pdf Recommended
reading for anyone interested in PD AF.
--
Kennedy
Yes, Socrates himself is particularly missed;
A lovely little thinker, but a bugger when he's pissed.
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