Strange flare with 5dII. Please check.

Started Feb 12, 2009 | Discussions
robjm New Member • Posts: 6
Re: No -- that's not why you cover the eyepiece

Right. And now that I look at other shots from the series, I realize that indeed there are additional light sources just out of frame in this shot. Looking forward to a Canon response if it is indeed a simple reflection issue that can be reduced - at least.

Nicolaj Roos Regular Member • Posts: 236
Re: Strange flare with 5dII. Please check.

Cheap filters will do that.

Victor Engel Forum Pro • Posts: 18,567
Read the thread

That's not what's going on here.
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Its RKM Veteran Member • Posts: 3,135
Oh for pity sake!

Victor Engel wrote:

During exposure, light entering through the eyepiece is blocked from
entering the main chamber of the camera.

This has, and can have, NOTHING to do with light coming in through the viewfinder! Does anyone really think that light coming through the viewfinder will change just by turning the camera upside down?

It is, and always has been, a problem with light being reflected from the back of the mirror. For many reasons, it is not possible to reduce reflections from the back of the mirror as well as from the base of the mirror chamber. I beleive that this is because of the thickness of the mirror and the fact that it must flip up 45deg before the shutter opens, moving the back slightly further from the focal plane and exposing the edge which cannot be blackened effectively. There is a narrow range off the bottom of the frame area, where highlights can hit this edge and create the reflections noted in all of these examples. No such edge exists on the bottom of the mirror box and so no problem exists there.

This has nothing to do with light through the viewfinder!

Sorry Victor, your response didn't seem clear enough!
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Its RKM

Its RKM Veteran Member • Posts: 3,135
Re: Strange flare with 5dII. Please check.

Nicolaj Roos wrote:

Cheap filters will do that.

Yes they will, but they will do it all over the frame, not just at the bottom edge as in these examples.

This is NOT a cheap filter issue.

This is NOT a viewfinder light leakage issue.

This is NOT a missing lens hood issue.

This is a CANON SLR design issue - it isn't unique to Canon, but not all SLRs suffer from it!
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Its RKM

Its RKM Veteran Member • Posts: 3,135
Re: No -- that's not why you cover the eyepiece

robjm wrote:

Right. And now that I look at other shots from the series, I realize
that indeed there are additional light sources just out of frame in
this shot. Looking forward to a Canon response if it is indeed a
simple reflection issue that can be reduced - at least.

You'll be lucky. I have seen this on AE-1 images, so it is inherent in the Canon design. It isn't ubiquitous though - some SLRs show no sign of it, others are just as bad as Canon.
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Its RKM

halfamo Contributing Member • Posts: 634
Re: Strange flare with 5dII. Please check.

George, thank you for exposing this significant camera flaw.
Clever of you to suss out it's likely cause.

Have you had a response from Canon yet ?

smatty Senior Member • Posts: 2,003
Re: Strange flare with 5dII. Please check.

And I always thought, this was some kind of lens flare. I do not see this effect very often, but it happened occasionaly on my 5D and 5D MK II on varius lens and FL settings.

When I try to get a lightsource just outside of the frame (in landscape if the light is close to the bottom frame of the camera - in portrait mode, it will be the right side for me respectively) then this lightstreak appears.

Funny, that I have always mistaken it as a lens flare. But now that I know the cause, I can better try to avoid it. Although, Canon should have fixed this in the MK II....

Cheers,
Smatty

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belfox Regular Member • Posts: 259
Re: Strange flare with 5dII. Please check.

Hi George,

Lens flare, no doubt.

First things first, the options:

1. live with it (not an option, or you wouldn't be on this forum)

2. frame larger with the lights in the picture, then crop : some loss of definition (but you've got a 5DII), but mostly disturbing additional steps in the process

3. use the 40D (but you did buy the 5DII for some reason other than just your ego, I guess)

4. buy a compendium (B&H have some great stuff, look under filters, with Lee or Cokin)

The origin of your problem: the light ray that still hits the bottom part of the front lens element needs to be cut out. Turning your camera upside down limits the problem, but it still appears very slightly with the 24-105. The reason why it is not more visible than it is, is because of the asymmetrical construction of the mirror box of the camera, causing the light from the top side of the camera not being blocked.

I recreated the problem on my 5D, T90, F-1 (very old), blad, Kiev, and 5x7, using optics like 17-40L, 24-105L, 70-200L (2.8), 85/1.8, 24/2.8, 200/4 (FD), and all lenses on my mid and large formats.

Putting a compendium in front, blocking the lower light rays but not entering into the image, completely got rid of the problem in all but the most extreme cases (light source on the border of the image frame).

I also reproduced the problem on an old 300D, but it was noticable less critical to off frame light points.

BTW, Canon does know about the problem - if you take a good look at the back of your 24-105L, you'll notice a mask to block off stray rays. Canon has put it a full mm more to the center on the top side of the lens.

I always use a compendium when possible. Don't use them during wedding shootings though, since it tends to scare the s... out of people ;-p

For fun: the 24-105L is a mixed blessing. If you have your light source outside the bottom of the frame, IS on, and you "shake" your camera lightly up-and-down, you can see your flares hitting the focus screen way up in the picture frame. Veeerrryyy weird effect.

I hope this gets you off of this problem, and out shooting again.

wkr,

Geert

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Its RKM Veteran Member • Posts: 3,135
No, it definitely is NOT lens flare!

belfox wrote:

Hi George,

Lens flare, no doubt.

Not lens flare - absolutely no doubt.

First things first, the options:

1. live with it (not an option, or you wouldn't be on this forum)
2. frame larger with the lights in the picture, then crop : some loss
of definition (but you've got a 5DII), but mostly disturbing
additional steps in the process

If it was lens flare then this would actually make it worse, not better! A larger frame, cropped back would just make the artefact a larger proportion of the final image.

3. use the 40D (but you did buy the 5DII for some reason other than
just your ego, I guess)

If it was lens flare then this would also make it worse - lens flare would be a larger proportion of a 1.6 cropped sensor.

The origin of your problem: the light ray that still hits the bottom
part of the front lens element needs to be cut out.

It isn't the front of the lens that is the problem - light flaring from that area does NOT create a sharp image, as in these examples.

Turning your
camera upside down limits the problem, but it still appears very
slightly with the 24-105.

The lens is circularly symmetric - turning the lens upside down makes no difference. If rotating the lens made any difference then you would see that by rotating the lens to partially demount it. It makes no difference at all, because the problem is NOT the lens!

The reason why it is not more visible than
it is, is because of the asymmetrical construction of the mirror box
of the camera, causing the light from the top side of the camera not
being blocked.

Sheer baloney!

This is light reflecting off the back edge of the mirror. Elgeorgio has already demonstrated this himself - read the thread before spreading disinformation!

I recreated the problem on my 5D, T90, F-1 (very old), blad, Kiev,
and 5x7, using optics like 17-40L, 24-105L, 70-200L (2.8), 85/1.8,
24/2.8, 200/4 (FD), and all lenses on my mid and large formats.

Well, here's the proof for you. Take your T90 or F-1 and stick a lens - any lens - on it. Stick it on a tripod and frame it with a light so that it will cause this problem - bright light just off the bottom of the frame, ideally with a dark background. Open the back, open the shutter and LOOK from the back of the camera through the film gate at where that damned reflection is coming from!

It IS the back of the MIRROR! That IS what is creating these streaks. It is NOT lens flare.
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Its RKM

Andre Affleck Senior Member • Posts: 2,362
Re: Strange flare with 5dII. Please check.

belfox wrote:

Putting a compendium in front, blocking the lower light rays but not
entering into the image, completely got rid of the problem in all but
the most extreme cases (light source on the border of the image
frame).

I don't see how using a compendium or lens hood would work in this case. Putting anything in the light path right in front of the lens would generate a terribly vignetted edge on the image due to the fact that anything that close in the front of the lens would appear extremely OOF on the image plane. To effectively shield the light source, you would have to have the compendium just past the image edge. Since the compendium edge would be severely blurred, it would severely vignette the rest of the image.

I believe RKM calculated that you would need a 7 meter long compendium to effectively shield the sources without vignetting the image.

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