Detecting flare

Marco B · Jun 28, 2009

Hi all,

Since I shoot a lot of night shots, I regularly have to deal with potential flare problems. Now although I have become quite good at avoiding these by carefully composing the images, there are still sometimes situations where it is difficult to judge.

For example, in this image:

http://www.boeringa.demon.nl/haarlem_by_night/slides/DN1_0236_3.html

I was aware of the strong light on the right, but after adjusting my camera, I couldn't see any sign or effect of flare through the viewfinder at all... Now luckily, in this particular image, I am not bothered at all with the flare, but there can be different scenes that are ruined by such a flare.

Now the answer is probably going to be no, but is there any reliable and fault prove way to detect flare before pressing the shutter? :confused: I have read about the depth-of-field preview as one way to more easily detect potential issues, but are there any other ways to reliably detect a situation like in the image above?

Marco

ic-racer · Jun 28, 2009

Since you did not see it in the finder (SLR I presume) that may be caused by light reflecting off of something in the light path behind the mirror (edge of the film frame?). Instant film to check?

Marco B · Jun 29, 2009

ic-racer said:
Since you did not see it in the finder (SLR I presume) that may be caused by light reflecting off of something in the light path behind the mirror (edge of the film frame?). Instant film to check?

Yes, it was SLR. You may be right. It is a very particular situation with a strong light source only just outside the frame. Especially in this situation, I have seen very long flame like flares like in the example, occur. I am not exactly sure what causes them, but like you suggest, it might well be a different mechanism from the "normal" flare caused by reflections on the aperture blades or reflections related to the glass elements of the lens. I did use a lenshood.

I have seen a similar type of flare happen with some of my LF shots too... again with a strong light source only just outside the frame.

pgomena · Jun 29, 2009

Stopping down the aperture will help detect flare. You have a lens hood, so that's taken care of. Do not use a glass filter of any kind in front of the lens is my next advice, and, if there is a strong light source off to one side, stand between it and the camera (if possible) to shield it from any stray light. In flare situations, I try to keep light from striking even the inside of the lens shade. (This has resulted in more than one picture with part of my hat in the frame.)

Peter Gomena

Marco B · Jun 29, 2009

I also read the tip about black felt inside the lens hood, but don't know how effective it is compared to the dark grey plastic of the lens hood. Anyone have experience with this, and where do you buy black felt?

David A. Goldfarb · Jun 29, 2009

I've bought black flocking paper from scientificsonline.com (Edmund Scientific), and it does improve the effectiveness of a (solid metal or plastic) lens shade. In this case, though, you might need a compendium shade that you can adjust to just short of vignetting to keep stray light outside the frame from causing flare.

Q.G. · Jun 29, 2009

I begin to think that these bright sources can find a spot where a longer shade is needed (to block them from the field of view of the lens - which is slightly larger than the field captured in the format's frame, i.e. the light enters the lens even though the source is just outside the frame), yet where such a longer shade would already vignet when long enough.
I.e. a spot where petal shaped shades are better than square ones.

But i may be totally wrong. Have had it on my to-do list to test (adding semi-circular flanges to the sides of the square shades), but like so many other things too haven't come round to actually doing it

What would you say? Silly idea? Or worth a try?

P.S. i have had such flares spoil frames when using a compendium shade set to the proper length too. Very annoying, when you think you have taken every precaution, and still there is that blob of light.

bsdunek · Jun 29, 2009

Something I read years ago about field of view of a lens changing depending on the aperture. I think it had to do with this very problem. The lens has a wider field of view than the film gate, and a flare outside the film view can still affect things. If the field of view widens with smaller apertures, this may be what happened. When putting bright lights just outside the field of view, try manually stopping down to see if a flare show up.

Anyone else remember this phenomena?

Ian Grant · Jun 29, 2009

You can also mask the lens hood, as they do with cine & high end video camera lenses. I had a Hoya 28mm that flared horrifically and this worked well.

Ian

Q.G. · Jun 29, 2009

bsdunek said:
[...] Anyone else remember this phenomena?

Yep.
The smaller the aperture, the smaller the field of view, the longer a hood may be.

The field of view also changes a bit when you focus a lens. So a hood may/should be longer when the lens is focussed closer.

There is a patent describing a camera system that has an 'intelligent' bellows shade, that is fed info about focal length, focus (and aperture), and then adjusts its length accordingly.
Never been build though.

Marco B · Jun 29, 2009

Q.G. said:
I begin to think that these bright sources can find a spot where a longer shade is needed (to block them from the field of view of the lens - which is slightly larger than the field captured in the format's frame, i.e. the light enters the lens even though the source is just outside the frame)

This is actually a very good point! As I shoot LF too, the concept of the usable image circle of a lens is not alien to me. And even in SLR, the image circle of the lenses is slightly larger than the actual image projected on the film. This is especially so for the longer site of the frame (36mm), there will be a larger unused part of the image circle there. So when shooting vertical shots, as I often do and also in the shot above, the chances are probably bigger that you miss a flare source to the right and left of the frame, again as in this case on the right.

So, like you suggest, the flare might actually be caused by light hitting the lens in a part that will NOT project onto the viewfinders mirror, so you will never really be able to detect it in the viewfinder, but it might hit just outside the frame in the back of the camera body and cause a flare due to a strong reflection inside the camera.

Martin Aislabie · Jul 2, 2009

If I am aiming the camera any where near the sun or other bright light sources, I always go round to the front of the camera and check for direct light falling across the front element and/or filter.

Of course the camera needs to be tripod mounted :rolleyes:

Its easy with the sun - the shadows are distinct, but you can do it at night with a little care.

At night when I am at the front of the camera and looking directly down the barrel of the lens, I use my hand a lens shade - you can see the shadow your hand makes reasonably easily.

I can then use my Ground Glass Protector as a Flag for the lens

There are times when it just is not possible to shade the front element - when the light source is right at the edge of the frame - but at least you know before you choose to shoot

Martin

Detecting flare

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