Cause of enormous flare?

[mike hardeman]

Oh, and processing is not the issue. Nor is the film. The film has 9 months before the process-by date, and is all from the same box. The processing was done by the same lab at the same time. AND there were several very good shots in that same batch, shot with other lenses.

 

I believe that is caused by a defective element, that is overexposing the center part of the picture. The reason it looks like a light leak is because this particular picture is so extreme. Several other shots simply appeared to be a couple of stops over-exposed in the center. The outlying areas of those shots were perfectly exposed with no evidence of any problem.

[Troll]

I once had a lens which developed moisture condensation on an interior element when I took it outside in the morning. Moisture on the front element evaporated right away, but it took a long time for the interior moisure to disappear.

[john_koss]

Well, crazy as it sounds, I had the exact problem once upon a time in a smaller camera.

Same exact spot, everything. All elimination testing pointed to the lens. Maybe it was or

was not flare, but it came with a particular lens (relatively modern) and that lens only.

Sunshades, cleaning, even exorcism - nothing worked. The solution was elegant and

totally effective. After careful consideration, we determined that screwing around with

defective junk was a much bigger mistake than buying the junk in the first place, so we cut

our losses and threw the lens off a bridge over I-95. The problem has never returned, so I

firmly believe that we hit upon the correct cure. Hope this helps. (PS: This is not a goof, I

am serious about having had this problem.)

Jon

[gary_deal]

Weird. More weird that you wouldn't see such an obvious spot while focusing/composing the shot, unless it only shows up when well stopped down. Setting up with a bright enough subject so that you can see the GG image at f64 might be an idea. Does the contrast seem low when focusing?

 

A bellows pinhole would tend to overlay an image on the film ("WHY is there an image of the window over my still life?"), and unless you have a light with a diffuser panel mounted with the camera, this doesn't look like that.

 

That ding might have something to do with it, if the lens is tossing light that far out the edge and the ding is on the bottom (reflecting sky?). Try a shot with the whole thing mounted upside down if you think that might be it.

 

Light reflecting from the film, back into the lens, to be reflected and sent back to the film in an out of focus spot is an unlikely possibility, as would be some sort of light leak through the shutter. Hmm, there's no chrome or other shiny/reflective surfaces on the inside of your camera, are there? Just considering ways that it would be possible to intentionally produce this effect, the right shiny plastic curved surfaces could make it happen, and only with one lens focused at the right distance.

 

The thing that really bugs me about this is that it looks an awful lot like the kind of spot you'll get if you try taking your picture (with flash) in a mirror, and that the spot itself seems taller than wider AND appears to have it's own flare, which makes it look even more like the mirror-flash thing. Odds are that you don't have some wise guy sticking a flash directly (and perfectly centered every time) in front of your lens while the shutter is open.

 

There doesn't seem to be a color cast to the flare spot, more like an overexposed area - or an average of the scene? Too bad you can't see it on the glass, else you could wave colored paper around to see where it's coming from.

 

How about this - look at the edges of the internal elements, do they have the proper blackening in place? Or did some previous owner decide that "schneideritis" was unsightly and that the offending blackening should be removed? This might create a large reflected diffuse source within the lens that could conceivably end up directly centered on the image. I knew an eyeglass wearer that had a vaguely similar problem with a high correction on large lenses. If you can see much light through the blackening it's probably inadequate. Just another idea, I'd be alarmed too.

[michael_briggs2]

I am sceptical of most of the guesses here, but one may turn out to be right. I expect that the cause won't be determined unless Michael H. can recreate the problem -- then he can start varying one (or a most a few factors) at a time and see which correlate with the problem. It may be that the cause is so oddball that Michael H. won't be able to recreate it, which won't be so bad because then he can go back to using the lens.

 

I can't see it being from a defective elements that refects light forward, and the another reflects it back to the film. Then you would see the problem in most exposures, plus it would have been visible on the ground glass for the first photo.

 

Which Schneider lens is this? It is single or multi-coated?

 

The ding doesn't look big enough nor positioned to cause this problem, but you can experiment by covering it with dull tape or paint.

[michael_veit]

Not to muddy the waters further, but is that "flair" at the top right corner of the first image?

 

To tell the truth, on my screen it looks like there's actually two bands of flair streaming diagonally down from both top corners to form the center hot spot.

 

Unfortunately, even if that's the case, I'm not sure what it would tell you except that the symmetry of that kind of formation would suggest some weird kind of bellows flair to me. Perhaps a strange combination of that particular lens' image circle and bellows extension? I guess you could test this by taking a couple different shots in constant light conditions but with shifted focus so as to see if different bellows lengths changes things.

 

I dunno, it's a puzzler!

[jan_brittenson]

I too noticed the star shape of the spot. That looks like the diffraction pattern of a rectangular hole.

 

Open up the aperture and shine a bright light through the lens. Make sure the shutter closes all the way. How cold was it when you shot? Perhaps the shutter gets a little sticky when cold and leaves a hole open.

 

Just WAGs...

[brian_ellis16]

Come on guys, it's "flare," not "flair."

[michael_veit]

Who cairs?

[mike hardeman]

I'm going to have to go over all of these theories again, so bear with me for a day or so while I do that. I'll also post one of the other images that went bad, for comparison. Again, the temperature at both exposures was in the upper 40s to mid 50s, so I don't think that it's an issue. After I post a second picture, it might make more sense.

[randy_becker]

I must admit that I haven't read all 2 million responses here but I had a thought. Well, actually 2.

 

Thought #1. It is an accidental double exposure. (Probably not but it was a thought.)

 

Thought #2: Because this is in the exact center of the lens, it might be a shutter that is intermittenly (sp?) not functioning correctly. These shutters open from the center and close back to the center. I know I am splitting hairs here but the center of the lens does expose the film ever so slightly more than the edges. Therefore I think it might be a shutter that is not closing properly every time. Obviously it is only happening every once in a while so there is probably no way to know for sure but it wouldn't hurt to have the shutter cleaned and lubed.

 

Just my thoughts,

Happy new year to all,

 

Randy

[peter_white2]

Regardless of how much the shutter is opened, all the light passing through it is focused. The shutter is right next to the aperture. So a shutter that's slightly open is really no different than a small aperture opening.

 

If we assume that Michael removed the dark slide after focusing the image and replaced it before moving the lens and/or camera, a slightly opened shutter would have only one effect: to increase the exposure.

 

It would not increase the exposure just in the center of the frame, just as an aperture of f:64 doesn't result in a greater exposure in the center of the frame than shooting wide open would, relative to the rest of the frame.

 

In fact, the opposite is the case. The smaller the aperture, the larger the image circle, and the less the light falls off in the corners.

[jon_wilson]

Don't know, but I had an experience with a similar "ghost" on a chrome and it turned out to be a light leak from a opening on the front of my lensboard for a packard shutter tube. Taped it off inside the bellows and the "ghost" left!

[sam_crater]

How's this for a theory, Michael:

 

The ghost was created when your stack of film was exposed to light due to a leak in a film box or a lapse in handling. The lighter second ghost was made by the light that passed through the top sheet of film to the second sheet.

[mike hardeman]

Sorry, doesn't wash.

 

I did some test shots and confirmed that shading the lens gets rid of this problem to a great degree. The tests ruled out light leaks because I covered any possible source of a light leak and still had the problem on that shot. But when I completely shaded the lens (to a large extent than normal), the anomoly subsided a great deal (not completely).

 

The film holders are in top shape, the camera is new, the lensboard tight. THERE ARE NO LIGHT LEAKS. I think the tendency to call it a light leak is from the extreme nature of the overexposed portion of the first image. I should have displayed an image where the overexposure was not as intense. In those images, it really looks like an overexposure, whereas the one I chose looks like someone drilled a quarter-size hole in the film holder.

[peter_white2]

Michael,

 

How do you explain the first image? Why didn't you see the anomaly while setting up the shot? It seems to me that you couldn't possibly have seen it, otherwise you would have done something to prevent it.

 

So, since you didn't see it, how could it have happened while making the exposure?

[mike hardeman]

I think one of the reasons is the fact that the film is Velvia and pushed one stop, making it more contrasty.

 

Another reason is that it was a long exposure, 2 minutes.

 

I've tried very hard to see this flare in the ground glass, it simply does not show up.

[peter_white2]

"I think one of the reasons is the fact that the film is Velvia and pushed one stop, making it more contrasty."

 

Say wuh? Michael, I'm sorry, but that's ludicrous.

 

"Another reason is that it was a long exposure, 2 minutes."

 

How would that effect the anomaly? The trees were exposed for the same two minutes. The background was exposed for the same two minutes. The relative values of the trees and background and anomaly would be the same for a 2 second exposure as for a two minute exposure.

 

"I've tried very hard to see this flare in the ground glass, it simply does not show up."

 

Therefore it isn't flare.

[mike hardeman]

Thanks. Maybe "flare" isn't the right word, perhaps "glare" is a better term. Whatever it is, it's reduced or eliminated by shading the lens. Light falling on the outer element of the lens is refracted in such a way as to produce an overexposure in the center of the picture. I'm sorry if it doesn't show up in the ground glass, but that's the way it is.

[peter_white2]

I'm just having a very hard time imagining how something could show up on film, but not on the ground glass.

 

It would be one thing if the phenomenon only occured at a small aperture and you closed down to that aperture without checking the focusing screen for the effect. But since you would have checked the screen after closing down to shooting aperture in order to be sure that you got into focus everything that you wanted in focus, and since you didn't see the phenomenon then, it's a bit of a puzzle as to how it could have gotten there.

[chauncey_walden]

Over Christmas I picked up a 1951 copy of "Lenses in Photography" by Rudolf Kingslake (then Director of Optical Design for Eastman Kodak). I just got to Chapter VI - The Brightness of Images - and therein are two example photographs that look just like yours. His explanation:

"Flare Spot - As shown in Fig. 68, any doubly-reflected light beam from a lens will cross the lens axis somewhere, and at that point it will form a well-defined image of the iris diaphragm itself. If this happens to fall close to the film plane, it will cause a more or less sharply-defined image of the iris, superposed on the middle of the picture (Fig. 71). This may be easily distinguished from the out-of-focus ghost image referred to in the last paragraph because it is precisely central, while any kind of ghost image moves about as the source is moved in the field.

If several of these multiply-reflected images of the iris diaphragm fall close to the film but not in focus upon it, their intensities may nevertheless add up to a considerable amount of light, causing a "flare spot" in the middle of the picture (Fig. 72).

A flare spot, or an in-focus central diaphragm image, is visible only at the smallest diaphragm openings, because it is usually highly magnified and at the larger diaphragm openings the image falls entirely outside the picture area. Moreover, the brightness of the diaphragm image is independent of the size of the iris, while the brightness of the background increases as the square of the iris opening; hence as the disphragm is opened, the background brightness rapidly and soon drowns the faint iris image entirely. The color of a flare spot is, of course, the average of the whole scene.

A flare spot is particularly unfortunate when stray light reflected from shiny regions in the lens mount is also present, because the two sources add up and may lead to a serious situation. Indeed, many cameras have been entirely cured of their flare spot troubles by an adequate blackening of the interior of the lens barrel."

Whew! Hope this helps.

Chauncey

[bill_proud]

That's what I said.

 

 

What?

[mike hardeman]

Chauncey,

 

Thanks a bunch for that. I think you're analysis is by far the most intelligent and closer to what I believe is going on.

 

One thing should be noted: the test shots (not shown) that I did last week confirm that this problem occurs at its worst when the lens is not sheilded. There need not be (as is the case with other lenses) any DIRECT sunlight on the outer element to see this problem. That is typical of a FLARE.

 

In this case, what is seen in all of the troublesome images is merely an overexposure of the central area. You do not see the typical image of the leaves of the iris, as is the case with a flare.

 

So, even in the best of situations, you have an area that is slightly over-exposed in the middle. When the light source is directly behind the camera, this over-exposure is at a minimum and is barely detectable.

 

I wonder how practical it is to blacken the inside of the barrel of this lens.

[peter_white2]

Michael,

 

For the last time, if it's flare, why didn't you see it when viewing the image on the ground glass?

 

Perhaps there's something you haven't told us? Perhaps you didn't look at the image after you stopped down? Hmmm?