Puzzling light blocking. Vignetting, lens hood? Please help to identify the source.

[Vic Montaigne]

Hello to everyone!

In a series of shots taken last year all came out just fine except for four consecutive shots, 2 identical exposures for each of 2 images. They show a broad stripe of blocked light (white in the negative, black in the print), 3 of the stripes being pitch-black across the top (of upright image), the first stripe however of similar width, but on the bottom end and not completely black but somehow like horizontally pleated.

I am not absolutely certain I can rule out a developing issue. But I think so, as these four negatives were developed in a batch of six in a MOD54 tank, the other 2 negatives being fine. All four shots were taken with a Schneider SA 5,6/90 and lots of rise (first image and backup 44 mm, second image and backup 46 mm). The lens allows for 47 mm in portrait mode, so that was quite close to the limit. F-stops were 33 2/3 in the first two shots, 22 1/2 in the two following shots.

I cannot swear if I had the Lee Wide Angle Lens Hood mounted, but I think I did so routinely, mounted with a wide angle adapter ring.

So, what possible mistakes would be capable of producing such phenomena?

If it was lens vignetting, caused by exceeding the image circle, shouldn't there be some round corner vignetting instead of a stripe? Also, I tried the same setup at home under well-lit conditions. Checking through the GG corners, I could not find any signs of vignetting at the apertures used. (Without rise no vignetting from f 11, with rise of 44-46 mm no vignetting from f 22.)

Second possibility, would a black stripe be consistent with blockage by the lens hood, wrongly adjusted? While checking the corners the Lee Wide Angle Lens Hood shows up only when fully extended (which I can rule out) or when in oblique position. The latter would have been possible. If I was in a hurry, e.g. because of fast approaching dark rain clouds, I might have inadvertently touched and turned the hood after having checked for vignetting. Or I might have had difficulties in checking due to light conditions.

I would love to pin down the cause. If I have simply exceeded the movement possible with this lens I would consider exchanging it for a SA 90 XL, although this would pose other problems with the TK 45s I used. At the occasion the four shots were the only ones I made with the SA 5,6/90. For all others I used the 72 XL, 110 XL, 150 and 240 lenses. This might be coincidence, but then it might not.

Image circle, lens hood or something else, what can cause broad black stripes?

Thanks,

[djdister]

You really need to post some photos or scans of the problem.

[ic-racer]

Shadows from bellows, lens hoods, filters etc, that can spoil a negative need to be observed on the ground glass at working aperture. Maybe you need a better dark cloth?

[Bob Salomon]

Are you using Riteway holders?

[Vic Montaigne]

Bob, thanks for responding. No Riteway holders are involved, mine are all Fidelity Elite holders. After exposure I pull out the dark sheet completely, turn it to mark exposure and then reinsert it.

(If I may I would like to ask you a question concerning the SA 90 XL mentioned in my post as a possible alternative for the SA 5,6/90. It is from one of your posts that I learned that the SA 90 XL will not pass the opening of the TK 45s' front standard. Will the version with removable rear flange pass? According to Schneider specs the diamater is 86 mm with flange, 78 mm without. I measured some 83 mm for the TK opening. So it should be a tight fit but possible. Would you know for sure from experience if it will fit with the rear flange removed?)

[Bob Salomon]

Bob, thanks for responding. No Riteway holders are involved, mine are all Fidelity Elite holders. After exposure I pull out the dark sheet completely, turn it to mark exposure and then reinsert it.

(If I may I would like to ask you a question concerning the SA 90 XL mentioned in my post as a possible alternative for the SA 5,6/90. It is from one of your posts that I learned that the SA 90 XL will not pass the opening of the TK 45s' front standard. Will the version with removable rear flange pass? According to Schneider specs the diamater is 86 mm with flange, 78 mm without. I measured some 83 mm for the TK opening. So it should be a tight fit but possible. Would you know for sure from experience if it will fit with the rear flange removed?)

Yes, that version will work. It is the reason why Schneider had to redesign the rear group.

Many of the later holders made by Fidelity/Lisco did not seat properly in the Linhof back and would feel like they were fully seated when, in fact, they were about ½ an inch from seating fully. This created a strip like you are describing. After a dozen or so insertation and removals this problem disappeared.
It could also be eliminated by lightly running a file over the sharp ridges in the light trap area of the holder. Could this be your problem? It was pretty common when Fidelity was still in business making holders but has not been very common over the past decade or so. It was so bad at one point that I had to visit their offices in CA to see what was going on and how to solve it. Apparently their older molds for the holders were worn out and they re-tooled without checking Linhof's specs. But since they were part of the group that owned Cambodia maybe they didn't worry about brands with tighter specs.

[Vic Montaigne]

Thank you for this valuable hint. I take it that the "light trap area of the holder" is the area at the bottom end when inserted. Please correct me, if I got you wrong. I have just identified and inspected the two holders in question and could not find anything that caught the eye. One of the holders has been used before without problems.

However, you are right in that it IS a very tight fit. In general I tend to use force cautiously, accordingly I find it quite conceivable that at some point I happened to stop short of complete insertion without noticing. The fit is really tight and the spring of the back very strong. Be assured, from now on I will take special care to thoroughly insert the holders. Thanks again for reporting the story!

Case solved I hope. However, should anyone be aware of other possible causes for a broad black strip on top (bottom in camera) please let me know.

[Bob Salomon]

Thank you for this valuable hint. I take it that the "light trap area of the holder" is the area at the bottom end when inserted. Please correct me, if I got you wrong. I have just identified and inspected the two holders in question and could not find anything that caught the eye. One of the holders has been used before without problems.

However, you are right in that it IS a very tight fit. In general I tend to use force cautiously, accordingly I find it quite conceivable that at some point I happened to stop short of complete insertion without noticing. The fit is really tight and the spring of the back very strong. Be assured, from now on I will take special care to thoroughly insert the holders. Thanks again for reporting the story!

Case solved I hope. However, should anyone be aware of other possible causes for a broad black strip on top (bottom in camera) please let me know.

Just rub those sharp edges of the holders with a file or sandpaper to round the edges off a bit and that will solve the problem.

[Michael W]

What camera?

[Vic Montaigne]

@Bob

Just rub those sharp edges of the holders with a file or sandpaper to round the edges off a bit and that will solve the problem.
I will check the whole bunch and smoothen the edges where appropriate. Thanks for pointing out.

@Michael W

What camera?
As mentioned before the shots were taken with a Linhof Technikardan 45s (abbr. TK 45s).


EDIT of my post #5: I of course do not pull the dark slide after exposure but before. Otherwise images would show even more light blocking...:cool:

[Willie]

Might check for bellows sag or folds getting in the way.

[Vic Montaigne]

Hi Willie,

You are of course right. I had thought of this possibility. However, when putting together the same setup of camera, lens, movement, bellows and lens hood for the sake of finding the cause, I could not make out any sagging of the bellows.

How/where would it show? On the GG, when checking for vignetting through the GG corners, or both? I might well have overlooked it in the situation, but should sagging not show again with the same setup in place?

Does sagging show in any way different when a lot of rise is applied? (Sorry, I am better at visualizing images than the physics of light rays at work...)

[Maris Rusis]

...Does sagging show in any way different when a lot of rise is applied? (Sorry, I am better at visualizing images than the physics of light rays at work...)

Ordinary bellows vignetting due to sag cuts off the bottom of the picture = top of the ground glass image. With extreme rise the bellows can cut off the top of the picture = bottom of the ground glass. Bag bellows when available is a cure. Pulling several of the top front pleats of an "accordion" bellows toward the front standard can help prevent cut off with extreme rise. I always look through the lens (at working aperture) towards the ground glass to check for vignetting. If I can see all of the ground glass it can see me and all of the field of view.

[Vic Montaigne]

Hello Maris,

thank you for your very helpful answer.


Ordinary bellows vignetting due to sag cuts off the bottom of the picture = top of the ground glass image. With extreme rise the bellows can cut off the top of the picture = bottom of the ground glass.
This is exactly the kind of knowledge that would be very difficult to find in books. Thanks for the information, much appreciated!


Bag bellows when available is a cure. Pulling several of the top front pleats of an "accordion" bellows toward the front standard can help prevent cut off with extreme rise..
I will keep in mind your advice concerning the front pleats.

Talking about the ruined shots, I am quite sure that bag bellows were mounted, simply because with this camera/lens combo and standard bellows it would have been impossible to raise the front standard that high. Usually I lightly pull at the four corners of the bag bellows to make sure nothing will get into the way. But inmidst of the sophisticated LF-routine, which is not yet a real routine to me, it is still a possibility. I might have forgotten.


I always look through the lens (at working aperture) towards the ground glass to check for vignetting. If I can see all of the ground glass it can see me and all of the field of view. Me too, I prefer this direction for checking, at least with wide angle lenses. But - have you ever tried to stick your head into a compendium-like lens hood and twist your neck to try and make out the corners? ;)

[Maris Rusis]

.... But - have you ever tried to stick your head into a compendium-like lens hood and twist your neck to try and make out the corners? ;)
Ah, compendium lens hoods. I love 'em and I hate 'em. And I think I've vignetted more negatives with bad hood adjustment than with saggy bellows. These days I don't put my eye in the compendium hood when looking for the ground-glass corners. I move further back from the front of the camera and look past the edges of the hood to make sure those edges aren't obstructing some of the picture. To make things easier to see I'll use the focussing cloth over the front of the camera. Admittedly this looks rather odd but works well.

[Vic Montaigne]

Maris, I am not sure I fully understood your technique. But you are right, when stepping back a little I actually manage to see the cut out corners even with the lens hood attached, although this gets more difficult with a stopped down lens and lots of rise.

There is however something that I do not yet understand concerning the two methods of checking - back to front vs. front to back. In forums I read more than once that this would always be vice versa, mechanical vignetting would always show in both directions. Yet I get different results:

I repeated the following many times because I just could not believe what I saw. When I check for vignetting with the SA 5.6 on the TK 45s, with bag bellows, with or without rise, at full aperture, looking from the back, I can most definitely make out that football or lemon shape of the lens opening, transforming to a round shape when stopping down. However, at the same time, when looking from the front through the lens, the cut out GG corners are freely visible at all apertures. Looking straight along the optical axis all one can see is of course a patch of the GG. Looking from different angles though, one can see each of the corners at some point when moving around. According to the understanding I had to this day this should not be the case when at the same time I see vignetting from the back. Have I got something wrong here?

On the other hand, if I stand in front of the camera, this time not looking for the corners but simply onto the lens opening, I can again see the football shape as soon as I am looking from any other angle than along the optical axis. By stopping down I get to see the actual blades and the round (or really polygonal) opening they form. Only problem, how would I know to what degree of wide angle my perspective needs to shift to be sure there will be no obstruction? I hope you know what I mean.

Could someone please explain to me which method of checking for mechanical and or optical vignetting is reliable under all circumstances! I know the one from back to front is, but, with very wide lenses and very high rise at small apertures this becomes really really difficult. An alternative would be very welcome. (By the way, photographer bent down low, twisted awkwardly, looking up to the back of the camera is a sight no less peculiar than the dark cloth over the front ;)...).

[Maris Rusis]

I'm afraid there's no easy way. A closely adjusted compendium lens hood that doesn't vignette at full lens aperture will almost certainly vignette strongly when the lens is stopped down. For example I can line up by eye (from in front of the lens) the right hand edge of the compendium with the left hand edge of the oval shaped (fully open) lens entrance pupil and the left hand edge of the ground glass. When the lens is stopped down the edges of the oval entrance pupil move inward and form a small round hole. The original line-up is lost and the result is vignetting.

The compendium hood must be optimised with the lens at working aperture. This is difficult because the aperture may be tiny, the ground glass might be dark, and the "looking" angle might be very oblique. In the studio I could have an assistant hold a Light Panel (Cabin CL-5000P for me) against the camera ground glass to make the corners bright enough to see through the stopped-down aperture. In field work I've abandoned the compendium hood and just shade the lens with my hand, hat, or dark-slide. This works ok but I have several negatives with hands, hats, or dark-slides just showing on the edge.

[Vic Montaigne]

I do not want to overstress your readiness to help, so I will try to sum up:

Checking for vignetting:

Like described above in # 16, looking front to back - spotting the cutout corners of the groundglass through the lens (no lens shade involved), produced a different result than looking from back to front the conventional way, that is through the cutout corners to the lens opening: Checking from back to front showed vignetting at full aperture, the lens had to be stopped down for a round opening. However, viewing front to back allowed for free vision of all four corners of the ground glass already at full aperture, without having to stop down the lens. This is an obvious contradiction. Maybe it occurs only under certain conditions, I have no idea. Should someone have an explanation for this I would be glad to hear it.

Otherwise I will just stick to checking through the open corners of the ground glass as described by Leslie Stroebel (View Camera Technique, 7th ed, p. 108). Even if this tends to become very difficult with wide lenses and extreme rise.

By the way, according to Stroebel stopping down the lens reduces both, vignetting by lens barrel and by lens shade. Usually never miss them, yet I wish I could verify any of this immediately using digital or polaroid...

What I have learnt regarding my four ruined negatives:

The first one (obstruction displaying some kind of pleated pattern at bottom of image) might have been caused by the compendium style lens shade which I had forgotten to adjust properly but have corrected following this exposure.

Light blocking in the three following images (pitch black broad stripe at top of image) might have been caused either by the holder issue described by Bob, or by interference of the bag bellows, gone unnoticed. I will certainly put increased attention to avoid those potential mistakes.

Many thanks to everyone who took the time to contribute!