Large Format uneven exposure problems with 4 x 5 negative using 90mm lens

I am experiencing some problem with my negatives - which I have shot with a Sinar F1

camera using a 90mm Rodenstock Grandagon 1:6.8 lens. It appears that one side (i.e.

right or left) of the image is noticeably a shade darker - even a little bluer than on the

other. This is annoying as it occurs where I have composed face on and the tones should

therefore be even throughout and it is the negative that appears to be at fault not the

enlarger. This could be explained by reflected light when shooting - except that this

problem affects the sky as well as the terrain (I am shooting landscape). I have taken my

lens to the retailer and shown them the images, they seemed perplexed as to what is

causing the irregularity. I would like to know if anyone else has ever had this problem and

what was the cause. Is it a fault with the lens or could I be doing something incorrectly?<div></div>

You have the need for a "center filter". The whole center is hot(overexposed).

Isabel,

 

Funny thing is... some people like the look and will even burn the edges in during the

printing process! Not my cup of tea though. :)

 

But, I agree with Steve. You need a center filter...

 

So, no, you're not doing something incorrectly... just the nature of the beast!

 

Cheers

Check that the standards are aligned - if they are shifted (front to the right or rear to the left), the center hot spot will move to the left and sides will have uneven exposure. A center filter will solve the hot spot and uneven exposure altogether; carefully zeroing all movements should place the hot spot dead in the center of the frame and all sides should have about equal exposure. You may also want to check that the lens alignment on the lens board is correct.

I have doubts that the problem is a lack of a center filter. The problem seems to extreme for the non-uniform illumination that I'd expect from a 90 mm lens on 4x5, unless Isabel is using the lens near wide-open. The other reason is that the right side seems distinctly worse than the left, as Isabel points out. Also the bottom seems underexposed, but not the top. Isabel says that she composed face on, which I understand to mean that she used no movements. Is that correct? So the illumination falloff should be symmetric about the center of the image, with a radial falloff about the center.

 

Peter's suggestions to check that you don't have any intended movements are good.

 

Was the film transparency or negative?

 

Could there be some problem with the uniformity of the development? Perhaps try a different lab with one film.

 

Have you tried taking a photo with a longer lens to see if you get an even exposure?

 

Here's another test: focus the lens at infinity, then take a photo of a nearby, uniformly illuminated surface, such as a wall or a poster board. This will show the illumination pattern without the distraction of a non-uniform subject.

Did you load the film correctly ? looks like your film was not loaded flat.

I don't think this is a camera issue at all. I think it came from the film processing. Did you have this sheet processed with others that were made with a different lens? If so, do they show the same uneven character? Take another shot with the Grandagon and process it, and see if you still have the problem. I'd be willing to bet that the lens and camera, and your shooting technique, are fine.

 

Don't be surprised if a retailer can't figure this one out. A few years ago, I had a shot form a Rollei TLR with a weird bright streak running through one frame. My local camera shop assured me that it was a shutter problem, and had me pay over $100 for a dubious CLA. Later, I looked closely at the whole strip of negatives (which the shop had looked at when "diagnosing" the problem) and realized that what caused the streak was a static electricity discharge inside the camera. Not surprising, considering I was on top of a New Mexico mountain in the winter. I can't belive they couldn't figure out what the real problem was.

It looks like you used a lot of front fall. Did you? And did you shoot at, say F/8? I've put in the view from the finder with contrast enhanced so you can see the circle of coverage better.<div></div>

Make that front rise.

What about the wrong condenser and lens combination in the enlarger ?<p>Just for yucks,

try shooting a 4x5 Polaroid test shot with a 545 or 550 film holder and see if the problem

persists. Then you'll know if it's the Grandagon lens, although it seems doubtful to me that it

would be.....

It looks to me as though the image circle of the lens is not covering

the film plane when focused at infinity and the CORRECT center filter would solve the problem. To check this make an exposure with two stops

extension. That is, find a subject for closeup and set the bellows extension at 180mm (90mm X 2). Move the camera to focus. When you set the exposure be sure to open the lens 2 stops more or the shutter speed 4 times longer to correct for the extension. If your exposure time is greater 4 seconds you should add another 25% for reprocity and more if the exposure time is longer. This will place the "sweet spot" on the film plane and make the image circle larger. If there is even exposure into the corners the problem is the lens.

Isabel, tell us what the aperture was that you used to take the picture.

This lens has been recommended before on this forum. Rodenstock specs it to easily cover 4x5 -- the circle of coverage is given by Rodenstock as 221 mm diameter -- see http://www.linos.com/en/prod/grandagon-n.html. The PDF datasheet includes a graph of the illumination from this lens. At f11 and the corners of a 4x5 film (76 mm radius), the illumination falloff should be approximately 1.4 stops -- even better at f16. On the right side, Isabel's photo shows substantial darkening starting by 45 mm from the center. At apertures of f11 or f16 or smaller, there should only be a 30% falloff by this point. I don't think the cause of this uneven exposure is the lens, unless the lens was used near wide open. (This is assuming no movements.)

 

This is why I wondered about the development, and suggested experiments of trying a longer lens and a different lab.

Noah Schwartz: "What about the wrong condenser and lens combination in the enlarger ?"

 

Most excellent posit! I will second it. Given how many processing places have no adequate hardware for 4x5, I think it's quite feasible.

 

Good show, Mr. Schwartz.

Isabel wrote "and it is the negative that appears to be at fault not the enlarger" though it can be hard to judge negatives. This might be a reason to do a transparency, or to do the experiment that I suggested in my first post.

 

I suggested taking a photo of a uniform wall, out of focus. The idea is to better determine the pattern of the non-uniformity. If it is due to the lens, it should be rotationally symmetric about the optical axis, depending only on distance from the optical axis. If it is from the development, the pattern will be different. A negative without a subject will be easier to judge without the extra step of the enlarger.

 

Other things I have thought of would tend to lighten the edges: light leaks, reflections in the cameras, ...

I don't know what the problem is, but let me say what I do know.

 

I have a f/6.8 90 mm Grandagon-N, and it is a fine lens. Occasionally, with Portra VC 160 negative film,I see both a drop off of intensity from center to the sides and also a shift in color, but I've never seen anything as extreme as in your example. I scan rather than print with an enlarger, so I don't know if enlarging would exaggerate the problem, but it is certainly not apparent just looking at my negative. I've taken to using a center filter in scenes in which there is a potential for a problem, but in most cases I probably don't need it.

 

In your example, from the shadows, the sun appears to be on the right and a bit behind the camera. In a case like that, you might see a difference between right and left, but you would expect the lighter sky to be on the side with the sun. In your case it is just the opposite.

 

Finally, it does appear that the foreground on the left is out of focus. That suggests either a slight swing or tilt, but I don't see how that could produce a asymmetric illumination from left to right.

This problem aside, I would recommend checking that the standards are parallel.

Do you have a bellows-type lens shade? If the shade is not evenly compressed it will cause this type of uneven illumination. It might be the position of your standards, but they would have to be seriously out of alignment, so much so that on one side it would have to be extended approximately longer than the focal length of the lens, but well within that extension on the other side.

I used an aperture of f45 which is the highest aperture on this lens - in order to get

maximum depth of field. I did not tilt or shift the standards in this picture - they were

square on and aligned, ie parallel to each other, but the whole camera was facing in a

downward direction toward the ground in order to focus on the foreground. The

suggestion that one side is out of focus is inacurate - the actual negative or print is in

focus - an illusion on the computer I think. What is most annoying about this problem is

that it does not affect every picture that I shoot.

 

I am currently completing a project for BA in photography and this is one of my sequence

of images, most of which are shot with the 90mm succesfully, and a small number using a

150mm which so far I have not experienced this problem with.

 

Many thanks for all your suggestions.