Differences in Contrast on a Roll of 35mm Film

[FilmOnly]

Hello, all,

I enjoy 35mm photgraphy, and, in fact, this is my only format. I have noticed, though, that some frames--on the same roll--appear to have notable differences in contrast, and perhaps sharpness, too. Let me be more precise. These differences are observed under almost identical conditions: same lens, same camera, same location, similar time of day, and similar aperture (not varying by more than 2/3 of a stop). Since this is the same roll of film, processed by the lab I have used now for about two years, I am a bit puzzled. I would have thought that, for example, frame 5, shot at 1/500th and f/8 would have similar contrast to, say, frame 9, which was shot the next day, at the same location, at 1/500th and f/6.3 or f/7.1 (all metered with a hand-held meter). I have also noticed that the one that has less contrast also looks a bit softer, too.

Any opinions on what I am seeing? If it helps, I note that I use a pair of Nikon FEs, and use the 105/2.5 non-AI on a fair amount of my shots. Both cameras have been recently CLAed.

 

[Ian C]

Possible Lens or Filter Flare

The image recorded on film is due to: film, lens, (and any filters on the lens), and the light present.

If truly nothing else changed then I’d consider lens flare. In particular, is it possible that the view angle of the lens on the problem frames allowed a straight line from the sun to the front surface of the lens or filter?

This is still a problem even if the sun is outside of the viewing angle of the lens. All that’s needed to flare and kill contrast is strong light that intercepts the lens or filter at an angle outside the lens’s field of view.

This can be exacerbated by any fingerprints, hazing, or greasy film on any of the surfaces of the lens or filters—the “dirty window effect”—such as we see when driving an automobile. The window looks clean when the light is indirect, but let the sun graze the front surface and the glare makes it difficult to see through.

Making sure that the lens and filters are clean is a first step to correcting the problem. Don’t neglect cleaning the rear surface of the lens as well. The use of the correct lens hood to shade the lens from the direct sun will help ensure that the image isn’t affected by strong flare.

I like to get off to one side of the front of the lens and sight towards the sun to see if there is a straight line between the front of the lens or filters and the sun. If so, I’ll hold a gray card off to the side to shade the lens so that the sun can’t fall directly on the front glass.

Other than lens flare, I’m not aware of anything else that could cause a uniform loss in contrast over the entire frame. For example, light leaks, leave a definite pattern that is strongest near the point of entry.

 

[Markster]

Very interesting. Would a polarizing filter or perhaps a UV filter cut down on that, or would you still need to be wary? I always thought if you can't see the sunspots on the picture you were safe. Never thought it might change contrast etc.

 

[Ian C]

Very interesting. Would a polarizing filter or perhaps a UV filter cut down on that, or would you still need to be wary? I always thought if you can't see the sunspots on the picture you were safe. Never thought it might change contrast etc.

These filters wouldn’t help. What’s needed is to make sure that the exposed glass is clean and shaded from a straight line between these surfaces and the sun or other very bright light source. Even brilliant, mirror-like reflections of the sun from water or glass surfaces like those we sometimes get from mirrored glass in modern commercial buildings can create troublesome flare.

 

[Ian C]

Think of it this way. If the front glass is spotless and sunlight outside of the view on the lens strikes it, there might be little discernable flare. But let the front glass have any film of hazing or fingerprints and the flare can be significant—just like the difference between a clean automobile windshield and a dirty one.

 

[boswald]

It would help if you could post a pic of the negs/a contact sheet.

 

[FilmOnly]

I very much appreciate the replies--thanks.

I would post the photos, but I do not have a scanner.

I went back to the site today, and noticed that the barrier of trees (even though it is winter) may perhaps alter the lighting. I have observed good contrast when my subject, a train, was on the near track--near the trees--and so-so contrast when my subject was on the adjacent far track, which is a tad further from the trees and in more sunlight. I did not (and still do not) think there would be more than a half-stop difference between the two tracks, but I suppose I could be wrong. It is difficult to get to the other side (the far track) in order to take a reading there.

With regard to the issue of shooting into the sun, I note that I rarely even come close to doing this, and in the said location the sun would not seem to be presenting this type of problem, especially at the time I took the shots. Also, the shots were taken on partly cloudy days. I used 400 speed film.

 

[Rol_Lei Nut]

Shutter problems could also cause what you describe, though you mention that both cameras were CLA'd.
While unlikely, especially if you're dealing with two bodies, I have occasionally received cameras back from services or CLAs which were less than perfect...

Other candidates could be light leaks (even a CLA can easily miss one), or perhaps a film cassette left in the sun. Also an exposure compensation forgotten "on". Lab error *is* also possible: even the best sometimes mess-up... ;-)

 

[2F/2F]

Sounds like the lighting was different.

 

[Christopher Walrath]

One more idea. Are you comparing negatives? If so then it almost has to be on camera as the roll is processed uniformally (in theory). Or are you comparing prints? In which case, the fault could be through the printing of the negs if the negs show no discernable difference. Tough to gues without a visual reference.

 

[tkamiya]

Are you sure you are seeing difference in contrast not just difference in density? Half a stop difference in exposure will create quite a significant difference in negative density that could easily be mistaken for difference in contrast. Also, since this test wasn't done in controlled environment, it may be very difficult to judge difference in contrast - and further ensure that each exposure was done close enough to each other.

 

[markbarendt]

I normally shoot manual and meter once for a situation.

I have a roll where I was shooting a parade mid-day, metered for the darkest shadows and started shooting, no lighting change, shooting most everything looking North North East.

I was surprised when different frames printed best at different paper grades.

The only things that really changed were the subjects.