Teach me to see soft corners...

[Tim Meisburger]

Why am I constantly surprised by soft--or non-existent--corners in my negatives? I don't use extreme movements much, but when I travel I often shoot what's available, and that is often architecture. I just came back from a business trip to the US an have several negative that, but for soft corners, would be nice. In one, I had an old mission church with a fence and gate. The gate and front door were not aligned in reality, but sneakily I used shift (I never use shift) to line them up and make a pleasing (or boring) symmetricallity (is that even a word?). Bam - I develop the negative and the whole upper left corner is gone. Why don't I see it? And how can I improve my technique so I do? (I'm already plotting to replace my lenses with some with better coverage).

Thanks for suggestions

[djdister]

How confident/cognizant are you of the parallelism of your front and rear standards? Unintentional tilt or swing (or both) can lead to soft corners. If two adjacent corners are soft, it could just be off from one camera movement (i.e. tilt), but if only one corner is soft, or opposite corners are soft, then you have affected two planes (tilt and swing) at the same time.

[Tim Meisburger]

Unless I have forgotten to zero after a tilt (I did once), I don't have problems with parallelism. My problem seems to be seeing what is plainly on the ground glass in front of me. Maybe I need one of those square loupes to look in corners, but I suspect I just need to focus (my mind) less on the subject and more on the corners.

[Mark Sawyer]

Tim, I'm not sure if your camera's ground glass has clipped corners or not, but that's what they're there for! Peek through each corner and see if you can see the whole aperture opening at the shooting f/stop. If you see the whole aperture, you're good; partial aperture circle and you're into partial illumination; no aperture visible, no light hitting the corners.

[Old-N-Feeble]

It's possible the front or rear standard is moving between the time you compose and make the exposure... perhaps the rear standard when inserting the DDS? How sure are you the movements all lock solidly? Is it possible the GG isn't seated properly?

[Doremus Scudder]

Tim,

First, and something I don't see mentioned very much, is that when you use movements, stopping down will often get you less coverage than when viewing wide open. This occurs because, when wide open and using, say, lots of shift or rise, the farthest corner gets fairly well illuminated by the part of the lens aperture opposite it and farthest away (I hope this is making sense...). When you stop down to taking aperture, this side of the aperture basically goes away, leaving the corner in the dark. This what I suspect to be your problem.

A similar thing happens when using filters in front of the lens; stopping down can often lead to vignetting from the filter ring.

So, when setting up a shot like this, you need to remember to check with all filters in place and with the lens stopped down to taking aperture. (Reread the previous sentence for emphasis).

Check by either looking through the clipped corners of your ground glass and making sure you can see the entire lens aperture, or, by looking back through the lens aperture and making sure you can see all corners of the ground glass. If you can't, you'll vignette.

As far as "soft corners" go. Most modern lenses are mechanically vignetted so that if you have coverage, you'll get a relatively sharp image. Older lenses, however, often have a larger circle of illumination than sharp image circle of coverage. If you're using older lenses (even some of my Ektars are really soft at the extremes), you'll just have to shoot with that awareness. A soft corner in a dark blue sky makes little difference, but if there is important detail there, you may want to reconsider.

At any rate, if you think you have lenses that are soft at the extremes of coverage, you'll have to check the sharpness on the ground glass at the taking aperture, and then later on the neg itself till you get a feel for how much you can stretch coverage for a particular lens.

Hope this helps,

Doremus

[Tim Meisburger]

Thanks Mark. That makes sense, and explains why you get greater coverage as you stop down (as the aperture moves towards the centre there is less mechanical vignetting from the lens barrel). Slowly I figure this out.

I'll have to practice checking the corners and including that in my normal routine. (plus buy lenses with more coverage).

[Tim Meisburger]

Thanks Doremus, that explains even more. So the whole glass can look illuminated at 6.8, then I close the lens, insert the holder attach a yellow filter, then stop down to 45 or 64, and at this point I am introducing mechanical vignetting from the front of the lens. Interesting, and illuminating.

[Doremus Scudder]

Thanks Doremus, that explains even more. So the whole glass can look illuminated at 6.8, then I close the lens, insert the holder attach a yellow filter, then stop down to 45 or 64, and at this point I am introducing mechanical vignetting from the front of the lens. Interesting, and illuminating.

What can happen is that the corners are mostly/partially illuminated when the aperture is wide, but a smaller aperture just doesn't "see" the corner of the film. Try shifting to an extreme and then look through the front of the lens at a corner as you stop down and you'll see what I mean. Filters can make things worse, but even without one, you can clip a corner pretty easily if you forget to check when using extreme movements. I make the mistake every now and then myself when I'm not paying enough attention, so don't feel bad.

Best,

Doremus

[Dan Fromm]

Doremus, I'm sorry, but I don't agree with you about the effect of stopping down on mechanical vignetting.

I hang some of my lenses in front of a leaf shutter, so am always at risk of mechanical vignetting by the rear of the shutter's tube. Stopping down makes the lens' exit pupil smaller, increases the angle from the edge of the exit pupil to the rear of the tube. This is why I don't agree with you.

I also have a tiny 45/9 CZJ Goerz Dagor in barrel. This little gem has (choose one) too small outer elements or too narrow a tube. Either way, stopping it down makes the exit pupil smaller and increases the angle from the edge of the exit pupil to the rear of the barrel. Another reason not to agree with you.