RZ67 lenses and diffraction
I just received a very nice used RZ67 with the 110mm lens and so far I am very happy with the way the camera handles. 135 is just too small for nice 16x20s (even if I use a tripod and slow film) so I stepped up to 4x5 where 16x20s, even when shot at f32, are pretty darn sharp. My question is, at what point will diffraction negatively impact image quality in a 16x20 print? I know, I know, I know this is a very subjective question but I shoot primarily landscapes and I like a lot of depth of field. My next lens will probably be one of the 65mms. I don't mind carrying the weight of the RZ kit-it may be the same as my 4x5 kit but the film is less expensive to purchase and process and the whole process is quicker. However I am interested in image quality, hence the question about diffraction.
Personally I wouldn't worry about it. The best way to know is for you to run tests to see what meets your standards. After running tests, and you like everything, then diffraction isn't an issue. But if you see a point where image quality declines, then remember to not go there.
Remember, the sweet spot of the lens is usually never stopped all the way down to the minimum aperture. The aperture halfway between the max and minimum apertures will give the best results. Knowing that, I'd shoot a scene at minimum aperture, and the same scene at the lens' mid-point on the aperture scale. Then compare.
Not exactly equivalent, but I've been using a Fuji GW690 with the 90mm lens to shoot landscapes etc. which I scan and print at 11x17. I don't have any problem with shooting at f/22 or 32 at this print size. Obviously you would be enlarging a smaller piece of film to a bit larger size, but I wouldn't be surprised if you find the results quite acceptable. Give it a shot.
Walt is dead right.
You can estimate the effect of aperture on diffraction by dividing the value 1760
by the f/stop, to see the theoretical limit of resolution with a perfect lens.
1760 / f5.6 = 314
1760 / f16 = 110
1760 / f32 = 55
The Resolution of a System can be estimated by adding the reciprocals of each element's resolution.
1/ Film Resolution + 1/ Lens Resolution + 1/ Enlarger Resolution = 1/System Resolution
100 line pairs per mm is a wonderful dream we all have, so plug 100 into each element of the system, and get a shock: 1/100 + 1/100 + 1/100 = 3/100 = 33.
With a perfect system, we can't image more than 33 lp/mm.
And, obviously, plugging in a single massively higher value, doesn't have much effect.
So, watch for the photographic potholes: shooting stopped down too far is a big one.
Camera movement is another. Focus error is a biggie, and so is the whole enlarger / scanner thing.
Depth of field turns out to be the inverse of resolution, so don't stop down too far.
And don't WORRY about the numbers, test, look at your prints, and see what works for you.
Edward Weston stopped down all the way, and then some, but his VISION was sharp and we STILL think it was his lenses. If you don't compose a picture using adjacent tones, it will have the illusion of sharpness, which is more important than actual sharpness.
for extra credit, build a microscope and discover the rayleigh criterion
apply it to photography, and promptly forget it
Last edited by df cardwell; 06-21-2008 at 08:53 AM. Click to view previous post history.
"One of the painful things about our time is that those who feel certainty are stupid,
and those with any imagination and understanding are filled with doubt and indecision"
I'd start at the other end. How much DOF do you gain going past F/16?
Originally Posted by scott k
For me I'd try to stay at F/11 or below most of the time.
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Originally Posted by df cardwell
I don't want to hijack the thread but I would like to read more about this thought, here, a PM or another thread.
I was out of town for the weekend, thanks for all the input.