has anyone ever made a 1:1 projection print (basically, contact print size but with an enlarger)?
I've always had it in the back of my mind to do this. to try to make 2 identical prints, one by contact and one by projection, to see what the subjective differences are.
The contact print would be (slightly) sharper and contrastier, because the image will not have passed through a lens. Can't argue with the laws of physics.
Paul -
Yes, several years ago I tried comparing a 4x5 contact print with a 4x5 projection print of the same negative. The projection print was pretty good, but it was easy to tell them apart. However, the projection print had to be suboptimal for at least two reasons - first, I didn't have on hand an enlarging lens optimized for 1:1 - I was just using a garden-variety EL-Nikkor computed for the usual range of 2x enlargement and beyond. Second, the grain focusers I have on hand don't do well near life-size, and I'm not sure focus was optimal, though it had to have been pretty close. In this experiment as in so many others, it's not easy to hone one's technique to the point where one can be confident that the results are limited by the tools and materials rather than slop on the part of the user.
"The contact print would be (slightly) sharper and contrastier, because the image will not have passed through a lens. Can't argue with the laws of physics"
I'd bet the contact print would be sharper too. but i'm also interested other qualities, like rendering of tones.
And I wouldn't assume that the laws of physics as we understand them would predict anything with certainty in cases like this. Observed reality is often more complicated and interesting than predictions based on simple laws.
For example, in the contact print case, there's the issue of a difused light source, and light scattering in different ways than it does with the projection print, which is capable of focusing on the actual emulsion layer. I doubt this (or similar effects) would actually make the projection print sharper, but they're examples of the kinds of complications that can make results interesting.
And yeah, I think you'd want to use a 1:1 process lens like a g-claron (which I don't have) to get the best results.
Paul, thanks for the suggestion on 1:1 printing, I went back into the darkroom this morning to try your idea. By the way, it's easier to adjust a bellows extension for 1:1 and then adjust focus by moving the head. I focused on paper and could easily view 40 lp/mm in the grain magnifier. The print was made on contrast 4 and was carefully printed for equal line/space pairs. The print has a resolution of 12-14 lp/mm.
With the same focus setting, I printed a negative that I had a very good contact print of, wrt contrast, tones. The subject was El Capitan in Yosemite, basically a rock wall. What was striking was, at a reading distance of 10"-12", the noticeably sharper contact print. The contact print was more pleasing, jumped out at you. The "enlarged" print was lacking life when compared side-to-side with the contact.
On studing the contact print, it was the local "contrast" that made me feel it was sharper. High acutance made the details just "pop".
Has anyone ever used an unsharp mask for printing? I understand it helps for edge sharpness.
Many thanks indeed to Patrick T. to share his experiments with us. I like very much the idea of a fair competition between a contact print from a 4"x5" neg and a 1:1 "enlarged" print from the same neg.
And let's try to argue "with" or "against" the laws of physics (I hope that Mark S. will
allow me to argue ;-);-)
First, I agree with Paul R. that even a good 6-element enlarging lens is usually designed for a magnification ratio between 2x and 10X, sometimes up to 20X for the APO series, but definitely not for 1:1. Special 1:1 enlarging lenses exist as well as the good ol' process lenses (apo-ronar, etc..) but I'm not sure that the issue is actually here. Anyway, let us stop down the enlarging lens to an "engraved" f/16 which is actually an effective f/32 at 1:1 ratio as far as diffraction (and photometric) effects are concerned.
Assume that stopped down this way the lens is pretty close to being diffraction-limited ; a conservative evaluation of the cut-off period @ zero contrast is 32 microns ; actually a really diffraction-limited lens @ f/32 can provide some contrast up to about 22 cycles per mm if we consider 0.7 micron as a reference wavelength (again, this is conservative since B&W paper is sensitive to 0.4 / 0.5 micron wavelengths). So let's assume, based on the laws of physics, that we resolve up to 30 microns for a visible period, this is about 30 cycles per mm, again a factor about 4 above the reasonable visual limit of 7 cycles per mm for a print seen from 10" (250mm).
So there is something that does not work
- either the lens is actually 2x to 4x worse than the theoretical diffraction limit, which I do not believe at all @f/16 (N_eff : effective f/32 @1:1 ratio),
- or the sharpness criterion based on the ultimate visible cycle @ zero contrast due to diffraction equal to (N_eff x lambda) is irrelevant to the evaluation of the visual quality in a good paper print.
My feeling is that the 2nd idea is closer to reality than the 1st, i.e., for sure, it is good to check what is the actual resolution limit for the image of small periodic objects like the USAF test chart, but this is not a sufficient criterion for a reasonable assessment of a good print.
Since we like to refer to the laws of physics, it is interesting to mention here what the laws of physics say as far as the resolution limit of a contact print are. Basically there are two limiting factors :
- a geometrical blurring effect (the simple geometrical shadow-cast effect)
- a Fresnel diffraction effect.
The geometrical effect is simply the fact that if the light source is seen under an angle "theta" from the contact printer and if there is a small gap "g" between the paper and the negative you should expect a resolution limit due to a simple shadow-cast effect
r_geom ~= (theta x g).
So a diffuse light source (theta = big) for contact printing yields a certain lack of sharpness w/respect to a point source (theta = small), for the same value of the air gap "g".
The Fresnel diffraction effect, in the unrealistic limit of a perfectly collimated beam (theta = 0) yields another blurring effect r_diff which is about the square root of lambda x g i.e.
r_diff ~= (lambda x g )^(1/2)
where lambda is the wavelength of light.
Assume that we need a resolution criterion of 30 microns, consider a light source of about 1 radian wide (~60 degrees) we are allowed an air-gap of 30 microns. In a traditional contact printing frame we are probably better than that, I have no idea. As far as the Fresnel diffraction effect is concerned, take a very pessimistic value of 1 micron for the wavalength lambda, we are allowed an air-gap of 900 microns ((900)^(1/2) = 30) i.e. about 1 millimetre in order to reach a 30 microns resolution limit ! so it is clear that in a contact print, diffraction is absolutely negligible whereas in an enlarging lens used to its optimum f-stop, diffraction is definitely non-negligible since at the best f-stop aberrations and diffraction contribute half and half.
At the first glance, the conclusion could be simple : want nice sharp prints ? no problem, use a large format camera an contact-print !! Achieving 40 cycles per mm, i.e. a limit cycle of 25 microns sounds reasonable with a modern lens covering 8"x10" and modern film. Achieving the same with an enlarging lens is certainly more difficult.
There is another very difficult issue which is the comparison of noise between and enlarged negative and a contact print. The noise you see on an enlarged print with a focusing loupe device is not simply the geometrically enlarged pattern of film grains, the statistics of density fluctuations is heaviliy modified when passing throught a lens. And this "noise transfer effect" is certainly different in a contact print.
a small corection to the above figures : the theoretical limit period @zero contrast for an effective F/32, diffraction-limited lens @ 0.7 microns wavelength is : 32 x 0.7 = 22 microns, i.e. about 45 cycles per mm (1000/22). This does not change the conclusions i.e. that it is extremely dificult to achieve this resolution in an enlarged print.
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