I agree with your conclusions regarding grain.
Ideally, we want a lens that performs best at between f4-f8. We should be able to find that. Reversed enlarging lenses often perform best at 4-5:1, which is more magnification than we want.
Okay, I just bit the bullet at KEH, and bought an 55/3.5 Micro Nikkor (I got the Ai version, though I know the previous version has some interesting qualities, because it needs to work on my wife's D300), the correct Ai extenstion tube (Pk13), and also an old pre-Ai M tube. Oh, and a reversing ring. So, if I have to keep my magnification greater than 1:1, I can reverse the lens and add the additional ring. These lenses have always attracted magical reverence--I hope this one lives up to it. $133 total for all of the above--still a fraction of the price of that Computar.
Rick "who probably should get another Nikkor adapter for the Canon" Denney
That's a newer lens than mine. It should be a very good performer.
Make sure to check the various adapters for shiny surfaces, and it might help to make a baffle out of flocking material to put inside the extension tubes. If you need a small bit of flocking, let me know the size, and I'll send you a small bit. A diy lenshade with an opening only a little bigger than the image area would also help.
The Micro-Nikkor is a good addition to my tiny collection of classic Nikkors, bought for their classic status and excellent current price. I have the 105/2.5 and the lovely 180/2.8ED. And the Nikon Series E 70-150, which is an amazing lens for being a cheapie, even though I don't do much with it. I've wanted the Micro since about 1975 when a buddy of mine bought one and I saw the pictures he made with it.
Rick "looking forward to trying it out on this project" Denney
My initial test was at 1:1 with the extender. F/8 was again the sharpest aperture. F/3.5 showed obvious softening at the edges, and even f/8 didn't fully correct that. I was surprised, to say the least. But I can only assume that the field is not quite as flat at 1:1 as it is at 1:10, which is probably where this lens was really optimized.
At 1:1, the Canon 50/2.5 Compact Macro and Life-Size Converter out-performed it. The center was the same, but the edges were very much better with the Canon. Again, I was surprised. I'm not sure I should have been, though, since I'm not usually subject to the Nikon Kool-Aid. The old Micro-Nikkor is a double-gauss design with five fixed elements, and the Canon lens is a 7-element double-gauss design with two additional corrector elements that are fully floating. And the life-size converter is not an extension tube but a specially designed 4-element optical converter specially made for this lens. As Kingslake would say, it has many more degrees of freedom in the design. But the Nikkor is still better in terms of falloff where the Canon lens does poorly, which is a limitation in this application.
But one cannot reverse the Canon or add extension tubes--Canon would rather you buy their specialty macro lens for greater than 1:1. Given that I'd gotten better results with a cheapie 80mm normal lens reversed on bellows, I took the Nikkor and reversed it on the extender. Reversing it moves the glass much further away, so with the extender, the magnification was about 1.5:1--not quite as much as I'd gotten with the reversed 80mm lens. It has about the same field of view as a APS-C (DX in Nikon-speak) sensor at 1:1. An important advantage to being used this way is that I get more magnification than I can get with the Canon, but still in a lens fast enough to provide an autofocus confirmation (with my electronics-equipped adapter). I found the focus confirmation to be dead-on accurate at f/3.5, and then I stopped down manually. Reversed at 1.5:1, and at f/8, the Micro-Nikkor was completely sharp to the corners and rendered grain, though a touch more softly than the reversed 80mm lens. But I was still able to sharpen radically at a sub-pixel radius and still get quite smooth images at viewable sizes. This will be my working setup, I think. It's not really any sharper than the reversed 80mm lens on bellows, but the provision of a working focus confirmation tips the scales.
The reversed Micro-Nikkor has another really nice feature. The rear of the lens has a rectangular opening as a mask for the lens when it's racked out in normal use. I can use the focuser to extend the rear of the lens out as far as I like when reversed. It makes a very efficient shade that can be nailed right down to the edges of the field of view. That's a good thing in this application.
Rick "who now thinks the 5D AA filter is the limiting factor at 1:1" Denney
I took my samples for the lighthouse picture with the Nikkor reversed at 1:1 magnification, confirmed by photographing a mm scale. (I used an extension ring too, I can't remember which one.) I used F5.6. The big difference is that my camera has a DX sensor.
The smaller sensor makes a big difference in a lot of ways. I now also know how you got such even illumination, heh.
In the center, there was no observable difference between f/5.6 and f/8. But the difference in the corners was definitely observable.
Just to be goofy, I'd like to try my P67 135mm Macro-Takumar. It's a dialyte design, apparently pretty symmetrical. But I don't have a way to mount it just yet, and whatever I use has to be strong--that's a big, heavy lens. I had it out today and pondered it--I need it this weekend for another project. I'd probably spend my time better by mounting that Magnagon, heh.
Rick "doing some art copy work this weekend, on digital and on film" Denney
Yep, the tube was a short one, one of Nikon's old 'K' sets.
One key to even illumination is to make the light source significantly bigger than the negative. I found that out when doing some masking on my Cezanne.
I'm thinking that 1:1.5 would be just about perfect, though, for digitizing old 35mm color slides on a DX camera like my wife's D300.
Rick "who can get to about 2.5:1 with this rig" Denney