150mm G-Claron Sharper than 180 Componon-S?

[Drew Wiley]

180 is a bit short for 5x7.

[Bernice Loui]

Durst 138:

5x7 neg, 240mm f9 APO Artar, 2x to 3.5x. Print exposure at f16 or f22

4x5 or 6x9 neg, 180mm f9 APO Nikkor, 2x to 5x. Print exposure at f22.

Appears shorter focal lengths are used when enlarger to base boards distance is not easily achievable. IMO, using the shortest possible focal length of enlarger lens is not a good trade-off, using the longest possible focal length for a given film size is preferred.


Bernice

[Pere Casals]

Amazing...in very carefully examining center and edge detail in a 20x30 print made with a 180mm Companon-S, and the same print as a 30x40 made with a 150mm G-Claron...the Claron wins! How is this possible? And the Claron, to boot, has an amount of dust in between elements which might be cause for some concern. Companon-S Stopped to f/16, Claron to f/22. Heiland LED VC light source. Go figure!

I'd say that by f/22 or f/16 those lenses are not in the best aperture for best resolving power. For the S it may be f/11. At f/22 you have pretty diffraction.

If you have better result at f/22 it may be because better DOF if alignment is not perfect.

To know it for sure I'd do next test:

Place a USAF 1951 glass slide (having Group 7) in the enlarger, tilt it to horizontal, place DX DSLR (like nikon D3300, with no lowpass optical filter) in a tripod without lens at the enlarging distance, projecting the slide on the sensor, use tethering to see it in a big PC monitor, focus until optimal, repeat with slide in the corner/center and from f/5.6 to f/16. See what group/element to measure Lp/mm.

You will know the quantitative lp/mm seen from the medium and, dividing by magnification, the amount you have in the print, if resulting 6 lp/mm or more in the projection then only an eagle would see a flaw.

There are a lot of things in an enlargement that would prevent an optimal result, and the less common it's the lens... IMHO.

To compare two enlarging lenses a lot of things have to be in perfect conditions.

[mdarnton]

This wouldn't reveal field curvature, would it? An important factor for printing.

[Pere Casals]

This wouldn't reveal field curvature, would it? An important factor for printing.

Yes, Michael, this is true, but it removes the aligment factor in a DIY lens evaluation. Anyway we can consider that enlarger lenses are very well optimized for field flatness.

If wanting to evaluate field curvature then we'll need a flat support in the back of the DSLR and placing it on the easel, it also can be done, not difficult, but we would need that DIY support. In that case it has to be a more accurate test, to not mix the enlarger alignment with the lens field curvature.

[Peter De Smidt]

Note also the work done by Roger at Lens Rental. See: https://www.lensrentals.com/blog/201...e-focus-point/ . The upshot is that it might not be best to focus in the middle of the image.

[jose angel]

Peter, for whatever the reason I cannot open your link. Anyway, I suspect it also refers to field curvature; when it becomes a problem, better to focus somewhere between the center and the corners, to get not the sharpest center score but a sharper overall image. Closing down the lens, image sharpness is improved thanks to DoF.

[Drew Wiley]

If your image plane, both neg carrier and easel, are truly parallel, along with the lens itself, f/22 will NOT give you a sharper print. Something is off.

[Pere Casals]

Note also the work done by Roger at Lens Rental. See: https://www.lensrentals.com/blog/201...e-focus-point/ . The upshot is that it might not be best to focus in the middle of the image.

This is a very interesting test.

Anyway shown examples are about taking lenses (cine).

While a complete flatness is not possible, with enlarging lenses flat field can be virtually considered thanks to special design, a drawback of those designs is limited coverage to around 50º in a lot of designs.

Of course performance may vary across the field and with magnification and aperture, but field flatness it's always very good in enlarging lenses, to the point that at practical apertures DOF ensures that any focus flaw comes from alignment or from film flatness, and not from field curvature.

[Pere Casals]

If your image plane, both neg carrier and easel, are truly parallel, along with the lens itself, f/22 will NOT give you a sharper print. Something is off.

IMHO a bit it depends on the magnification, at /22 limit is 71 Lp/mm at extintion, so at 10x scale you still have a 7.1Lp/mm limit on paper, also in the limit of the human vision, but having several factors in the limit it should have a comulative degradating effect.

By f/11 limit is 141 lp/mm, so I guess that for 10x (14.1 on paper) it has no diffraction degradation detectable by human vision.

From theory, I guess that at 5x and f//22 diffraction should not be seen on paper.