8x10 APO lenses, f-number < 4.5

[genotypewriter]

Not surprised... it's funny how there are proper APO lenses for high magnifications as well as for infinity (telescopes) but for nothing in between?

Wonder if the said Nikkor AM lenses perform just as well for low magnifications. The 210mm f/5.6's rated 155mm circle should be fine for 4x5" even at infinity.

[pdmoylan]

There is a European website (naturefotograf.com?) with LF lens evaluations who speaks of the 120mm f5.6AM lens as usable for smaller magnifications (on 6x9) with good results. I am not aware of any others who have used these lenses for other than their 1:1 purpose. In fact, I am not sure whether the 210mm AM has enough coverage for 8x10 if used at more normal magnifications 1:10 etc).

Since chromatic aberations can change subject to magnfication and aperture, I doubt one can draw a conclusion about whether an APO lens manufactured for a specific purpose will remain an APO at all magnification and apertures.

[Hermes07]

Not surprised... it's funny how there are proper APO lenses for high magnifications as well as for infinity (telescopes) but for nothing in between?

Wonder if the said Nikkor AM lenses perform just as well for low magnifications. The 210mm f/5.6's rated 155mm circle should be fine for 4x5" even at infinity.

Probably because it is impractical to make a lens apochromatic over a range of reproduction ratios, and because there are very few cases where lenses actually need to be strictly apochromatic. For general purpose photography work at a range of apertures and magnifications, there are bigger issues and bigger priorities. I'd imagine trying to reproduce half-tone dots against a white background or bright stars against a black sky would show up chromatic aberration that would be invisible in most scenarios.

[genotypewriter]

There is a European website (naturefotograf.com?) with LF lens evaluations who speaks of the 120mm f5.6AM lens as usable for smaller magnifications (on 6x9) with good results.

Thanks. Yes, I've come across this page before but forgot about it:
http://www.naturfotograf.com/lens_LF.html

In fact, I am not sure whether the 210mm AM has enough coverage for 8x10 if used at more normal magnifications 1:10 etc).

I've seen Nikon's rated image circle figure at 1:1 as 310mm at f/5.6 (400mm at f/22). So it'll only be good for 4x5 at infinity.

Since chromatic aberations can change subject to magnfication and aperture, I doubt one can draw a conclusion about whether an APO lens manufactured for a specific purpose will remain an APO at all magnification and apertures.

Ironically, the amount of CA visible and APO-ness can be two different things. APO strictly means the focus needs to bring three wavelengths to the same point like this:
http://en.wikipedia.org/wiki/File:Ap...ocal_curve.svg

But it doesn't have anything to do with how much variation (CA) will be there at other wavelengths in between.

So a proper APO lens remains APO at all magnifications but CA visible at the wavelengths its not optimised for will get magnified.

Probably because it is impractical to make a lens apochromatic over a range of reproduction ratios, and because there are very few cases where lenses actually need to be strictly apochromatic.

Yes, that would be difficult but I guess picking a middle magnification like 0.5 (instead of 1 or ∞) and making it APO for that should be possible.

For general purpose photography work at a range of apertures and magnifications, there are bigger issues and bigger priorities. I'd imagine trying to reproduce half-tone dots against a white background or bright stars against a black sky would show up chromatic aberration that would be invisible in most scenarios.

In my experience I've found stars are a good subject for evaluating coma more than CA. My favourite subjects for checking for CA are tree leaves against a white sky