8x10 APO lenses, f-number < 4.5

[genotypewriter]

Question for the experts: What are the fastest APO lenses made for 8x10? Are there any faster than the f/4.5 APO Lanthars?

Just wondering since most APO lenses are relatively slow.

[E. von Hoegh]

No. You have to settle on a definition for "apochromatic", too. The Apo-Lanthars had a relative apochromatic correction and a wide aperture, they do not compare well with the graphic arts apochromats, which were corrected to focus the three primary colors on the same plane, at the same size.

You can't have your cake and eat it too. The money spent on a 300mm Apo-Lanthar would buy a few Artars in shutter. Maybe even a modern Apo Symmar, which has a better correction and a wider field than the Lanthar, comes in a modern shutter, and so on.

[genotypewriter]

Thanks for that reply.

So when you say "relative apochromatic correction" do you mean to say that they technically don't bring three wavelengths to the same plane but still have a very low total delta value so that CA is greatly minimised?

Some of the 35mm format APO Lanthars don't seem particularly APO-like (e.g. 90mm APO Lanthar) but others are excellent (e.g. 125mm f/2.5 APO Lanthar). Wondering if this explains it.

Thanks again.

[Dan Fromm]

Geno, the DIN standard that Schneider and Rodenstock appeal to when they claim that their modern taking lenses are apochromats is mentioned here: http://www.schneideroptics.com/info/vintage_lens_data/large_format_lenses/apo-artar/apo_artar.pdf

In this http://www.largeformatphotography.info/forum/archive/index.php/t-47957.html discussion on this board, Emmanuel Bigler explains it at some length, also sticks pins in marketing claims based on it. He sticks more pins in them here http://www.galerie-photo.info/forumgp/read.php?2,2952,3275#msg-3275 If you don't read French, Google Translate will help you a little; in my experience with it, it hasn't lived up to Google's claims.

Short version, the Norm seems to have been withdrawn. The term as used by marketers has minimal implications for lens performance. Bob Salomon, who is almost always a powerful force for good, will probably chastise me for casting aspersions on Schneider's and (horrors!) Rodenstock's marketers. I don't mean to suggest that the two firms' recent large format offerings are anything less than extremely good.

On the whole, crapochromatic may be a good and useful word.

[Oren Grad]

Not to mention that the 35mm-format Apo-Lanthars have nothing to do with the large format Apo-Lanthars. Another marketing thing - Cosina bought the rights to the old Voigtlander names and has been deploying them freely. They're quite good lenses, mind you - but no relationship the old ones optically.

[pdmoylan]

Me thinks that Messrs Bigler and Fromm have mistaken MTFs for the degree of alignment of various colors upon the surface of film. Many achromats assure a high degree of resolution and hence MTF measures. It is my understanding from knowledgable sources that one needs to consider Schneider's transmittance curvesm for example, for a more complete insight into this question. It is the elimination of color fringing caused by primarily chromatic aberation, not the degree to which a lens construction has eliminated falloff, distortion etc, that is at issue.

It seems to me in poor taste to express an opinion in this area unless one has the ability to test each lens for its degree of freedom from chromatic aberation and quantify their findings. APO being relative, I think we can fairly assume that newer apo lenses probably improve the alignment of colors and hence the reduction of fringing.

The MTFs of Sironar Ns, Ss, Ws, or their APO successors to me do not provide any evidence of their color correction. Surely improved designs, glass types, and more exacting manufacturing tolerances via state of the art manufacturing processes likely provide more consistent results, improved contrast and possibly resolution. I have yet to see any tests which have identified the relative color fringing issues with LF lenses.

[genotypewriter]

Thanks for the inputs everyone. Some very nice info there, Dan.

So I guess this means the APO designation doesn't mean much. Ok... what lenses are truly apochromatic, whether APO is written on the box or not? I'm guessing there are ways to tell/guess by looking at the design?

Which brings me to another question... if we take a the fundamental design of a proper apochromat and then make one with very low dispersion glass and another with relatively high dispersion glass (while sticking to similar refractive indices), what differences can we expect to see? My intuitive guess is that the focus in both will still be a polynomial function of wavelength that becomes 0 at 3 places but the high dispersion version will have a larger range of focus(-error)?

[Dan Fromm]

Ok... what lenses are truly apochromatic, whether APO is written on the box or not? I'm guessing there are ways to tell/guess by looking at the design?

Two questions that demand at least three unsatisfying answers.

You want a list of apochromats? Some makers claim that some of their process lenses are apochromats and prefix their names with "Apo-". Some of these lenses may be apochromats. Other makers of process lenses don't make the claim. Some of their process lenses may be apochromats anyway. When in doubt, ask the lens.

Tell at a glance? Not safe. Some tessar types, some dialyte types, and some heliar types are claimed to be apochromats. Others aren't. Nikon doesn't claim that Process Nikkors are apochromats, does make the claim for Apo-Nikkors. There are also 6/4 double gauss and plasmat type and 6/2 dagor type process lenses that are claimed to be apochromats. Such claims aren't made for other lenses of those types. When in doubt, ask the lens.

The only rule of thumb that has a chance of working is that slow process lenses are more likely to be apochromats than faster lenses sold for other purposes. When in doubt, ask the lens.

Another rule of thumb that does work is that for black/white work chromatic aberration's effects can be eliminated by using monochromatic light. Many aerial camera lenses are poorly achromatized, must be used with heavy filtration.

[genotypewriter]

When in doubt, ask the lens.

I should've thought of that earlier :) So then does anyone else know of lenses that are definitely apochromatic?



Another rule of thumb that does work is that for black/white work chromatic aberration's effects can be eliminated by using monochromatic light.

Yes and this is a solution for those who want to minimise CA-induced softness. Just to clarify, I'm curious to know about lenses that are truly apochromatic, after the getting to know from here that the apo designation doesn't mean much.


[QUOTE=Dan Fromm;876390]Many aerial camera lenses are poorly achromatized, must be used with heavy filtration.

Thankfully, mine aren't. Well except for the Aero Ektar that has some serious yellowing and needs a filter just to balance the colours.

[pdmoylan]

BTW, to the best of my knowledge, the only lenses which are purported to be free of longitudinal chromatic aberations are the Nikkor AM lenses, but only at 1:1.

[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:Apochromatic_focal_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 :)