apo lens for print color

[danzyc]

hello friend i made color print with a simple rodagon 80/4 and componon 50 2,8....i should switch with apo lens???? there s so necessary???

thanks

 

[2F/2F]

Not at all. I am sure that not one of my favorite pictures was printed with a nice, modern, expensive "APO" enlarging lens.

 

[PHOTOTONE]

In over 30 years of having my own commercial darkroom, I have always been satisfied with Componon and Rodagon lenses.

 

[keithwms]

Depends on the amount of enlargement.

 

[Q.G.]

If apo, than not just for colour, but for B&W too.

 

[nworth]

APO became a marketing catch phrase a couple of years ago. Most of the so-called APO lenses are not traditional apochromats, and I'm not sure all of them are even corrected at three or more wavelengths (which is more or less the definition of apochromtic). Many of the APO lenses are excellent performers, but there are many fine traditional enlarging lenses out there that will compete quite well with them.

 

[bob100684]

APO became a marketing catch phrase a couple of years ago. Most of the so-called APO lenses are not traditional apochromats, and I'm not sure all of them are even corrected at three or more wavelengths (which is more or less the definition of apochromtic). Many of the APO lenses are excellent performers, but there are many fine traditional enlarging lenses out there that will compete quite well with them.

I feel like this APO term gets thrown around a lot regarding camera lenses....anyone care to explain what it actually means?

 

[keithwms]

apo=apochromatic

All glass has an index of refraction n that varies some with wavelength (colour). Glass for which n is especially variable across the wavelengths is said to be especially dispersive.... it disperses the colours, like a prism. Glass that has a more constant n across the wavelengths is usually termed extra low dispersion (ED) or ultra low dispersion (ULD)... it tends to focus colours more equally. Elements made of such glass are now commonly found in many camera lenses to minimize the overall dispersion of the lens, which of course has many elements.

Apo lenses take the goal of ED/ULD elements a step further: they are designed to correct for dispersion through multiple elements so that the lens focus to equal distances across many wavelengths or, optimally, a wide range of wavelengths.

It is important to know that no lens is 100% apochromatic... it is a matter of degree and over a particular range of wavelengths. So indeed the term can be somewhat misleading. Nevertheless, I have some apo lenses that allow me to focus from the UV into the IR without correcting the focus (which is of course done with visible light). That impresses me greatly and saves me a lot of hassle when doing UV and IR photography. It means that I don't have to stop down like nuts to avoid misfocus.

"Apo" is more important with digital because most digital sensors have the "Bayer" architecture, in which the r,g, and b photosites are not stacked. Rather, they are laterally displaced (an important exception is the "foveon" architecture which remains very expensive to produce). Hence any chromatic aberration can be especially problematic, leading to loss of sharpness and contrast and colour fringes, especially about contrasty objects. So lenses with more low dispersion elements or true apo correction are ever more desirable. Notice that colour film has stacked layers of different wavelength sensitivity, so chromatic aberration is less an issue than with Bayer digital. But still, ED/ULD/apo lenses can be beneficial in film photography as well.

In printmaking, apo is sometimes considered important because papers can be sensitive into the near UV, so it's important that there not be a difference between the visible focus seen by the print-maker and the focus at bluer wavelengths. N.b this does not mean that an apo enlarging lens is necessarily apochromatic into the red or IR. Sometimes they are, sometimes they aren't.

 

[Thomas Wilson]

Bob, in a nut shell, an APO lens is corrected for chromatic aberration. These lens designs use more costly specialty glass and coatings so that the three wavelengths (RGB) of light are brought into focus on the same plane. This can reduce color fringing in areas of high contrast.

Danzyc, I have to agree with all of the previous responses to your question. Keep in mind that your final print is only as good as your weakest link in the process. For example, if your negative or transparency happens to have some color fringing on the high-contrast edges, the finest APO enlarging lens can not correct this, it will merely reproduce it accurately.

I would stick with a good 6 element lens, a properly aligned enlarger, glass negative carrier, and careful darkroom technique. Of course, all of this will be for naught if you leave the tripod and cable release at home when shooting.

Focus (I couldn't resist) on technique rather than a silver bullet.

 

[Q.G.]

Apo lenses take the goal of ED/ULD elements a step further: they are designed to correct for dispersion through multiple elements so that the lens focus to equal distances across many wavelengths or, optimally, a wide range of wavelengths.

Usually only three.
The idea is that when you choose a couple (achromat) or three wavelengths (apochromat) in different parts of the spectrum, and correct the lens for those, the in between colours will get closer to correction too.
And it works.

It is important to know that no lens is 100% apochromatic... it is a matter of degree and over a particular range of wavelengths.

Well, no.
It is not that difficult to correct for three wavelengths, and many lenses are indeed 100% apochromatic.
But remember that being an apochromat does not mean that all chromatic aberration has been removed.

A few lenses however are so well corrected that the effect of the remaining chromatic aberrations is below the effect of diffraction, so that the chromatic aberration has no limiting effect on image quality at all.
Zeiss (maker of the first one of these) calls these "superachromat". Pentax uses the term "ultrachromat" (i believe).

"Apo" is more important with digital because most digital sensors have the "Bayer" architecture, in which the r,g, and b photosites are not stacked. Rather, they are laterally displaced (an important exception is the "foveon" architecture which remains very expensive to produce). Hence any chromatic aberration can be especially problematic, leading to loss of sharpness and contrast and colour fringes, especially about contrasty objects.

The effect will be the same on film.

In printmaking, the need for correction is limited to the spectrum paper is sensitive too. But that is still wide enough for apochromats to make sense.

And it's not just good to avoid focus errors, but also to get sharper pictures with more accutance.


Having said all that, the terms "achromat" (most lenses are that) and "apochromat" themselves, when truly applicable, are not all deciding. They say very little about how the wavelengths in between the corrected ones behave.
So good achromats could be as good as, or even better, than lenses that 'technically' deserve to be called apochromats.

 

[keithwms]

It is not that difficult to correct for three wavelengths, and many lenses are indeed 100% apochromatic.

That is false. As a professional spectroscopist I know otherwise. No such thing as a 100% apo lens, period. Indeed, there are plenty of lenses that come very close, and for almost all practical purposes they suffice. But there is always a finite set of wavelengths across that are fed into the lens design and used for testing.

Correcting for only three wavelengths does not mean that the lens is 100% apo. The term apo is used a bit too loosely in commercial photography.

 

[keithwms]

P.S. QG, if we're going to have an extended discussion / debate on the technicals and the merits of colour accuracy and apo and all that then let me suggest splitting that discussion off to the new colour forum. It might be too far afield for this thread and it might confuse the issues brought up by the original post. See you in the colour group!

 

[Q.G.]

That is false. As a professional spectroscopist I know otherwise. No such thing as a 100% apo lens, period. Indeed, there are plenty of lenses that come very close, and for almost all practical purposes they suffice. But there is always a finite set of wavelengths across that are fed into the lens design and used for testing.

Correcting for only three wavelengths does not mean that the lens is 100% apo. The term apo is used a bit too loosely in commercial photography.

Keith,

Yes, the term is used quite loosely. Mostly to suggest quality, even where it is lacking.

The term "apo" meaning corrected for three wavelengths however is a traditional, 'strict' one.

And there are indeed lenses that are just that.


Where is that colour group?

 

[keithwms]

Yep, I am aware that the common photographic usage of the term is different from my more specialized usage. But I have my own good reasons for being picky about this, and it's an issue that is becoming more important, not less. Not the least of which, as you know, when people make prints on silver gelatin paper, they are dosing the paper with a fair amount of invisible light, for example...

http://www.ilfordphoto.com/Webfiles/20061302013402375.pdf

Where is that colour group?

QG, go to the menu bar beneath the APUG logo, it is right next to "Forums." Click on the CMY logo once you're in the groups page, and then you'll see the group discussion topics. Here's the tricky bit: you have to scroll down and look for the little bitty text that says "Join Group." Then you're in and we can talk smack in full colour

 

[Q.G.]

Thanks Keith.
But could it be that it is a subscribers-only thing? Because i can't see it.

 

[keithwms]

Oh I don't know. Guess so, if you don't see it. Well, subscribe then