What does APO mean?

<p>Hi All, I'm new to LF and having a lot of fun doing it. I was just wondering what APO on the lens' means?</p>

<p>Apochromatic. All wavelengths of (visible) light focus at the same point. Wikipedia has a decent explanation. http://en.wikipedia.org/wiki/Apochromat</p>

<p>thanks, Greatly appreciate</p>

<p>As Franklin says. Keep in mind that it applies to B&W as well. What it all amounts to is that apo lenses are sharper, in practice, for color or B&W.</p>

<p>There are several definitions. The longest standing one is that three colors be brought to the same focus. This was a critical requirement in some applicaitons, such as three (primary) color separations in graphic arts / printing, when this was done by lens & film photographic techniques. Currently the German LF manufacturers cite some DIN standard, which apparently requires high color correction, but isn't so specific about three colors. It may also be a tradename arms race -- once one lens manufacturer starts using "apo" in their lens names, if another doesn't, they might lose sales. </p>

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<p >I agree with Michael and the the color correction is achieved with coating of the lens in order to bring the three colors to the same plan. First the lenses were single coated than full coating and even multi coating appeared. But there is rumors that uncoated lenses works much better on black and white film as the images have more crisp. The evidence is the uncoated pre war Goerz lenses. Also we did tests with uncoated and coated lenses on slide and the result were that we could hardly see any differences.</p>

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<p >The name of Apo come up in the process industry and the case could be as Michael wrote:</p>

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<p >“It may also be a tradename arms race -- once one lens manufacturer starts using "apo" in their lens names, if another doesn't, they might lose sales.¨”</p>

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<p >The only significant difference I can see between those is when using Apo-lanthar in general photography. That's probably explain the high prices of the lens. Nowadays I don't use any colors because of the instability of the material.</p>

<p>The importance of the "three colors" all focusing at the same plane is also because they're talking about the primary colors. It works out that if all three primaries focus well, then the rest of the colors will focus closer to the same plane as well.</p>

<p>Back in the day, non-apochromatic lenses were likely to be very well corrected for two primaries, and this was considered acceptable for general photography. I'm not absolutely sure, but this is probably still true today -- except that the non-apo lenses these days would seem to be much closer in performance to apo lenses than those of the past, generally speaking.</p>

<p>I believe that, from what I've read over the years, the design factors for an "apo" lens are such that this is taken care of in the lens formula, part of which involves choosing the different types of glass that go into the production of the lens -- apo lenses have more complicated designs using more exotic and expenses glasses than non-apo lenses, and the quality control must be much tighter, thus the higher cost.</p>

<p>This is why an uncoated lens can be apochromatic. Coatings improve contrast and reduce flare to a certain extent, but have little to do with actual focus.</p>

<p>Sorry, for my mistake not to mention the glass and of course it has much importance too and Mr Hendrickson is right about it. But, I believe that coating or multi coating works hand by hand with the glass. Wich type of glass were used, a less flare, and the higher contrast because of coating and their cobination gives you a quality like of Apo Lanthar.</p>

<p>The Apo designation for large format taking lenses and photographic enlarging lenses is "that the lateral chromatic aberrations of the secondary spectrum have been correct to within a very small percentage of the focal length".<br>

The Apo designation for lenses used for microscophy is the traditional Abbe definition where "the primary color rays cross at a common point". This is also the common definition.</p>

<p>Here is the sample of a Dogmar convertible which I'm selling because I don't have a format to the lens. This is an uncoated lens but color corrected with out the name of Apo. Read it.</p><div></div>

<p>APO can have two meanings. As created for photomechanical reproduction, they are designed as "peaked apochromatic" correction. That is, full color correction at the 25 or 29 red, the 58 green, and the 47 blue. in between those positions, they may not be accurate but it doesn't matter for color separation. Obviously, the quality of color films will be very good with these lenses but they could be better with "balanced apochromatic" correction.<br>

Most of the modern 6 element APO's have "balanced apochromatic" correction. The color correction is a nearly straight line regarding performance, not just at filter positions. The performance of these lenses for use with film is superior. </p>

<p>All apochromatic lenses are apochromatic at one magnification only! That doesn't mean that different magnifications are poor, for they are nearly all excellent in quality. It just means that one color is off a tiny bit and you can't see that unless you are a scientist.</p>

<p>Color correction can be either "on axis" or "off axis". On axis is easier to achieve it merely means that R, G, and B images focus on the sme plane. Off axis or lateral color may have a problem in which while the RGB are focused in the same plane, one or more of them may be physically larger, showing color fringing (and in b/w, fringing may be seen also). Stopping down will help on axis failures but off axis failures actually intensify the problem, making the fringing sharper. Coma and Astigmatism must be corrected to a high degree and in a few cases Oblique Spherical aberration is reduced for better contrast and finer detail.</p>

<p>The four element all air spaced (Artar) type designs are all "peaked correction" and have narrow fields of view, somewhere between 35 and 45 degrees. </p>

<p>The 6 element plasmat type designs are mostly "balanced correction" and cover from 70 to 80 degrees.</p>

<p>Lynn<br>

</p>

<p>Hello gentlemen!<br>

The problem for us - the end users - is that there is no clear-cut definition to an "APO". The problem with lenses (incl. photographic lenses) is that they can not focus light of different wavelenghts at the same point. Neither can an "APO". The problem is red light in particular wich is why using an APO for enlarging B&W is not as important as during the shooting. Photographic paper is not red-sensitive.<br>

A lens called "APO" by company A may not be an "APO" with company B. Therefore, dont worry about the "APO" designation. It does not necessarily assure you a sharp lens!.... At least you dont know untill you have tested the lens, and a non-APO may be as good or even better!!.<br>

Regards, Per (owner of three APO's!!). please forgive my lousy spelling ;-)</p>

 

<p>Per,</p>

<p>Schneider and Rodenstock use exactly the same definition of Apo for taking and enlarging. And an APO enlarging lens will perform better for B&W as well as color printing and shooting. Since an Apo lens means that color fringes are reduced or eliminated fine lines reproduce sharper with an Apo lens.</p>

<p>its means is 非球面 in chinese</p>

<p>Hello Bob<br>

How do you know that Schneider and Rodenstock use the same definition of APO, and what is that definition??.<br>

The APO corrects cromatic aberration and will therefore focus blue, green and red light better than a non-APO. However, the main problem is red light and as photographic paper is not red-sensitive it will not "see" the main problem with the non-APO. - I see no difference in performance with my present APO-Rodagons compared to my old non-APO rodagons. I probably would if i was doing color-printing. Only if the APO is superior in focusing blue and green light will it make a difference in B&W printing - Anyway that is my experience ;-)<br>

Regards, Per</p>

<p>Because we are the distributor for Rodenstock and linhof so we also sell Schneider and did the normal thing. We asked. Both have exactly the same definition as do other lens manufacturers and "The Phototonics Dictionary" which is a book of definitions for purchasing agents in the optical industry.</p>

<p>A lens in which the lateral chromatic aberrations of the secondary spectrum has been reduced to a small percentage of the focal length of the lens.<br>

As I stated above, this is the definition used for photographic lenses. For microscope optics the definition is the one from Abbe that the rays cross at a common point. This is also the definition used for some process lenses in multiple plate printing where all of the negatives had to be exactly the same size to line up properly for reproduction.</p>

<p>As for your enlarger, you are using the recommended glass negative carrier and have critically aligned your enlarger? Correct?</p>

<p>Hello again!<br>

Thanks for pointing me in the direction of a definition to the words "APO". Out of curiosity i will search for a copy of "The Photonics Dictionary" for a closer study ;-). I am still curious, what is "a small percentage of the focal length of the lens"? Is it the same percentage for all APO's?.If not, i still dont see how you can compare them.. Besides photography i am interested in astronomi and as far as i have learned there are HUGE differencies in the performance of apocromatic refractors!!.<br>

As for my enlarger; yes, i use glass for 4x5", but not for 35mm and 6x7cm. It is well aligned. My observations are based only on visual inspection of enlargements from 6x7cm and 4x5" negatives. I have never made any closer testing counting lines pr. mm.<br>

Regards, Per</p>

 

<p>Enlarging lenses are made to be used with a glass carrier for all film format sizes, including 35mm to 4x5". Use glass and the optimal aperture and you will get all of the quality that the lens is capable of.</p>

<p>And there is a significant difference in performance between an Apo Rodagon and the Apo Rodagon N series of lenses. Which do you have?</p>

<p>As for the percentage it varies by focal length but it is fairly consistent between lens manufacturers. </p>

<p>I have the APO-Rodagon, not the N-version, so that might explain my experience. I agree that using glass in your negative carrier will give you the best result and i have always used it for 4x5".<br>

I also agree that as long as all manufacturers use the same percentage for the same focal length you can compare lenses, but only if they use the same mathematical definition....<br>

Regards Per</p>

<p>"The Apo designation for large format taking lenses and photographic enlarging lenses is "that the lateral chromatic aberrations of the secondary spectrum have been correct to within a very small percentage of the focal length".<br />The Apo designation for lenses used for microscophy is the traditional Abbe definition where "the primary color rays cross at a common point". This is also the common definition."<br>

Bob:<br>

So, what would you call a photographic lens that meets the traditional Abbe definition? Such lenses really do exist: <a href="http://www.coastalopt.com/mmapomacro.html">http://www.coastalopt.com/mmapomacro.html</a> . <br>

The sad thing for S. and R. is that they've painted themselves into a corner by using a dumbed-down (and in my view completely bogus) revisionist definition of "apochromat". When Rodenstock finally sells a REAL apochromat what will they call it?<br>

BTW: I am a lens designer, optical engineer, and lens manufacturer.</p>

<p>Many were process lenses for making separation negatives (plates) for the graphic arts industry. We also used them in aerial reconnaissance for doing copy work in the USAF in the 60's. Don't know if they still do that on film today.</p>