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What exactly am I going to get with the Nikkor AM*ED Macro lenses that the standard lenses of equivalent focal length don't provide? And, equally important, what am I going to give up by using them in standard landscape applications, often focused at infinity?
The lenses are of symmetrical construction. By a simple optical argument, they are optimized for 1:1. This symmetry argument doesn't tell how much worse the perfomance at infinity is: extremely slightly, or greatly worse.
Compared to the more common and less expensive plasmat designs (e.g., the Nikkor-W, Symmars, Sironars), the AM-EDs have less coverage. The diameter of coverage that Nikon cites is for 1:1 -- they aren't always clear about this. Nikon's figure for the 120 mm AM-ED is 55 degrees, 210 mm diameter. From the 55 degrees, it is clear that the 210 mm diameter is for 1:1. At infinity, the diameter would be approximately 105 mm, which won't cover 4x5. Most plasmats cover 70 degrees or more, which would be 168 mm diameter for a 120 mm lens at infinity. So if you want to use the lens at infinity, (and you believe Nikon's coverage figures), you are giving up a lot of coverage compared to less costly lenses.
Bjørn Rørslett reports that the 120 AM-ED works well for "general purpose photography" for 6x9 cm: http://www.naturfotograf.com/index2.html
The 210 mm AM-ED is listed as covering 51 degreees at f22: 400 mm at 1:1 or about 200 mm diameter at infinity.
Hmm. Plasmat types asymmetrical? Hmm.
Hmm again. AM-ED Nikkors not plasmats too? Hmm.
Hmm, macro lens. Designed for close up work. Usually used to record two dimensional things to film.
Hmm, landscape photography shot at infinity.
I ain't an optical engineer, but common sense says don't use a screw driver as a hammer, so why use a macro lens to do landscapes?
My half-penny observation.
Dan, I compared the Apo-Macro Nikkors to "more common and less expensive plasmat designs", not to the generic plasmat design, and I listed some by name. To be more specific: I was comparing to plasmats such as the Nikkor-W, Fuji-W, Fuji-CMW, Symmar-S, Apo-Symmar, Apo-Symmar-L, Apo-Sironar-N, Apo-Sironar-S.
You have to go back many years for general purpose plasmats to be symmetrical. The design concept is symmetrical, and is then tweaked to be almost symmetrical to better image the non-symmetrical case of distant objects. All of the modern general purpose plasmats are not perfectly symmetrical: their manufacturers tell us that they are optimized for distances and usually one can tell that the front and back elements are different from the cross section diagrams. Even the cross-section diagram of the plain (aka convertible) Symmar in a brochure (probably a datecode of 1970) I have is plainly not perfectly symmetrical. In contrast, Nikon describes the AM-ED lenses as having "completely symmetrical lens construction" and "are designed exclusively for macro photography and provide outstanding performance at 1:1 reproduction".
There are some symmetrical plasmats that do well at infinity, such as the G-Clarons. But they were designed as wide-coverage process lenses (and not as general purpose lenses for photographers), while the AM-EDs, at least according to Nikon's specs, seem to have somewhat narrow coverage. That Bjørn Rørslett reports that when he uses the 120 AM-ED for general photography for the 6x9 cm format that he has to use movements with care suggest that this lens doesn't have much coverage beyond what Nikon claims.
P.S. Here's the link to the specific frame on which Bjørn Rørslett reports on his use of the 120 AM-ED: http://www.naturfotograf.com/lens_LF.html
Walt, it depends on the design and implementation.
Two examples for you.
Rodenstock Apo Ronars are symmetrical process lenses. 4 elements in 4 groups dialyte type lenses, designed for use at 1:1 or thereabouts. As it happens, dialytes hold their corrections well at all magnifications. Rodenstock has published propaganda asserting that an Apo Ronar is better than any telephoto lens of the same focal length. I have one Apo Ronar that's too big and heavy for me to use, but I also have a pair of symmetrical (Nikon's designation) Apo Nikkors that I use, same design family as the Apo Ronar, and they're quite good at distance. Same goes for my two Apo Saphirs; heliar type, glasses might be symmetrical, although I think they aren't, but they can't be symmetric about the diaphragm like dialytes.
I use a little 100/6.3 Reichert Neupolar. This is a reversed tessar made for low magnification photomacrography with the Reichert MeF-2 metallograph. I use it on 2x3 at magnifications from 1:4 to 2:1. I've shot it at distance to see what would happen. Not a lot of coverage, nominal 6x6 at best, but at f/11 amazingly sharp at distance.
Moral, if any? When in doubt, ask the lens, not a guru or textbook.
Michael, I'm acquainted with Bjorn's site, but thanks for reminding me of it. I still think that AM-ED Nikkors are in the plasmat design family.
Cheers,
According to Nikon the AM-EDs have 8 elements in 4 groups so they're not plasmats exactly.
Sam, thanks for the correction.
Cheers,
Dan, I never said for or against the AM-EDlenses being a plasmats. They are not classic plasmats. You are probably correct that they are in the plasmat family -- it looks like Nikon split the inner elements into a cemented group, changing the design from 6 elements in 4 groups into 8 elements in 4 groups. They also reduced the coverage. The must have reasoned that a macro lens needs less angular coverage since it is used farther from the film, and traded off coverage for some other property.
Jeffrey, if you are looking for a lens that will do double duty as a macro lens and as a landscape lens, take a look at the G-Clarons and Fuj-A lenses. They won't be as bright for focusing since they are f9 lenses. Later (most) Fuji-As are multi-coated, all G-Clarons are single-coated. If the ED glass caught your attention, look at the Apo-Sironar-S.