Designed lens sharpness.
I've been looking a particular Pentax macro lens that is said to have extremely high sharpness. It's a A 50mm f/2.8. It's got me to thinking about lens designs. A lot of Macro lenses have very high resolution. These lenses are usually in the f/2.8 to f/4 range, but there have been some very good one at the f/2 and f/2.5 mark as well. So my question is this: Do lens designers have the ability to make traditional, non macro, lenses spectacularly sharp but do so because they would have unpleasently high sharpness, or perhaps because there would be too great a difference in sharpness between apertures, or is there something "magical" about macro designs that allow for such high resolution values.
Do lens designers limit gross resolution in order to achieve some sort of balanced lens design?
PS: I use the terms resolution and sharpness pretty loosely here, but I think my general point in pretty clear.
To my understanding macro lenses don’t yield better resolution and sharpness (it would be better to employ the MTF concept here) than lenses of the same focal length within the same class.
It is just that both types of lenses are calculated for different imaging scales resp. object distances. Concerning the issue of macro lenses yielding the same image quality at infinity as general purpose lenses I found that one renown lens company made contradictory statements on this issue…
Concerning an intented reduction in sharpness I refer to the design of lenses for digital capture. There at high resolution-frequencies which would be the same the very sensor would produce spurious resolution the lenses are designed to have a sharp fall-off in transmitted contrast. This is not an issue in analogue photography, and thus the lenses for this field can be calculated for maximum response at the highest possible frequencies. (Only limited by their price.)
And there are still those soft focus lenses which are calculated to yield in one way or another a high degree of spherical abberation.
Last edited by AgX; 11-01-2007 at 08:11 PM. Click to view previous post history.
Usually as lens opening go up one F-number (say from F2 to F2.8) the price go up around twice. So F2 is around twice expencive as F2.8 (similar focal length).
When F2.8 is twice more expensive than F2 something is missing. It is optical and mechanical design, glass kind, tolerances in manufacturing, mechanical design,... Lens price do not go by lens quality it go by lens production cost.
When you acouint what is above, (Zeiss Planar F2/50 mm ZF Macro) is around four times more expensive as (F1.4/50 mm Planar).
Standard lenses are corrected for indefinite, easy job. But who use it at indefinite? It is why quality is down, plus lower cost to develop, plus lower cost to manufactur, plus lower cost for materials (glass, to answer you question).
Macro we have from Leica and Zeiss are not real macro, but rather close-up lenses. They are also made from the best glasses and so very expensive. Something like Ford make different cars of different quality, for different pockets. However these macro (super lenses) are not very good for portrait, or we have to attach Zeiss Softar on it....
In the early 1970s I did a crude, but critical, resolution test of about 30 quality lenses for 35mm cameras and enlargers. Four were definitely sharper: Leitz 50mm f/2.8 Elmar, 45mm f/2.8 GN-Nikkor, Micro Nikkor 55mm f/3.5, and EL-Nikkor 50mm f/2.8. The first two were four element Tessar formulas, the latter two were six element. Faster lenses, like the Nikkor 50mm f/1.4 and f/2 and the Leitz Summicron f/2 were slightly less sharp wide open. All lenses designs are a compromise between sharpness, speed, macro capability, focusing distance, and cost. A few very fast lenses are optimized at widest apertures.
You asked a critical question , problem is to know what designer can do and can not do ? How much art is there at lens design or how much it depends on more precise carving of glass and better more expensive glasses.
I am not a scientist but i learned something about 1942 zernike inventions and 1953 nobel prize. he had been found a easier way to balance many errors or corrections in a faster way. if it is not all mathematics , who says lets put some spherical aberration in to the design ? Which aberrations and how much of them put artificially in to the design ? I want to learn that.
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Many macro lenses are designed to optimally render two dimensional objects (ie - paper, paintings, anything flat) well on 2-dimensional film, but not designed to record 3-D objects well in 2-D.
I'm only remembering what I've read from people who know the engineering of optics far better than me. Don't quote me as an expert.
What I've read is that a macro lens tends to flatten out the rendering of a 3-D object, as if it were 2-D.
Lenses are only tools. There is no one lens that can do it all. Also, I believe the notion that lenses should be selected for their 'sharpness' is over rated, when there are other features to be considered.
Thats a very simplistic answer.
Macro lenses are designed and optimised for close up work typically 1:1 to 1:5
Compared to a similar focal length normal lens reversed a macro lens will give better depth of field and sharpness at the same apertures. They are not particularly designed for flat field work after all the medical Nikkors etc are used to photograph 3-D objects, and most are designed for all types of close-up applications. I've never heard of any nature/wildlife photographers complaining that their macro lenses caused flatter rendering of their images.
However Flat field process lenses designed for "Process Cameras" are different, but they are not designed for normal film camera use.
Last edited by Ian Grant; 11-02-2007 at 07:52 AM. Click to view previous post history.
Originally Posted by Pinholemaster
Nearly all lenses are designed to image a plane on a plane. You may be thinking of process lenses; they're intended to be used in applications where curvature of field can't be tolerated, so may have better field flatness than lenses not made for such exacting applications.
And macro lenses don't flatten. They are typically optimized, as Ian has already pointed out, for near distances. Prints made from negatives taken with a lens that's long for the format and viewed at normal viewing distance exhibit flattened perspective, but that has nothing to do with the conjugates the taking lens was optimized for.
Slower lenses are easier to control aberations and macro lenses will focus on a flat plane if they are designed to do so. Field flatness is not a design optimizarion with faster lenses usually.
There's much discussion of glass in this thread but I'm wondering what bearing, if any, the number of aperture blades has on the original question, i.e., sharpness (as opposed to bokeh etc.).