Photomacrographic lenses, part 6
Version 1 Luminar 63 mm f/3.5,
|Version 3 Luminar 63 mm f/3.5,
aperture setting 2
|center of frame, 400 by 400 pixels crop||center of frame, 400 by 400 pixels crop|
|corner of frame, 400 by 400 pixels crop||corner of frame, 400 by 400 pixels crop|
To make it simple, I can see very little significant difference between Version 1 and Version 3 of the Zeiss Luminar 63 mm f/4.5. Assuming that you could focus with the necessary precision when using this lens in real-world situations (which you can't), and spend the time to do some pixel-hunting (time that probably should be spent for a better purpose), the newer version will give you a slightly "richer" picture when seen at a large magnification. This effect is the result of several minor improvements. Resolution, contrast, flatness of field, chromatic aberration near the picture edges and color fidelity have all been improved from version 1 to version 3 of this lens. Together with the fact that the tested versions of this lens are not parfocal and the differences noted in the introduction, these results confirm that the optical formula of the Luminar 63 mm was indeed re-computed between Version 1 and version 3 (probably, between version 1 and version 2, although lens coatings may have improved between Version 2 and Version 3). Thus, the differences among versions of this lens are more than a cosmetic redesign of the lens barrel. In practical use, however, it is simply too difficult to focus these lenses with the precision required to take full advantage of the resolution of which they are capable, and the improvements in contrast and color fidelity are very hard to detect in practical photographs.
There might be other advantages in choosing a Version 2, 3 or 4 of this lens over a version 1. For instance, lubricants in a later version are newer and have had a lesser chance to stiffen and dry out, and the lens may have been subjected to less use and abuse. However, this depends in large part on the conditions and climate in which a particular lens specimen has been stored. The diaphragm blades in Versions 3-4 are matte black, while in Versions 1-2 they are very shiny, literally mirror-like, and may potentially create flare by reflecting incoming light back to the front lens elements. The contour of the newer aperture ring is also slightly more comfortable to operate. The newer versions provide a slightly higher working distance (in my opinion, this difference is not significant, but it might be if every millimeter counts). Finally, sporting a "blue dot" Version 3 or 4 Luminar may win you some status and envy among the couple of dozens of photomacrographers who really appreciate the scarcity of these lenses. In accurate tests, the Version 3 of this lens will give you a slightly better image quality than the Version 1, but I doubt that the difference is significant in practical use of this lens. If you need this lens and have a chance of acquiring a Version 2, 3or 4 (and can afford the price), by all means do, but Version 1 does not deserve to be frowned upon. The latter, however, is a slightly different lens.
While the Macro-Nikkor 65 mm f/4.5 has a slight edge on the Version 1 Luminar 63 mm, any difference between the Version 3-4 Luminar 63 mm and the Macro-Nikkor is probably too small to matter in practice.
Important update: After using the above lenses, as well as other top-of-the-line photomacrographic lenses, for the photography of actual subjects with a specially modified photomacroscope (which, among other things, makes the notorious difficulty of focusing at high magnification a thing of the past, and guarantees that these lenses can produce the best image quality of which they are capable), I found that this page needs a significant update. While the above discussion remains fully valid and does not need to be corrected, it does not tell the whole story.
It turned out that all photomacrographic lenses in my possession display variable but significant amounts of axial (not radial) chromatic aberration. Radial chromatic aberration results in colour fringes around part of the outline of small bright objects (typically, blue and magenta fringes on opposite sides of the same object). This is the type of chromatic aberration commonly observed in general photography, especially outdoors. Axial chromatic aberration, instead, causes light of different wavelengths to be focused on different focal planes, rather than at different positions on the same focal plane. Axial chromatic aberration is rarely seen in general photography, but becomes a special problem in photomacrography, because of the extreme reduction in depth-of-field. All good photomacrographic lenses correct both axial and radial chromatic aberrations in their plane of focus, and normally you see little or nothing of these aberrations in the well-focused areas of photomacrographic pictures. Things get out of control, instead, in areas that are substantially out of focus. In these unfocused areas, bright points of light (e.g., reflections from pin-prick mirror surfaces) become horrendous balls with multiple haloes of different colours, multiple refraction and diffraction fringes, and an overall appearance like nothing you see in ordinary photography.
It is simply impossible to correct all types of chromatic aberration at all focal planes, at least in a lens that contains a small number (3-6) of optical elements. This includes all photomacrographic lenses. The correction of aberrations is always a compromise among different aberrations, and correcting the axial and radial chromatic aberration in the focal plane actually enhances it outside this plane. If you look carefully, you can actually see this in the above test pictures, especially in the corners of the original image's field-of-view. The Version 1 Luminar produces a visible radial chromatic aberration (one side of the white dust particles is blue). The Version 3 Luminar performs better in this respect, but the centre of the larger dust particles (which is out of focus, i.e., above the plane of focus of the picture) with this lens takes a cyan tinge, caused by axial chromatic aberration (with this particular lens, the tinge would be magenta for objects located out of focus in the opposite direction, i.e., behind the plane of focus). On the other hand, the older Version 1 Luminar displays a lower amount of axial chromatic aberration, because it does not attempt an equally extreme correction of radial chromatic aberration in the plane of focus.There is only so much you can do to correct aberrations in a Cooke's triplet lens design, and the Zeiss designers had to choose what they regarded as the best compromise.
In practice, this means that the Version 1 Luminar 63 mm may perform better, with certain real subjects that are partly out of focus, than the re-calculated and better-corrected (in the focal plane) Version 3 Luminar of the same focal length. Whether, and to what extent, this is also true of other focal lengths and versions of Zeiss Luminar lenses, remains to be seen. A further possibility that I did not test, but is suggested by my practical results with these lenses, is that axial chromatic aberration is a lesser concern if the lens aperture is closed 1-2 stops beyond the point at which diffraction begins to visibly affect resolution. Probably, it is not by accident that Zeiss recommended a narrower lens aperture than I would like to use, since film photography for scientific use was not expected to provide the same level of detail that is possible with current digital-camera sensors. Therefore, a higher amount of diffraction was tolerated, mainly as a trade-off against a higher depth-of-field and lesser chromatic aberration.
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