Schneider 80mm XL... smaller, faster, sharper?greenspun.com : LUSENET : Large format photography : One Thread
Now that Schneider has posted the theoretical MTF curves for the new 80mm XL, I am really curious about the performance of this lens. I should preface this question by noting that I am interested in the 80 for use on 6x9 roll film, and that I have the 110XL for 4x5 and find it to be a wonderful performer.
The curves seem to show that at f/8, MTF fall off is so dramatic as to make the lens very soft in the corners of a 6x9 (~50mm off axis). No curves are posted for f/11 or f/16 which would be the sweet spot for use with roll film formats.
At f/22, the off-axis performance is better, but the 20 lp/mm the tangential performance still falls off pretty markedly.
Comparing this to the MTF curves from Rodenstock on the 75mm f/4.5 Grandagon-N, the Grandagon seems to provide better evenness of performance across the field. For example, at 50mm off-axis, at f/22, the Grandagon curves show 60% sagittal and 45% tangential, vs. about 65% sagittal and 32% tangential for the Schneider 80mmXL.
So it's not clear that at f/22 the XL is any better than the existing Grandagon-N (although the XL is about 150g lighter). My main concern is performance at f/11-f/16, where it is not at all clear that the 80XL will even equal the Grandagon-N.
Schneider doesn't show longitudinal chromatic curves, so it is hard to compare potential color fringing.
So, as soon as some people have the 80, I would love to hear about real world performance. And I would love any input from Schneider folks or Rodenstock folks, or optics guru's on whether the 80XL really represents any improvement over the existing 75mm Grandagon.
BTW, I don't fret about such things with 4x5, but with roll film, I find the tolerances are tight to produce sharp 20x24's, and it looks like the 80mm XL is going to be 30% more costly than the Grandagon.
-- Glenn Kroeger (email@example.com), November 03, 2000
Glenn: Your point about image degradation off-centre is quite true. For the 80XL, at infinity and F22, it does degrade severely after about 50% of the maximum height( i.e. 53mm from centre). At this point, the tangential response is only 30% but the radial is 55% at a spatial frequency of 20 L/mm. My real world experience with and MTFs for my 90mm Super Angulon, which I consider an extremely sharp lens on 4X5 make interesting comparison with the 80mm XL MTFs. A t infinity and F22, the 90mm SA, at 53mm off centre, shows identically the same response as the 80mm XL for both tangential and radial responses. The 110 XL does post a much better performance than the 80XL but because of the longer focal length and slightly narrower angle of view of the 110XL compared to that of the SA 90, I am not sure that we are comparing apples and apples. Your point that at F8, the 80XL does drop off drastically is true, but the matter is that in spite of its F4,5 maximum opening, this lens was intended to deliver optimum quality at F22, Certainly, at F22 its quality is quite comparable to the 90 SA MTFs which in my real world experience is an outstanding lens. The other lens worth comparing is the 90mm SA XL which delivers marginally better MTF at 53mm off-centre than the 80mm XL at F22 and at infinity. Because the separation and relative position of the response lines are similar, one can conclude that sharpness and contrast will also be similar. Interestingly, the responses of the two 90mm lenses and those of the 110XL at F5,6 are similar, and at this opening, these lenses are sharper (indicated by the closeness of the two response lines) than at other openings, at least on the portion of the image circle where the response is substantial. The 80mm XL however lags slightly in this respect. Generally, I prefer to place more emphasis on the separation between the two responses, i.e. radial and tangential, without ignoring the contrast response, -as indicated by the height of the lines in the graph. My reason for so doing is that closeness in radial and tangential responses is related to sharpness. (Zeiss and Rodenstock communications). Contrast can be manipulated in the process of image-making, while sharpness can be fudged by software but not really improved. All of this within reason, of course, there would be no point in having sharpness as without contrast there would be no image.
Because your interest in the 80XL is mainly in what happens on a narrower image circle, given that the image circle for this lens is 212mm, one would be looking at MTFs up to the region of 50% of maximum image height only, (105mm IC) if your MF camera has a no movements and slightly more according to the cameraBs movements. In the 50% region these MTFs are about typical for wide-angle lenses at F8. However, because your use is MF you probably would want to look at MTFs for 30L/mm spatial frequencies, rather than 20L/mm, which Schneider provides, and which, it is an acceptable yardstick for 4X5. Taking that into account, it is possible that you may find technically better lenses among those made for 6X7, which do not have to be designed for such large ICs. I doubt however that the difference between the 6X7 lenses and the 80XL will be dramatic enough to not justify purchasing the 80XL, or conversely buying the 80XL if you already have a lens for MF in that F. The XL offers the convenience of larger maximum aperture, -which some photographers complain is a problem with wide-angle lenses, as well as mid-point positioning between the 75 and the 90 and you back-pack and want to avoid carrying two. If those conveniences are important, it is a buy. Personally I do not think that this lensBs performance alone warrants the expenditure if you have the 75 or 90 SAs. Good luck and please forgive the length.
-- Julio Fernandez (firstname.lastname@example.org), November 03, 2000.
Glenn I have one on order, should get it later this month. I'll send you an original chrome from it and you can judge for yourself.
-- lloyd chambers (email@example.com), November 07, 2000.