p.5 #1 · Cosina Voigtländer APO-Lanthar 90/4 VM officially announced for August release
Michael Gordon wrote:
Curiously if one place 25 mm extension of the lens that should lead to a mag of almost exactly 0.56 as well. That is what I do. The lens seems to behave nicely with extension. I do not recall that the diopter was achromatic and I think it was not. Anyone know for sure? Diopters are extremely convenient but not a fan of non achromatic ones.
I don't like the 90 as much as the CV 180/4 but I still like it. I would be interested in an updated 180 mm.
I haven't seen or used the Voigtlander-supplied close-up lens, but I have tested two different achromatic close-up lenses with the 90/3.5: the Kenko AC4 with +4 diopters and the NiSi NC with +5 diopters (official specs in each case). They both work well with the 90/3.5, which is a bit unusual because both of these have a tendency to cause severe linear distortion with other lenses-- one of the reasons that I typically prefer to use extension. The unusually good performance of the 90/3.5 with diopters may explain why Cosina felt that a close-up lens would pair well with this lens.
Note that these diopters cause the effective focal length to shrink, which is important to keep in mind when setting up the IBIS on the camera. The "naked" lens has a measured focal length of 88mm at infinity and 89mm at the minimum focus distance (which is a bit atypical; usually the gap is larger, and it is often in the other direction). The two close-up lenses I mentioned lower the effective focal length at maximum magnification to 67mm and 64mm respectively, while raising magnification to .704x and .791x. While the 90/3.5 works reasonably well with this setup I have better macro lenses, so I tend not to use it.
p.5 #2 · Cosina Voigtländer APO-Lanthar 90/4 VM officially announced for August release
I too am interested in how this compares to the 90/2 APO Ultron. I am looking for an additional lens for my travel kit. I know the size difference but the 90/2 is still small compared to the xf90/2 from Fuji .
p.5 #3 · Cosina Voigtländer APO-Lanthar 90/4 VM officially announced for August release
dan98 wrote:
I haven't seen or used the Voigtlander-supplied close-up lens, but I have tested two different achromatic close-up lenses with the 90/3.5: the Kenko AC4 with +4 diopters and the NiSi NC with +5 diopters (official specs in each case). They both work well with the 90/3.5, which is a bit unusual because both of these have a tendency to cause severe linear distortion with other lenses-- one of the reasons that I typically prefer to use extension. The unusually good performance of the 90/3.5 with diopters may explain why Cosina felt that a close-up lens would pair well with this lens.
Note that these diopters cause the effective focal length to shrink, which is important to keep in mind when setting up the IBIS on the camera. The "naked" lens has a measured focal length of 88mm at infinity and 89mm at the minimum focus distance (which is a bit atypical; usually the gap is larger, and it is often in the other direction). The two close-up lenses I mentioned lower the effective focal length at maximum magnification to 67mm and 64mm respectively, while raising magnification to .704x and .791x. While the 90/3.5 works reasonably well with this setup I have better macro lenses, so I tend not to use it. ...Show more →
Doing a bit of digging, it seems the CV CU diopter is +3 single element lens but closely matched to the optics. I bet a good achromatic 2 element version of the same strength may do as well. The 25 mm extension may result in more field curvature but that doesn't usually matter much for macro. I initially poo-pooed CU diopters but found well matched ones can be great and super convenient. Good point about the IBIS setting and very weird about the lack of FL shortening for close focus--nice feature to retain working distance.
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