You're talking about a lens with a 67mm filter thread, right? To step down with a 52mm is extremely ambitious and probably won't work without heavy vignetting.
I can add this factoid: It is possible to add smaller-diameter supplementary plus-diopter close up lenses to tele lenses without any visible/noticeable vignetting effects. It won't work with normal or wide lenses. While I haven't added one to the Zeiss ZF 100/2 (gotta try that sometime), I have added the Nikon 5T and Nikon 6T to Nikon 135/2 AiS and 180/2.8 AiS lenses (both lenses are front-threaded 72mm) using a 72mm-62mm step down ring without visible vignetting in the resulting photos. As an alternative, the Zeiss ZF 100/2 can be used with a Nikon TC-14A teleconverter, which works well to increase image size with only a modest loss of resolution.
I've got a Canon EF 100/2 I step down from 58 to 55mm with no issues, even at MFD, but it doesn't focus down to 1:2, and I'm guessing close focusing will be more likely to show vignetting than .9m to infinity. Also, a 58 to 52mm step down ring causes mechanical vignetting in the corners from about 15m down to MFD, so I'd be careful about going down that far.
The good news is that step down rings are cheap for testing.
Keith B. wrote:
I can add this factoid: It is possible to add smaller-diameter supplementary plus-diopter close up lenses to tele lenses without any visible/noticeable vignetting effects. It won't work with normal or wide lenses.
There is a physical reason behind this phenomenon; in fact, by adding a close-up attachment filter to the lens, the focal length decreases BUT the angle of view decreases too (the higher the magnification, the smaller the AoV). Consequently, the AoV can be smaller enough to not cause vignetting.
Just to give an example. A (symmetric design, pupil factor = 1) 50 mm lens has an Aov = 47° when focused at infinity. At 1:2 the AoV is 32°; at 1:1 AoV = 24°.
However, OP didn't mention close-up filters, therefore, what Scott wrote is correct.
So, a question naturally arises: Which filter does the OP want to use on the 100/2 Makro-Planar (great lens, BTW)?