Amongst my collection of Soviet glass, I have a very nice ZM-5SA ("3М-5СА") 500mm f/8 catadioptric / mirror lens in M42 mount. It works a treat on my Sony A7 MkII, and produces beautifully sharp and detailed photos, considering the poor reputation of this type of lens.
I also have two different Soviet 2x tele-converters... a TK-2M and K-1.
Today, I tried out the ZM-5SA with each of the tele-converters, and immediately noticed extreme vignetting... not just strong light fall-off, but the type where the image circle isn't covering the whole of the sensor. The same thing happens with both converters.
I have SteadyShot turned off on the camera, as I know this can have an effect, but in any case this vignetting is too strong to be caused by that.
I'm thinking it might be caused by the M42 adapter, but the type I'm using has no obvious internal pieces that would restrict the optical path.
Does anyone else have experience with this lens and / or these teleconverters on full frame? It would be nice to rule out whether this is due to the lens + TC combination, or if the problem could be with the adapter and/or camera.
The first photo below shows a white wall capture without the TC, and the second one, with...
Thanks in advance