Dr. Harout wrote:AFAIK, there are no Alpha mount bellows ...
I am not aware of any ... fortunately we don't need them anyway.
Dr. Harout wrote:... so are we restricted to use only with adapters, i. e. Alpha to M42 screw mount, then the bellows and then a non-Alpha-mount lens.
Exactly. Alpha-mount lenses are not very useful on a bellows anyway because they don't have aperture rings.
My solution is to use the macro equipment from the Minolta SR system. As an adapter to the Alpha mount, I am using one of those infamous MF-to-AF adapters that use a glass element (two elements actually) to maintain infinity focus and thus also act as a 1.25× tele converter. I permanently removed the glass from mine (which was poor quality anyway) and widened the diameter of the hole with a file; it now serves as a 9.5 mm extension tube with Minolta SR mount on the front end and Alpha mount on the rear end.
Of course, you may just as well use M42 equipment on an M42-to-Alpha adapter.
Dr. Harout wrote:I use a M42 screw-mount bellows [...] and the lens should be M42 mount if not reversed.
And you have quite a collection of M42 lenses, haven't you? Some of them even are really high-quality, I think. Anyway, at magnifications beyond 1×, you're hardly ever using 'normal' lenses mounted via their regular mount. Instead, you're using 'normal' lenses in reverse mount on a retro adapter or lens heads with RMS mount on an RMS adapter ('normal' in this context is supposed to mean, lens designed for long focus distances, not for macro use).
Dr. Harout wrote:In case of mounting the lens reversely, then you should try to find an adapter from M42 to the filter size mount on that specific lens ...
Exactly. These adapters are not hard to find. For example,
Heliopan makes them; an E55-to-M42 retro ring currently is EUR 21.00. And you don't need one retro adapter for each filter size; instead you can use filter step-up or step-down rings. For regular use (i. e. to adapt filters), step-down rings often don't work well as they may cause vignetting. For macro use, you can step down seriously without being afraid of vignetting.
Dr. Harout wrote:And if it's an A-mount lens, then you should stick something in the rear of the lens in order to open the diaphragm ...
No. Just don't use Alpha-mount lenses in reversed mode, as simple as that. For use on a bellows in reversed mode you can buy cheap manual-focus lenses with aperture rings off eBay or at local swap-meets any day for just a few bucks ... the best are plain standard lenses, enlarger lenses, and moderate wide-angle lenses (the latter for really large magnifications beyond, say, 4×).
Dr. Harout wrote:Is there another decent way of doing it?
Errr ... you may try finding a Minolta AF Macro 3× - 1× lens ... but that's
very rare,
very sought-after, and
very expensive.
Regards,
Olaf