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04-08-2014, 12:13 AM   #1
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Accura Diamatic YS 105mm F2.5?

Is this lens worth buying an M42 adapter for? (Pentax brand of course)
I'm not even sure if that's the actual maker or a relabel brand.

I inherited this lens with a box of half junk along with my Super Program among other things years ago and wrote it off as some cheap off brand thing. But now that I am looking for a reasonably fast prime longer than 50mm for astrophotography among other things (already have other suggestions for that from another thread) so I pulled it back out and tried to look it up.
Apparently my parents used to have a Spotmatic that was replaced with the Super Program but the lens hung around for some reason along with an adaptall 2 28mm F2.5 with both M42 and KM adapters.

Best I could find was a few pics from one in this thread The 2013 Day Prime Challenge - Dyxum - Page 57 (cemetery shots half way down) which doesn't look half bad considering its adapted to a Sony A99 full frame, he noted that he botched the focus on the wide open shot which is too bad since I wanted to see the quality of that the most but the others seem awfully good for some cheap ancient off brand.

It seems to be in near like new condition and has an odd A/M switch ring to go from auto to manual aperture so it must be fairly old. The outer element is smaller than I would expect filter size wise for an F2.5 and its pretty small and light overall. Not sure if the slight yellow tint is old lens yellow or if its just an odd coating reflection assuming this thing is even coated.

On another note our miscellaneous 3rd party lens review section is a disaster, someone needs to go through and standardize the lens titles so they can be sorted by either focal length or brand because right now they are a random mishmash and the list has gotten too long for that. The "find focal lengths starting with" and the search function also both seem to be broken.

04-08-2014, 01:02 AM   #2
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I don't know about this lens, but I would say an m42 adapter is a great thing to have anyway
04-08-2014, 07:29 AM   #3
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It's a YS mount lens, so probably made by Sigma. These early Sigma lenses tend not to be very good, but then again 105mm was generally one of the safer focal lengths for these early 3rd party brands. It would probably be a decent performer, though not great. You don't actually need a M42 adaptor--just remove the YS mount by undoing the screws (see here: Spiratone YS Interchangeable Auto Mount Booklet) and use a T2 adapter (to K mount, obviously). T-mount adaptors are much cheaper, and it would probably be worth the $5 or so thus to give the lens a try.
04-08-2014, 09:33 AM   #4
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Hmm, I didn't even realize that YS was an adapter mount type like an adaptall.
I am seeing that the adapter on this one says YS-CS which suddenly concerns me but in looking it up a CS mount is 1"-32 thread so its impossible this is a CS as its definitely 42mm sized thread with whatever pitch.

Since I am told the Spotmatic was trashed because the threads "wore out" and wouldn't hold the lenses tight anymore I think I will just skip this whole mess as the adapter on it has just one single wrap of thread rather than the 3 or so complete wraps I see on other M42 stuff (like the M42 adaptall mount I have). It might have been what eventually wrecked the Spotmatic.

With the aperture ring half hidden by the beak on the front of DSLR's I don't really care for the manual stop down metering for M42 anyways so I think I will just stick to K stuff. My budget will thank me.


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