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Sigma 300mm f4 YS with... extra glass OM adapter?
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PostPosted: Wed Aug 24, 2022 4:16 pm    Post subject: Sigma 300mm f4 YS with... extra glass OM adapter? Reply with quote

I got a Sigma 300mm f4 YS in the mail today, which appears to be in very good condition optically and mechanically. Iris works, no scratches or haze up front, both helicoids work just fine.



Yet I noticed with everything looking mint and the rear of the lens sealed with a glass element, there was grime close to the rear group. It looked like the sort of grime that falls down the recessed rear of a lens like this, but how could it do that if it was 'always sealed'?

Well I knew the facts here, I just couldn't believe what I was seeing. I knew YS mounts should just unscrew, they never had glass 'sealing' the rear like this, and 200/300/400mm lenses like this always had quite recessed glass. Clearly something was going on...





As you can see, there was no aperture stop down lever or button- just the release one.

It would not unscrew, so off came the rear flathead screws of the mount- quite easily:




Aha- it certainly was a negative group! I haven't decided on the number of elements yet. Clearly coated (blue). No markings.





So this where we're at currently. I will be getting the hairdryer out as it still won't unscrew. I have no idea who did this and why.

I have read online Sigma never made an Olympus mount YS adapter. But for a lens with a manual aperture toggle, why wouldn't you just use a T-Mount adapter? Probably didn't realise in some way. No need to blame anyone.

If this does come off readily and was just a little stuck, I might understand that someone had a YS - OM adapter made and was trying it out on various lenses. If it's really glued in here, for this specific lens, then I have even more questions!


PostPosted: Wed Aug 24, 2022 5:02 pm    Post subject: Reply with quote

Weird piece!

http://forum.mflenses.com/spiratone-ys-interchangeable-auto-mount-booklet-t32619.html

and

https://www.butkus.org/chinon/y-s_mount/ys.htm


PostPosted: Wed Aug 24, 2022 9:34 pm    Post subject: Reply with quote

Well....







After some hair-drying and isopropyl alcohol, this was revealed to not be a threaded connection at all.

No... they had filed off the T-Mount threads. The straight-line marks on the mount are a byproduct of this.

Then they must've laid some glue down (EDIT: you can spot the glue in the first image), push-fit an M42-OM adapter (which comes out of this unscathed) and called it a day.

I can only guess there was extensive damage to the threads which justified doing this. But I am out of options bar a mount replacement here.


PostPosted: Thu Aug 25, 2022 1:07 am    Post subject: Reply with quote

Glue on a T2 adapter...


PostPosted: Thu Aug 25, 2022 9:07 am    Post subject: Reply with quote

Interesting mystery story resolved Smile !


PostPosted: Sat Aug 27, 2022 4:32 pm    Post subject: Re: Sigma 300mm f4 YS with... extra glass OM adapter? Reply with quote

eggplant wrote:

I have read online Sigma never made an Olympus mount YS adapter.


The YS /OM mount DID exist (100% sure, i had one !)


PostPosted: Sun Aug 28, 2022 4:16 am    Post subject: Reply with quote

This Sigmatel 135/1.8 lens for sale has one, slightly on the high side pricewise though...

https://www.ebay.com/itm/394131334259?


PostPosted: Mon Aug 29, 2022 12:38 pm    Post subject: Reply with quote

Alun Thomas wrote:
This Sigmatel 135/1.8 lens for sale has one, slightly on the high side pricewise though...

https://www.ebay.com/itm/394131334259?


You can easily recognize the YS OM mount (as opposed to the fixed om mount) by the fact that it has a wide chromed ring like the fd breech lock ring