M42 Adapter: Can this type focus infinity?

jocko_nc · 05-07-2009, 09:12 PM

I borrowed a photo from Ebay... All rights to the owner who is shown.

The seller says this design will allow for infinity focus. ???. I know the mount distance of the M42 and K are the same: A perfect adapter of a flange design would require a thickness of zero. Is there anything different with this one? Is there an offset that the others do not have? Is that even possible?

The last two adapters I had were both third-party, one aluminum similar to this and one internal with the removal tool. The internal was hard to remove. I do not recall that the aluminum adapter did not reach infinity, though I may have unwittingly not shot anything more than about 50m with that lens. ???. Maybe I got lucky.

I was ready to get the OEM adapter, but saw this ad and was curious.

*Rense* · 05-07-2009, 09:26 PM

It doesn't look good to me! But possibly others know better....

*F16* · 05-07-2009, 09:34 PM

Technically speaking it's not really possible, at least it would not be with many/most? lenses (some lenses will focus slightly past infinity). As you say, M42 and K mount have an identical register distance. There could be some sort of very slight 'inset' that may allow 'some' M42 lenses to seat deep enough to have the proper register, but I think it'd be rare that you'd find M42 lenses that are narrow enough at their back face to fit inside that 'inset'. Hope you understand what I'm saying... Best case scenario, an adapter like this would be acting as something around 1.5-2mm extension tube, closer to 3mm would be realistic. So unless your lens can focus a noticeable amount past infinity, you can't reach infinity. With a long telephoto it might actually work fine in many cases, but with shorter lenses it will become increasingly apparent.

BTW, even with this know issue, I have been planning to order at least one of these for awhile, I have 3 genuine Pentax adapters already but there are times when I know I won't need infinity focus and an adapter like this is easier to work with.

stevebrot · 05-07-2009, 10:05 PM

Short answer...No...

The wide flange will make infinity focus impossible. The best advice I can give is to spend the extra money and get the genuine Pentax adapter.

Steve

RioRico · 05-08-2009, 05:31 AM

I'll ditto Steve. Official Pentax adapters work, will infinity-focus, won't get stuck, will be easy to remove. Non-official 'infinity focus' (rimless) adapters WILL get stuck, WON'T be easy to unhitch. I've removed the offending springs from all mine and dedicate them to specific M42/M39 lenses. Non-infinity-focus adapters (like the one pictured) are useful only if 1) you have a lens that focuses past infinity, like my old Spiratone 400, or 2) you don't care about infinity, like with a portrait or macro lens, or macro bellows or tubes. Using that adapter with my Jupiter-9 insures that backgrounds are never annoyingly sharp, eh?

Mike Cash · 05-08-2009, 05:49 AM

Originally Posted by jocko_nc

The seller says this design will allow for infinity focus.

The seller is a lying S.O.B.

Any of a hundred or more posts here on Pentax Forums regarding the M42 adapter could have cleared that up.

Out of curiosity, would the cost of the two third-party adapters you bought in order to save a couple of bucks added together be more than the price of just buying an OEM adapter to begin with?

jocko_nc · 05-08-2009, 06:58 AM

That confirms what I thought. Thanks.

I got rid of my couple of M42's last year, never figured to need an adapter again. Now, I have a significant new toy in M42. Its OEM for me.