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Source for adapter with infinity focus?
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santiclaws View Drop Down
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Posts: 640 		Post Options Post Options   Quote santiclaws Quote  Post ReplyReply Direct Link To This Post Topic: Source for adapter with infinity focus?
    Posted: 10 October 2012 at 18:22
I have a couple of Alpha/M42 adapters (no AF confirm). One I picked up on ebay, one I got in trade with a member. Neither allows focus beyond 12-15 feet, I guess they are both a bit on the thick side. I tried with several different M42 lenses and two different bodies with the same result. I plan to try to sand them down a bit, but is there a reliable place where I can get adapters without having to do that?

Thanks
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Kilkry View Drop Down
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Posts: 630 		Post Options Post Options   Quote Kilkry Quote  Post ReplyReply Direct Link To This Post Posted: 10 October 2012 at 18:49
I bought one from "Uk.Delivery 2012" on ebay

It allows infinity focus w. my Volna 9 and CZJ 135.

Edit. I just saw that they only ship to Europe.

Edited by Kilkry - 10 October 2012 at 19:34
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ifreedman View Drop Down
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Posts: 1792 		Post Options Post Options   Quote ifreedman Quote  Post ReplyReply Direct Link To This Post Posted: 27 October 2012 at 05:40
Did you ever find an adapter that works?

Note: I was the member that sent him an adapter in a trade. The curious thing is that similar adapters ( I don't think I tested that specific one) seem to focus fine to infinity on my a33. So I find is odd that they don't reach infinity on his camera. I'm not convinced that the problem is the adapter thickness. There are several Chinese companies on ebay that sell $2 adapters w/ free shipping. You could try some others, although it will take a couple weeks to receive in the mail.

Wish I could offer you more advice, but without knowing exactly what the problem is, I'm not sure what to suggest.

Ian
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kevan View Drop Down
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Posts: 127 		Post Options Post Options   Quote kevan Quote  Post ReplyReply Direct Link To This Post Posted: 30 November 2012 at 16:07
I'm in the same boat. I just picked up a couple of Takumars (28mm and 50mm) and neither will focus beyond 15feet with an ebay cheap adapter on an A65.

Like Ian, I used to have an A33 which worked fine with a Takumar 55mm I had back then.

Very strange - if anyone has an answer, I would be very interested too.
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Posts: 20 		Post Options Post Options   Quote SinfulSaint Quote  Post ReplyReply Direct Link To This Post Posted: 01 December 2012 at 10:13
Take the adapter and sand it down on a flat surface. Glass preferably.

Sand the adapter surface that touches the lens on the bottom/screw side.

Shave off some .25 or more. This is a hit and miss situation.

This allows the lens to screw in more, reach the registering distance and therefore focus to infinity.

Each and every of my lenses was soft at f2 @ ∞.

Now it works fine. Nice and sharp at f2.
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Bob Maddison View Drop Down
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Posts: 930 		Post Options Post Options   Quote Bob Maddison Quote  Post ReplyReply Direct Link To This Post Posted: 01 December 2012 at 11:41
The lens register distance for the M42 is 45.46mm whereas the lens register distance for the A Mount is 44.60mm. This means the the M42 lens is 1.06mm too long for an infinity focus on an A Mount camera, especially as any adapter has itself a finite thickness. Nothing you can do other than grinding down the M42 flange by about 1.5mm will work.

Only an adapter with a built in lens to alter the M42 lens Register Distance will give you infinity focus. This lens acts as a short teleconverter and will also change the focal length; it will also reduce IQ. Minolta used to list one which had, I believe, a focal length extension of 1.5x. If you are going to use an adapted lens, then keep it for close ups and forget about infinity.

On the other hand, a camera with the Sony E Mount will easily accept an adapted M42 lens.
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neilt3 View Drop Down
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Posts: 549 		Post Options Post Options   Quote neilt3 Quote  Post ReplyReply Direct Link To This Post Posted: 01 December 2012 at 12:19
Originally posted by Bob Maddison Bob Maddison wrote:

The lens register distance for the M42 is 45.46mm whereas the lens register distance for the A Mount is 44.60mm. This means the the M42 lens is 1.06mm too long for an infinity focus on an A Mount camera, especially as any adapter has itself a finite thickness. Nothing you can do other than grinding down the M42 flange by about 1.5mm will work.

Only an adapter with a built in lens to alter the M42 lens Register Distance will give you infinity focus. This lens acts as a short teleconverter and will also change the focal length; it will also reduce IQ. Minolta used to list one which had, I believe, a focal length extension of 1.5x. If you are going to use an adapted lens, then keep it for close ups and forget about infinity.

On the other hand, a camera with the Sony E Mount will easily accept an adapted M42 lens.


an m42 lens on a sony camera will work fine up to and including infinity , without any extra lens elements ,providing the correct thickness adapter is used.
mine all work fine.

as you have noted the lens register on an m42 lens is 45.46 mm and our cameras are 44.6mm away from the sensor.
this means that as long as the adapter is no more than 0.86mm thick the lens will still be the same distance from the sensor.so infinity focus is maintained . any thinner and you will focus beyond infinity.

i have seen adapters that are too thick and act as a mini extension tube.these are no good.


edited to correct bad math's !

Edited by neilt3 - 01 December 2012 at 13:27
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neilt3 View Drop Down
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Posts: 549 		Post Options Post Options   Quote neilt3 Quote  Post ReplyReply Direct Link To This Post Posted: 01 December 2012 at 12:29
just as an aside , this is why m42 lenses can be used on any make of dslr without an extra lens ,apart from nikon whose lens registar is 46.5mm .
pentax user's need to use a threaded inset to convert K mount to S mount for the m42 lenses to maintain infinity focus.the k mount adapters with a flange push the lens out too much.
see my photostream on flickr;
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Bob Maddison View Drop Down
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Posts: 930 		Post Options Post Options   Quote Bob Maddison Quote  Post ReplyReply Direct Link To This Post Posted: 01 December 2012 at 13:08
My apologies, I got the situation the wrong way round. I was thinking about using a MD lens (register distance 43.72mm) on an A Mount camera. The Minolta adapter I referred to was in fact for the MD lenses.

Yes indeed it is feasible to use a simple M42 adapter to the A Mount camera, but the metal (i.e. spacing) thickness must not exceed 0.86mm. Grinding or sanding an adapter down is possible, but it is difficult to ensure a truly flat surface and retain uniform thickness. There is no problem trying several different cheap adapters, if they cheap enough!
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neilt3 View Drop Down
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Posts: 549 		Post Options Post Options   Quote neilt3 Quote  Post ReplyReply Direct Link To This Post Posted: 01 December 2012 at 13:39
Originally posted by Bob Maddison Bob Maddison wrote:

My apologies, I got the situation the wrong way round. I was thinking about using a MD lens (register distance 43.72mm) on an A Mount camera. The Minolta adapter I referred to was in fact for the MD lenses.

Yes indeed it is feasible to use a simple M42 adapter to the A Mount camera, but the metal (i.e. spacing) thickness must not exceed 0.86mm. Grinding or sanding an adapter down is possible, but it is difficult to ensure a truly flat surface and retain uniform thickness. There is no problem trying several different cheap adapters, if they cheap enough!


your quite right about the 0.86mm thickness , don't where i got my math's from !
edited my earlier post to avoid confusion.

there are plenty of the correct thickness adapters about , they look very thin , like thick paper.
the "wrong" ones do look very chunky by comparison and are quite easy to spot.
see my photostream on flickr;
http://www.flickr.com/photos/neilt3/
C & C welcome.
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leonbidon View Drop Down
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Posts: 453 		Post Options Post Options   Quote leonbidon Quote  Post ReplyReply Direct Link To This Post Posted: 01 December 2012 at 14:11
As far as I know the flange focal distance for the M42 is indeed 45.46mm. But for the Minolta/ Sony Alpha mount it's 44,50mm and not the mentioned 44,60mm

( http://en.wikipedia.org/wiki/Flange_focal_distance )

This gives an adapter-thickness of 0,96mm and not 0,86mm.

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alpha_in_exile View Drop Down
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Posts: 2211 		Post Options Post Options   Quote alpha_in_exile Quote  Post ReplyReply Direct Link To This Post Posted: 01 December 2012 at 15:42
Hey folks - at the top of this forum is a 'sticky' thread specifically re: adapters & whether they focus to infinity. Granted the thread title ("M42 adapters: results summary") might be unclear.

I used one of the adapters from that thread (sorry I don't recall which), without a problem.

Some of the info might be out of date, but one can always add with your own experience.
-- Matt
A900, A100, Min 24/2.8, Min 50/1.4, Tam 70-200/2.8
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