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10-21-2009, 04:12 PM   #1
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Using Non-INF adapters help

I am wanting to get a 50mm -85mm M39 or M42 lens for portraits. subject will be no more than 7 feet away
Question:
Will these adapters focus to in the under 10' range? I am looking at a Jupiter 8, 3, or 9 (50mm/2, 50mm/1.5, 85mm/2) or an Industar 61/LZ,

2nd Question
At what f/stop does the AF confirm stop working with single ring stop down lenses...f/5.6 I think?

10-21-2009, 04:18 PM   #2
Damn Brit
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This is not about style or technique, please be careful where you post.
Thanks
10-21-2009, 04:29 PM   #3
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QuoteOriginally posted by Damn Brit Quote
This is not about style or technique, please be careful where you post.
Thanks
Opps...I'll do better
10-21-2009, 06:15 PM   #4
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QuoteOriginally posted by arbib Quote
I am wanting to get a 50mm -85mm M39 or M42 lens for portraits. subject will be no more than 7 feet away
Question:
Will these adapters focus to in the under 10' range? I am looking at a Jupiter 8, 3, or 9 (50mm/2, 50mm/1.5, 85mm/2) or an Industar 61/LZ,
It depends on the thickness of the adapter flange and the lens in question.

QuoteOriginally posted by arbib Quote
2nd Question
At what f/stop does the AF confirm stop working with single ring stop down lenses...f/5.6 I think?
The AF requires a certain amount of light to work, so failure to lock focus is not so much a matter of aperture, but how much light is available to the sensor. Note that it is usually best to focus wide open and stop down to expose. A bit cumbersome, but part of the penalty of using M42 lenses on a K-mount body.

Steve

10-21-2009, 06:20 PM   #5
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May I ask why you consider the flange-type adapter? If it is cost, the genuine Pentax adapter is not that much costlier, and your "problem" is solved.

About when the AF-confirmation stops working - the number that commonly used is F/5.6. But I know for sure that at F/6.3 it still works. At F/8, it still works but needs something contrasty to lock on.
10-22-2009, 05:05 AM   #6
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Here's the numbers.

The farthest focus distance with a registry error of mm millimeters for a lens with focal length F millimeters is:

Distance = F(F+mm)/mm

So for a 50mm lens and a 1mm error the most distant focus is:

50(50+1)/1 = 2.55 meters, for a 2mm offset it is 1.3 meters.

I just measured the thickness of a flange, it is 1mm so you'll be ok.

Dave in Iowa
10-22-2009, 06:22 AM   #7
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I have a few of the flanged adaptors that came on misc. used lenses. And a few Tak's. that go past inf. focus that will work at infinity. My old tak. f4- 300mm works just fine with one so I just leave one on it. couple of others do also. The flanged adaptor is some what simular to using an extenchion ring for macro. simply shortens focal distance. Hope this helps. jim
10-22-2009, 06:32 AM   #8
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I would stay away from the M39 lenses. Both the 85/2 and Industar 61 come in M42 mount. By using the Pentax M42 to K mount ring, they will focus to infinity, and down to their minimum. The Industar 50-2 pancake also comes in M42 mount.

10-22-2009, 01:14 PM   #9
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QuoteOriginally posted by SOldBear Quote
May I ask why you consider the flange-type adapter? If it is cost, the genuine Pentax adapter is not that much costlier, and your "problem" is solved.

About when the AF-confirmation stops working - the number that commonly used is F/5.6. But I know for sure that at F/6.3 it still works. At F/8, it still works but needs something contrasty to lock on.
I have been looking on eBay, and now there are 3, I think, But, I am moving, so spending $10 for a flange type, over around $35 for a Pentax brand is a savings.

I have an 85mm T2 f/1.8 without an Iris (it has been removed)...and it now a lens for "Special" soft/glow effects...I like the cropped 85mm, but want a better lens. It is just for studio use too.

I had another thread about using a M42/Pk..as far as what what restrictions I'd have. And I read a good blog on this too.

So, I guess I just need a flange type my use at the moment...
Thanks
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