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Biotar unable to infinity focus

Posted 17/01/2012 - 19:53 Link
Hi

I cannot focus my Biotar lens to infinity, even though I have a genuine Asahi Pentax mount adaptor (or so I hope: it fits flush and it has the words ASAHI PENTAX JAPAN engraved on the front). The actual lens model is: Carl Zeiss Jena Biotar f2/58 mm (10 Blades). Has anybody experienced this problem with their Biotar lenses? Is there a way out?

Thank you ever so much
Pentax K-X, Carl Zeiss Jena 1Q Biotar 2/58 mm (10 Blades)
bento2
Posted 23/01/2012 - 04:46 - Helpful Comment Link
Valentinus,

Have a look at c't Digital Photography 4 (2011) They have a great article on using M42 lenses and adaptors on bayonet mount cameras. Seem like there are certain combinations which will not focus at infinity, or conversely focus at infinity a long way before the lens marking.

Conclusion is that it is really a matter of trial and error as to which combinations of lens and adaptor work, and which don't.
DoctorJeff
Posted 24/01/2012 - 09:39 - Helpful Comment Link
bento2 wrote:

... there are certain combinations which will not focus at infinity, or conversely focus at infinity a long way before the lens marking ....

Conclusion is that it is really a matter of trial and error as to which combinations of lens and adaptor work, and which don't.

Like bento2 asks - do you mean that the Biotar will not focus at infinity, or that the infinity marking on the lens does not come to the "12 o'clock" position? These are two different problems. A third problem is that the focus ring will turn so that the Infinity mark has gone beyond the index mark.

I had an M42 lens that would not mount with the index mark at 12 o'clock on any (yes, any) M42 body - let alone an adapter. I have an M42 lens that visibly wobbles when used with an adapter - in this case the lens has pulled tight on the adapter before it has contacted the lens-mount flange. You need to define your terms very precisely, to determine if this is a lens or a mount problem.
Geoff
Water can wear away a stone - but it can't cook lunch
X-5
istDS
K2000
P50.
Lenses Digital: 50-200, 18-55 KAF: 28-80.
Lenses KA & K: SMC-KA f2.0, SMC-K f1.4, SMC-K f1.7 Tokina KA 28-70 , SMC Pentax 70-210 F4, Sigma KA 75-300 , Hanimex 500mm Mirror, and the Tamron Adaptall-2 stuff.
and then there's all the M42 kit, and the accessories ...
Posted 04/02/2012 - 14:19 Link
Hi Doc and Bento and thank you very much indeed for your kind and very useful answers. Sadly, I don't think I'll have a chance to verify what the real problem is, since I've lost both my K-x and Biotar lens. Just as I was going out of the train I got a phone call that made me forget to pick my rucksack from the luggage rack. I'm still chasing the lost property office, but the chances that I recover it seem slim...
Pentax K-X, Carl Zeiss Jena 1Q Biotar 2/58 mm (10 Blades)

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