Actually, the reference chart was M42 x 4.5 tpi, which is mixing
metric and ASA. Somethings not right there. It then goes on to
describe the inch equiv. as 1.6535 x 5.64 inches.
Your Pentax camera lens SM is 42 mm x 1 mm, as Paul said. I measured.
On Apr 1, 2009, at 19:44 , JC OConnell wrote:
The tool page he reference was M42-5 not M42-1
-----Original Message-----
From: pdml-boun...@pdml.net [mailto:pdml-boun...@pdml.net] On Behalf
Of
Paul Ewins
Sent: Wednesday, April 01, 2009 9:23 PM
To: Pentax-Discuss Mail List
Subject: Re: do any m42 adapters do auto stopdown?
M42x1 would be the same regardless of whether it is photographic
equipment or heavy machinery since it describes a thread with a 42mm
diameter and a 1mm pitch. There is no guarantee that something (other
than camera equipment) described just as M42 wouldn't be M42 x 0.75 or
M42 x 1.25, but I would bet that any M42 lens would be M42x1.
Accrording to wikipedia Leica thread mount is M39 x 26tpi (whitworth)
which works out at M39x.977. Apparently early Zorki and early Canon RF
cameras used M39x1.
It gets really murky in the world of large format lenses and shutters
where some of the metric sizes are very close to imperial sizes and
you need to measure very carefully to work out exactly what you have.
Prior to WWII there weren't any real standards and lots of oddball
sizes exist.
Paul
On a related note, is what we call m42 the same as what machinists
call M42?
http://www.besly.com/catl/catl4124ps.htm#M42
Yes, I think so. Leica screw mount is M39.
Joseph McAllister
pentax...@mac.com
http://gallery.me.com/jomac
http://web.me.com/jomac/show.me/Blog/Blog.html
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