Hi Tim, Andrew, and all,
From: Tim Hughes <timhughes@xxxxxxxx>
>Sounds like maybe the "Bowen" adapter has to have a weak glass element,
because >either the mounting lugs on the flange interfere and/or because the
throat >diameters are similar and so are incompatible.
Most likely.
>Adding the lens allows the flanges/throats to be separated.
Yes... and adds two side effects:
-Decreases picture quality :-(
-Acts as a mild teleconverter
>I could not find any bowers alpha-OM adapters listed on ebay, although
there are >lots of adapters for other vendor's lenses to alpha.
I don't there are so many... M42 thread (1mm longer register _and_
relatively shallow, so free from the hassle of bayonet lugs) and the older
Minolta MD mount... but the latter needs a correction lens :-(
>This means you could kludge an adapter using a weak lens adapter and
machining >it down and attaching an OM flange if the bowen adapter is
unavailable.
>
>The pros of doing that would be a 25Mpixel OM lens compatible, FF camera
*with IS >*!
Yes, but the real point (to me) of having a FF digital body _with adapters_
is to use the full angle of view from the manual wide-angle lenses -- and
there are very good ones on the OM system. But if the adapter is also a
teleconverter... there's no point! It would be much better to use a cropped
sensor without any glass on it.
>I did some more searching and found "Domestic_platapus" on ebay, seems to
have >sold an adapter for 7000/9000-O/M not too long back.
But surely with a correcting lens -- no good :-(
>and it might still not accommodate the wide angle OM's with the protruding
lens >guard at rear.
Yes.
>Using OM lenses on Leica/Minolta CL rangefinder cameras.
>http://www.rangefinderforum.com/forums/showthread.php?t=76055
Interesting link! Thanks a lot!
On 30/09/2009, at 10:03 AM, usher99@xxxxxxx wrote:
> Something seems askew with the adapter businness. The registration
> distance for OM is 46mm and the Sony/Minolta AF is 44.5 leaving only
> 1.5mm. As mentioned the bayonet release takes up a bunch of space.
From: Andrew Fildes <afildes@xxxxxxxxxxxxx>
>That's enough. The difference between Leica screw mount and Leica M
>mount is just 1mm - and deliberately so. That's how they designed it
>when they changed over in 1954! That's why the M bayonet adapters are
>skinny rings.
Yeah, but the M mount was designed specifically to be adaptable for the
older Leica Thread Mount lenses -- the investment should keep protected! A
39mm screw mount is easy to adapt because it's narrower than the M bayonet
_and_ has no bayonet lugs etc.
A similar case is the Pentax K-mount, designed to be compatible with the
42mm thread mount -- EXACTLY with the same register (45.46mm). AFAIK, the
K-mount is a bit wider than the OM, so there's no problem to place the K-M42
adapter _inside_ the K bayonet, using its flange for the adapted lens.
Usually supplied with a tool for removal.
From: Tim Hughes <timhughes@xxxxxxxx>
>As discussed before , it may depend more on whether the bayonet outer
diameter >on the OM flange interferes with the throat diameter of the alpha
body. The flange >websites never give the throat diameter needed to know the
fit! The outer diameter >of the OM bayonet is 47mm. So the inner diameter of
the alpha has to be say ~ >49mm, not to interfere and to provide space for
an OM bayonet
I don't know the exact dimensions, but measuring on a web picture of the
A350 (130.8 mm width) it looks like having an _outer_ diameter of ~51mm. But
this mount has a lot of protruding, rotating things inside, so the clear
_inner_ diameter seems not much more than ~42mm... Sad news, I'm afraid.
>Looking at this website :
>http://www.gadgetinfinity.com/product.php?productid=17019
<snip>
>but it seems there is not quite enough space to make an actual locking OM
bayonet >mount inside.
The same website has some Nikon-to-Alpha adapters -- all with glass. And the
F-mount has 0.5 mm _more_ register and about 45mm outer diameter, thus
"easier" than the OM bayonet, but no way...
>We need somebody with access to an alpha to measure the throat diameter to
>confirm this guestimate, but it does not look too promising
I have scheduled on Tuesday a visit to a friend who does have an Alpha
camera! I'll check it out, but I don't think will make things easier,
anyway.
>Here is website which shows how to remove the normal flange (in their case
a >minolta old lens) and just uses the M42 to alpha adapter with a spacer.
>This would be difficult with OM as the stop down mechanism of lens would be
>removed along with the old OM flange, apart from being sacriligious!
>
>http://www.flickr.com/photos/arkku/1266937278/in/set-72157600018767343/
A word of caution about flange distance... some cheap adapters do focus a
bit _beyond_ infinity, because they're thinner than expected. Although this
doesn't seem a big issue at first glance (the opposite would!), there is a
real danger: lenses with correction mechanisms at close range. Since the
distance set on the focusing ring no longer matches the actual distance to
the subject, the optics are no longer optimized and performance _will_
suffer. Been there, done that.
Interesting link, though.
Cheers,
--
Carlos J. Santisteban Salinas
IES Turaniana (Roquetas de Mar, Almeria)
<http://cjss.sytes.net/>
--
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