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[OM] Re: More Experimentation

Subject: [OM] Re: More Experimentation
From: Moose <olymoose@xxxxxxxxx>
Date: Sat, 02 Aug 2008 01:03:21 -0700
Jim Nichols wrote:
> Moose,
>
> First off, I'm cheap.  I use what I have at hand, or, can obtain cheaply.  
As was I, but what I have at hand, not what you have at hand.  :-)   But 
for a reversed lens, it would be a Zuiko, and the Oly bellows provides a 
means to use, and focus, a reversed lens while retaining auto-aperture 
operation with double cable release.
> I have a 50/1.4 Takumar, but have it dedicated to my film SLR.  
I am somewhat more flexible. The Tamron 90/2.5 macro is in the copystand 
kit along with a 50/3.5 macro, but I am free to use it for other purposes.
> That left the 55/1.8 and 2x extender free to play with.
>
> I assume that, to reverse the lens, the adapter would have to attach to the 
> filter threads.
That's correct, except for more complex ones, like the bellows. The Oly 
bellows slides and clamps onto the outer front of the lens, 49mm Zuikos 
by default, 55mm with an adapter.

I believe Scott said you can only focus by moving the camera when using 
a reversed lens. That is true of AF designs without the option of 
mechanical manual focus, like the ones he used. With MF lenses like your 
Takumar, the focusing helicoid works fine reversed. About the easiest 
way to use it with a simple reverse adapter is to set it in the middle 
of its range, get the camera where the image is close to focus, then use 
the focusing ring for fine focus.

Setting the aperture also depends on the age and design of the lens. 
Early Pentax screw mount lenses were preset. Later ones, which you 
probably have, require a pin on the back to be pressed to stop down the 
diaphragm. If you tape or otherwise keep the pin pushed in, the aperture 
ring then works to adjust the diaphram when reversed.
> I really don't understand what this would do for me, unless it would give me 
> a different distance to the sensor which could be used beneficially.
>   
Chuck has already explained some of the optical reasons. Scott got some 
good central results with a reversed zoom. You can expect better results 
over the whole frame with a reversed prime lens of basically symmetrical 
design, like most standard 50mmish lenses for 35mm film, which are all 
variations of the symmetrical double-gauss design.

Moose

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