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Re: [OM] Changing lens mount

Subject: Re: [OM] Changing lens mount
From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxxxxxxx>
Date: Sun, 05 Dec 2010 18:00:10 -0500
In John Shaw's book "Close-ups in Nature" he spends a couple of pages 
discussing macro shot with teleconverters.  This is a useful read since 
it discusses four different arrangements with teleconverters and 
extension tubes all of which (although producing exactly the same size 
image) all produce different effective focal lengths, different working 
distances and different amounts of light lost.

But in the end he says the best way to use a TC for macro is to use a 
low powered one and... only when you must.  That said, he also says that 
a TC can often show better than expected performance when doing macro. 
At least in comparison to typical results when used in non-macro mode 
just to increase focal length.  He believes the reason is simply small 
apertures, tripods and careful technique when shooting macro.  Compared 
to typically wide or near wide open shooting as a telephoto to 
counteract the loss of light and also image shake from the longer focal 
length typically used without a tripod.

I intuitively thought that a wide angle lens should be much less 
susceptible than a telephoto to adapter parallelism errors and intended 
to do some calculations to prove myself right or wrong.  But my patience 
with doing depth of focus calculations this morning eventually grew 
shorter than my curiosity.  :-)

Chuck Norcutt


On 12/5/2010 4:33 PM, usher99@xxxxxxx wrote:
> I'm still having difficulty accepting this except in the case of
> extraordinarily badly built adapters.
>
>
> Thanks for the depth of focus analysis.  Some poorly made adapters were
> reported to be visibly lopsided
> with others causing difficulty with lens mounting or dismounting---some
> terribly stuck.  The tilting issue Jeff
> noted is especially a problem with heavier lenses---I was not aware
> that this may be difficult to initially  detect.  Leitax offers screw
> on adapters
> to the native lens mounts where a standard free mounting adapter would
> usually do--this eliminates the tilting issue..  He provides longer
> screws and the
> procedure is reversible.  It costs no more than some higher quality
> adapters.
> I am not exactly sure why there is more trouble with WA's though no one
> spoke up on FM to contradict that.  One issue  thin adapters and WA's
> is the rear
> element may hit the mirror where clearance is tight.  I thought some
> lens designs may just be more sensitive to having the registration
> distance off---
> I recall an e-mail exchange with a Tamron  tech  (don't remember which
> lens)  where he said one would get better performance using a matched
> TC than
> adding extension.
>
> Life is too short for mediocre wine or poorly made adapters for my
> Zuikos, much as I like a deal,   Mike
-- 
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