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Re: [OM] 100 shootout

Subject: Re: [OM] 100 shootout
From: "Jim Nichols" <jhnichols@xxxxxxxxxxxxx>
Date: Fri, 30 Sep 2011 19:19:43 -0500
Have you thought about sub-contracting to Moose, with his super eyesight?

Jim Nichols
Tullahoma, TN USA
----- Original Message ----- 
From: <usher99@xxxxxxx>
To: <olympus@xxxxxxxxxxxxxxxxx>
Sent: Friday, September 30, 2011 6:57 PM
Subject: [OM] 100 shootout


>I agree with AG AND Dr. Focus.  Focusing accuracy is a key parameter 
> and need to meticulously exclude
> focusing differences to explain any findings.
> 
>   I was home yesterday and tried another focus stack (perhaps a futile 
> attempt) (with gross calc dof in hand)
> There was a pesky breeze and the light was changing and getting 8 good 
> images was not easy (probably actually not accomplished) .  I think 
> with mag (10X)  LV
> one can discern some differences within the calculated dof.
> 
>  Bracketing   the mid point of the proximal and distal dof limits as 
> well as multiple repetitions should
> minimize the effect of this variable.
> 
> Dawid is of course correct for an ideal lens, though with any complex 
> lens subtle changes in the dof would be expected.
> I have trouble differentiating the magnitude from the "rendering." of 
> the defocused area though I understand what he is getting  at.   If it 
> looks sharper it may as well be called sharper as it is a visual 
> endpoint.
> Perception is reality in this realm for all practical purposes , IMO.  
> Then one must also be careful where in the frame the focus point is 
> because of
> possible field curvature.  There also may be unknown unknowns, but I 
> don't know.
> 
> Even thinking about complex zooms with asymmetrical elements makes my 
> head hurt.
> 
> Undoubtedly Zeiss has full wave solutions for most  their  lenses and 
> could just calculate this stuff despite the somewhat arbitrary nature 
> of determining the Coc.
> That some of these effects are not trivial is born out by the Zeiss 
> focus shift link.
> 
> If I like this thread does that mean there is a problem,  Mike
> 
> 
> 
> 
> 
> I'm going to AGAIN do the tape-measure test. Not to prove anything to
> you, but to answer this lurking question in my own mind as to why the
> two lenses aren't focusing the same even though they appear to be
> focusing at the same point. The Zeiss article definitely points to
> this as being either a nodal-point difference or a focus shift due to
> aperture adjustment. The Zeiss article also addresses the cone
> differences at identical apertures from lenses of different maximum
> apertures.
> 
> In the world of assymetrical lens elements, all bets are off.
> 
> AG
> 
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>

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