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Re: [OM] Focus Accuracy Test - Oh what misery we bring upon ourselves

Subject: Re: [OM] Focus Accuracy Test - Oh what misery we bring upon ourselves
From: Moose <olymoose@xxxxxxxxx>
Date: Sat, 14 Aug 2010 21:47:13 -0700
  On 8/14/2010 4:51 PM, Chuck Norcutt wrote:
> I've read your note a couple of times and reviewed the images several times 
> and I still don't see what you seem to see.  To me all the test images show 
> as equally sharp across the depth of the test area.  I just can't tell a 
> difference.

Ah well, I still see it, but maybe it's a hallucination. For this sort of test, 
I use a vertical target that presents a 
large area all in the desired distance plane with both text and graphic on it, 
to give a bigger area to view and 
different things to view. Product boxes are excellent targets. When I was 
testing the first version of the Tammy VC 
lens, I used part of a bird feeder box.

> But your comments on background details caused me to look where I hadn't 
> before.  Recall that the original impetus for this test was that the ZD Zoom 
> supposedly showed more in-focus background detail and thus "greater" DoF.

Sure, I remember. But I only looked at these test images for the purpose for 
which they were shot. I don't like 
conflating two different tests.

> OK, look at the brick wall in the background.  The brick wall is decidedly 
> less sharp than the OM Z
> even though it's operating at f/3.2 instead of f/2.8.  That may be edge of 
> field resolution problems but the same would have been the case in the 
> original field/tree photo.

I honestly don't think the DOF issue can be meaningfully tested except near the 
center of the field. There are just too 
many other differences in aberrations that could muddy the results. These are 
VERY different lens designs.

Remember the considerable center/edge differences between Zuiko and Zeiss 18mm 
lenses in Mike Hatam's tests? And those 
are lenses with much more similar designs than these two.

> Anybody care to join in?  Is it Moose's eagle eye that sees a difference I 
> don't?  I've even tried blowing it up a bit beyond what is supposed to be 
> 1:1. I still can't see anything significant.

If you simply enlarged it on the screen in PS, you aren't really helping, as 
the algorithms used for screen viewing 
aren't all that precise.

Moose
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