Re: [OM] OM wides (21/2, et al)

[C.H.Ling]

The errors happen in focusing can be much larger than you have expected 
since you are using the focusing screen not the lens scale, you can't unless 
the lens has VERY accurate and fine enough meter scale and the film to lens 
mount distance has to be very accurate too.

Even with digital gears, focus can be critical not to mention the film age. 
(with digital you can make much more test shots and get immediate feedback).

http://www.slrgear.com/articles/focus/focus.htm

BTW, when talking about lens variance, it could happen on the wide lenses as 
I have seen some fixed wide angle lenses and wide zooms with uneven 
performance even on left and right sides not to mention variations between 
different lenses. On the other hand I have never seen the same happen on 
tele lenses. Ok, I'm talking about the manual focus lenses, AF lenses can be 
much worse.

C.H.Ling

----- Original Message ----- 
From: "Chuck Norcutt" <chucknorcutt@xxxxxxxxxxxxxxxx>

> Good point but focusing error should hopefully be accommodated within
> the DoF since he used a flat target at 1:40 magnification.  That's 2.1
> meters for a 50mm.  Even at f/1.4 the DoF on either side of the target
> ranges from about 77mm in front to 84mm behind.  By f/16 it's more than
> 1/2 meter in front to more than 1-1/2 meters behind.  Perhaps all part
> of the warning not to compare except across a full letter grade.
>
> Chuck Norcutt
>
>
> Wayne Harridge wrote:

>>>
>>
>> ...and what about focussing accuracy ?
>>
>> ...Wayne
>>

-- 
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