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

Subject: Re: [OM] Focus Accuracy Test - Oh what misery we bring uponourselves
From: "C.H.Ling" <ch_photo@xxxxxxxxxxxxx>
Date: Mon, 16 Aug 2010 22:53:48 +0800
I understand very well what you mean, I have recomended this focus method 
many times here (with focusing screen on the matte area). But I don't think 
it works well here with the OM 24mm lens to differentiate object between 5 
and 6 meters, the travel distance is just too small (left and right 0.5mm or 
even less). This may be possible with other lenses like the Tamron SP 24-48 
I had as the lens has a much longer focusing scale.

C.H.Ling

----- Original Message ----- 
From: "Ken Norton" <ken@xxxxxxxxxxx>

>> I'm not sure if 5D II has poorer liveview than L1 but based on the DOF
>> calculator:
>>
>> http://www.dofmaster.com/dofjs.html
>>
>> If I set CoC to 0.006mm (35mm/5616pixel), object distance 5.5 meter, the 
>> DoF
>> is 4.74m to 6.56m. It indicates one cannot differentiate the focus 
>> between 5
>> and 6 meter, or I have missed something?
>
>
> Basically, the rule of thumb is that when you select a single point
> and attempt to focus in to that point from one direction you correct
> in that it is difficult to identify one focus point from another as
> they both fall within the margin of error (DoF). But if you rock back
> and forth you'll establish the points of known defocus and then be
> able to adjust to a midpoint. Somehow I managed to successfully do
> this to a greater granularity than would normally be possible.
>
> AG

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