Re: [OM] New? fast prime for MFT

Subject: Re: [OM] New? fast prime for MFT
From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxxxxxxx>
Date: Wed, 03 Mar 2010 17:54:12 -0500
2 stops wider is exactly correct for a 2X crop factor as long as you 
also apply a 2X factor to the focal length and the CoC.  20mm at f/1.7 
on 4/3 gives exactly the same DOF as 40mm at f/3.4.

Dr. Focus

usher99@xxxxxxx wrote:
> Yes, the 20mm f1.7 is a nice one indeed but the selective focus crowd 
> would like a stop or more faster for more flexible dof control.
> DOF equivalence is about F 3.4 on FF.  Not as impressive when viewed 
>  from that  perspective.  Dr. Focus and  AG have calculated the exact  
> dof difference, but 2 stops is close enough for gov't work.
> Mike
>> 0.95 is pretty spectacular - the fastest available by anyone.
>> I'm more concerned by the rather lousy looking bokeh. I think this is
>> one for movie use where the criteria for sharpness and out-of-focus
>> rendition are less important than some other characteristics, such as
>> DOF control.
>> Andrew Fildes
>> afildes@xxxxxxxxxxxxx
>> On 03/03/2010, at 5:10 PM, Nathan Wajsman wrote:
>>> But there is already a fast prime, the excellent 1.7/20mm. Not
>>> Noctilux fast, granted, but 1.7 is still pretty fast.
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