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[OM] Re: the "one over focal-length guideline"

Subject: [OM] Re: the "one over focal-length guideline"
From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxx>
Date: Wed, 26 Oct 2005 22:51:10 -0400
Andrew Dacey wrote:
> On 10/26/05, Robert Swier <robert.swier@xxxxxxxxx> wrote:
> 
> 
>> Here's the question: What's the equivalent rule for the E-1? (Or more
>>generally, for any system with a frame size different from 35mm).
>> My feeling is that you need to convert to the 35mm equivalent in order for
>>the rule to still work. That is, if you get camera shake when shooting a
>>100mm Zuiko at 1/60, then you'd also get shake when shooting the 50mm
>>Digital Zuiko at 1/60.
>> That's right, isn't it?
> 
> 
> I'm going to guess no. Imagine that you took a 35mm shot that was shot
> with a 50mm lens and cropped it down to the field of view you'd get
> with a 100mm lens; that's not going to introduce any more shake.
> That's essentially what you're doing with the 4/3 system.
> 
> The only situation I could see it being an issue would be that you're
> essentially blowing up that crop to a larger size (so that the crop
> would be the same size as the original shot) so small motion that
> wasn't noticeable in the full shot might show up now.
-----------------------------------------------------------------

Winsor has it right.  You do have to account for the multiplier to apply 
the guideline.  You're correct in that you're not producing anymore 
shake but your "only situtation that's an issue" is an issue 100% of the 
time.  If you're going to print a 4/3 image to the same size as you 
would with 35mm then you're magnifying the image by twice as much and 
emphasizing the shake by a factor of 2.  Compensate by multiplying the 
focal length in use by 2 to get back to the 35mm guideline.

Now, whether the original guideline was of any real use is another question.

Chuck Norcutt


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