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Re: [OM] Magnification vs focal length, was: Moose Arrives In Maine - Lo

Subject: Re: [OM] Magnification vs focal length, was: Moose Arrives In Maine - Locals Amazed
From: Bob Whitmire <bwhitmire@xxxxxxxxxxxxxx>
Date: Tue, 24 Sep 2013 08:41:45 -0400
Stop it! This makes my head hurt, and also makes me feel inadequate. I don't 
need that! <g>

--Bob Whitmire
Registered Neanderthal

On Sep 23, 2013, at 8:18 PM, usher99@xxxxxxx wrote:

>>> I think I get it now (though I don't understand your 
> equation/formula: 1/f
>>>> by (1+M)**2).
> 
> To be more clear: Shutter speed to have 40-60% chance of sharp or 
> slight blur =1/ ((focal length)*(1+M)**2)
> (multiple qualifications apply)
> 
> One doesn't really have to measure blur, angular velocity for proof of 
> principle just displacment of the image,
> IMO. How about take a 50mm and 100mm prime (macro lenses or zooms are 
> more complicated as FL may change at close focus) and use extension 
> only to get 1:2 mag or so--must be the same!!. The 100mm lens will have 
> more working distance of course. Might be easiest to be sure the tripod 
> head is level and just move at 5 deg (you pick) in left/rt plane and 
> assess movement of the target image (target with rulers up down/left 
> right would be great--must be available to download somewhere). At same 
> mag, the target image would move much more with teh 100mm lens thus the 
> same angular velocity of shake would result in more blur  which turns 
> out to be proportional ot the focal length.
> Perhaps a proper thought experiment is adequate. Rushing to get home 
> and perhaps should think more about this b4 posting but wanted to 
> respond. I haven't cleared this with Dr. Shake yet. Not sure why this 
> isn't more obviously  intuitatively correct. Increase mag will result 
> in movement across more sensor pixels and thus more blur so perhaps 
> that is obvious as well as increased angular velocity of shake leading 
> to more blur.
> I am not an engineer or mathematician nor play one on TV though.

-- 
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