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Re: [OM] Mind Bender (intermediate focal length?)

Subject: Re: [OM] Mind Bender (intermediate focal length?)
From: Joe Gwinn <joegwinn@xxxxxxxxx>
Date: Thu, 28 Nov 2002 10:54:29 -0500
Comments below.

At 8:57 AM +0000 11/28/02, olympus-digest wrote:
>Date: Wed, 27 Nov 2002 18:33:30 -0800
>From: dreammoose <dreammoose@xxxxxxxxx>
>Subject: Re: [OM] Mind Bender  (intermediate focal length?)
>
>In the focal length series I calculated based on FOV, I used the 
>theoretical FOV, calculated using simply focal length and film width.

This approach does have the advantage of largely eliminating the effects of 
lens design.

>Moose
>
>Joe Gwinn wrote:
>
> >The problem is that field of view varies from lens design to lens design, 
> >even if the focal length is the same, so using FOV values to determine 
> >something like "intermediate" is only approximate.  
> >

I was thinking also of the lenses used on view cameras, where the field of view 
(that is, image circle) vastly exceeds the film size.  Ditto, shift lenses for 
35mm.  So, I was looking for an algorithm that included only data that was true 
of all lenses, regardless of design, which leaves only focal length.

Anyway, we have two answers, 141.4mm (~140mm) and 135mm.  I don't think it much 
matters which answer one uses:

140/100= 1.400
200/140= 1.429

1.429/1.400= 1.020


135/100= 1.350
200/135= 1.481

1.481/1.350= 1.097

And of course, 140/135= 1.037

So, we are within 40f each other, far too small a difference to be 
photographically significant.  At this point, the question will devolve to a 
question of optical quality of the actual lenses in question.  We can even 
debate relative bokeh, if we have the energy.


Joe Gwinn


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