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[OM] Re: Focus stacking calculations

Subject: [OM] Re: Focus stacking calculations
From: "Wayne Harridge" <wayneharridge@xxxxxxxxxxxxxxx>
Date: Fri, 2 May 2008 20:58:54 +1000
Thanks for that Moose, not really intuitive so doing the maths was a
sensible step.

...Wayne


> 
> Wayne Harridge wrote:
> >
> > Yeah, probably the best approach is to use a longer lens on 
> a bellows 
> > and refocus on different parts of the subject adjusting the 
> rear bellows standard while maintaining the distance from the 
> lens to subject fixed (e.g. The Zuiko 135/4.5 macro on the OM 
> Auto Bellows).
> >   
> I've added the rear bellows standard adjustment alternative 
> to the table:
> 
> Calculated for a 50mm lens, here are the changes in magnification 
> resulting from adding about one inch, 25mm, to the focal distance:
> 
>                               Move Camera     Refocus         
>       Adj. 
> Bellows
> Repro    Magni-      Image    -----------   ------------   Change   
> ------------   Change
> Ratio    fication    Size     Size   %chg.  Size    %chg.   Ratio   
> Size    %chg.   Ratio
> 1:10      0.10         2.5     2.4    -4%    2.2    -13%     3.0     
> 2.4    -05%     1.1
> 1:5       0.20         5.0     4.6    -8%    3.8    -24%     
> 3.1     4.5 
>    -09%     1.2
> 1:2       0.50        12.5    10.7   -14%    6.7    -46%     
> 3.2    10.0 
>    -20%     1.4
> 1:1       1.00        25.0    20.0   -20%    7.8    -69%     
> 3.4    16.7 
>    -33%     1.7
> 
> Moving the entire camera without changing the focus is still the best 
> alternative. Fortunately, it's also far the easiest, as it doesn't 
> involve the refocusing required by the other two.
> -------------------------------------------------
> And I've done the calculations for a 135mm lens.
> 
> Calculated for a 135mm lens, here are the changes in magnification 
> resulting from adding about one inch, 25mm, to the focal distance:
> 
>                               Move Camera     Refocus         
>       Adj. 
> Bellows
> Repro    Magni-      Image    -----------   ------------   Change   
> ------------   Change
> Ratio    fication    Size     Size   %chg.  Size    %chg.   Ratio   
> Size    %chg.   Ratio
> 1:10      0.10         2.5     2.5    -2%    2.2    -11%     6.5     
> 2.5    -02%     1.1
> 1:5       0.20         5.0     4.9    -3%    4.0    -20%     6.6     
> 4.8    -04%     1.2
> 1:2       0.50        12.5    11.8    -6%    7.4    -41%     7.1     
> 11.4   -08%     1.5
> 1:1       1.00        25.0    22.9    -8%    8.8    -65%     7.6     
> 21.1   -16%     1.8
> 
> The longer lens does indeed make for less magnification change.
> -------------------------------------------------
> This is all in a spreadsheet, so alternative focal lengths and focal 
> plane changes may be calculated quickly. Not instantly, as there are 
> four values that have to be calculated by goal seeking iteration.
> 
> A. Calculating Moose
> 
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