[MF3D.FORUM:511] Re: viewer lenses vs. magnification?

[Greg Erker <erker@xxxxxxxxxxxxxx>]

>     I have 78mm viewing lenses in my Saturn viewer.  How does this figure
>relate to magnification?  If normal is about 45mm, then wouldn't this only
>be about 2x magnification?   I seem to remember heraing 3 or 4x though?
>
>      I plan to divide a circle of confusion of .3mm by this magnification
>value to enter into my DOF tables.  I know this is how it works in 2D, I
>would assume this is correct for 3d also, right?
>
>Bill G

  There are two common equations for calculating
magnification. If you use the lens to make the
slide appear at infinity focus then the mag
is 250/FL which for your lenses is 3.2x

  If you move the lenses in closer you get
more magnification and the image appears to
be nearer than infinity. For loupes they
usually use 1+250/FL for mag which gives
4.2x for your 78's.  The formula assumes
the image appears at 10" (250mm) away.
If you focus for 20 or 40" away then the
mag formula would be 0.5+250/FL or 0.25+250/FL.

  The DOF numbers I gave earlier are
based on 0.06mm COC by the way.

Greg E.