[MF3D.FORUM:1137] Re: Intro, Deviation and Viewers for a 43mm taking lens

["Dr. George A. Themelis" <DrT-3d@xxxxxxx>]

>>M = 250mm/FL

>It seems that this
>formula holds true when the image has an apparent distance of Infinity, but
>if the image appears to be at a distance of 10 inches, one is supposed to
>increase the calculated magnification by a value of 1. 

Correct.  I always focus the viewer for apparent distance
at infinity because this is the most comfortable viewing
arrangement.  The eye muscles are relaxed.  That's why
I omitted the "+1" factor.

>   Magnification = (10 * x^-1) + (250mm / viewer FL)  
>
>again, where x is the apparent distance to the image.

>OK, I have jumped from the frying pan where I didn't know how to calcuate
>Magnification to the frying pan where I don't know how to measure the
>"apparent distance to the image."   Joy!

That depends on how you focus the viewer.  Try increasing the
distance between the lenses and the slide as far as you can
go but still see things clearly.  Now you have focused the
viewer at infinity.  Now, reverse this process.  Reduce
the distance between the lenses and the slide.  You will
start accommodating your eyes in order to see a clear image.
A LARGER CLEAR IMAGE.

When you cannot see a clear image any more then you have
focused the viewer at your closest accommodation distance.
This distance depends on your age.  If you are as old as I
think you are :) then it should be no shorter than 10 inches.
So you've got your +1 factor.  But my 8 year old son can 
focus his eyes at the tip of his nose.  For him this factor
is even larger!  BOY, DOES HE SEE A LARGE IMAGE THROUGH
THE STEREO VIEWER!!!!

Hope this helps your calculations.

George