Re: [photo-3d] Re: Loupe question, magnifiers, confusion

["Don Lopp" <dlopp@xxxxxxxxxxxxxxx>]

as reguards to 250/Fl as that is what were told years ago in school. I think
the 250/Fl. plus one was foisted on us by merchandisers such as Edmund
Scientific [ Edmund Salvage ] and others trying to make their magnifiers
look better by comparison power wise- like counting # jewels in a watch or
the # transistors in a radio when the # does not neccesarily indicate the
quality of the product. I think the important thing is to put your eyes in a
state of relaxation. Maybe Dr T can explain why photographic lenses should
be focused at infinity  and not at closer distances-there is only one
infinity where as closer distances are plus or minus depending on the amount
of depth of focus or depth of field allowed. Don.
----- Original Message -----
From: "Dr. George A. Themelis" <drt-3d@xxxxxxx>
To: <photo-3d@xxxxxxxxxxx>
Sent: Saturday, November 04, 2000 11:31 PM
Subject: Re: [photo-3d] Re: Loupe question, magnifiers, confusion


> I think there is a mistake in your analysis:
>
> >   Magnification = 250mm/FL + (10 * x**-1)
> >
> >If we could focus on an object at 0 inches distance, the formula
> >would describe the intrinsic magnfication offered by the lens itself:
> >
> >   Magnification = 250/FL + (10 * 0**-1)
> >
> >   Magnification = 250/FL + 0
>
> This is incorrect.  If x = 0 then x**-1 (essentially 1/x) is
> infinity, not zero.  Zero is achieved when x = infinity
> or when the we focus at infinity, which happens when
> the eye muscles relax.
>
> In presenting this general formula you are assuming that the
> user WANTS to achieve the closest focusing distance.
> This usually strains the eyes and it is not necessarily
> desirable.
>
> Personally, I prefer to have my eye muscles relaxed when
> I view stereo slides (or even when using microscopes or
> other optical instruments), therefore I focus the viewer
> for infinity viewing, which gives:
>
> Magnification = 250mm/FL
>
> George Themelis
>
>
>
>
>