Re: objectives/occulars for stereo zoom

Kevin Cunningham wrote:

>
> "George Pontis" <gpontis@xxxxxxxxxxx> wrote in message
> news:43cbbb2b$0$96010$742ec2ed@xxxxxxxxxxxxxxxxx
> > Here is a rank amateur question about choosing occulars and
> > objectives for a stereo zoom microscope. In essence: what is the
> > difference between 10X occulars paired with a 0.5X objective, and
> > 5X occulars paired with a 1.0X objective ? I understand that
> > working distance is greater with the lower powered objectives, but
> > what else ?
> >
> > ...
> >
> > --
> Good question! The answer is two fold and you already guessed one.
> Higher mag objectives whether stereo or compound usually have higher
> numerical aperatures (NA), that means more resolution. In practice,
> this is the one you got right 10X eyepieces have more field number
> than other eyepieces since for every 10X eyepiece about .0000001
> other eyepieces are built. Its better in practice to to change the
> front lens than the eyepiece because other eyepieces don't have the
> same field diameter (field of view).
>

Bad assumption on my part that "FN" scaled inversely with eyepiece
magnification. I looked at the numbers for Meiji 10X with 1X objective
and FN is 23. The 5X eyepiece with same objective is only 26. That
doesn't seem fair.

The "downside" to having a collection of objective lenses is the cost,
at least when it comes to the Leica and Nikon. The Meiji (with
Greenough optics) has a set of auxilliary lenses that are not
expensive. One option is the 0.5X barlow. In practice it seems to work
pretty well. Can I assume that resolution (or something else) is lost
compared to the plain objective ? Does depth of field scale inversely
with magnification when using such an aux lens ?

Thanks again,

George

--

.

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