Re: ATM Barlow + Extension Tube = ?

[Andy Saulietis <iss@pvtnetworks.net>]

L Sayre writes,

>I have a 2" 1.5x barlow which has its achromat lens elements recessed
>~3.8" in from the barlows eyepiece shoulder.  If I insert my 1.5"
>extension tube into the barlow, and my eyepiece into the extension tube,
>what effective x will the barlow deliver.  Alternately, how much
>extension tube length would be required to up the magnification factor
>of this barlow from 1.5x to 2x, 2.5x, and 3x.
>
>Are there simple formulas for calculating this?

Yes, but you need to know the focal length of the
Barlow lens.  This can be reverse engineered by
measuring the magnification at 2 known distances from
the objective, and solving for the fl in the formula for magnification.
(which I don't have handy here but it's in the old ATM 1,2,or 3 book.

Magnification isdefined as image size with barlow divided by
image size without.


Andy Saulietis
ISS Enterprises
39 Silver Fox Trail
Mayhill NM 88339
505-687-3067 voice
505-687-3021 fax, call voice or e-mail to set up
e-mail: iss@pvtnetworks.net