Re: ATM fast aperture and bino viewers

[Andy Saulietis <iss@pvtnetworks.net>]

Fabio writes,

>I own a BW bino viewer (it should be identical to the Lumicon unit). It has
>a 22 mm clear aperture and a 120 mm focus in travel. Given these it should
>be not possible to accomodate a faster beam than about f/5.45. Right?
>I'm building a 20" dob. If I choose the mirror to be an f/4 I will loose
>4/5.45 of the aperture, i.e. at the center of the eyepiece I'll have the
>light coming from a 14" aperture. If I choose a f/5 mirror the reduction is
>to 18".
>Having not heard of this problem before pheraps I'm missing someting.
>I know that using a barlow will answer to the problem, but not completly:
>I'll be stick to very high magnifications.
>What do you advise to do?

You could use a Barlow lens between the scope and bino viewer.
This will increase the available 'in' travel & increase the f#
by the magnification ratio. Real field is less but you can use
all of the aperture. 1.5x would be sufficient.



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