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W.O. BVs. - shorter poles for truss scope.

Started by mpanucci, 11/05/2005 01:53PM
Posted 11/05/2005 01:53PM Opening Post

I have recently delt with the expected problem of reaching focus on a fast newt. I own a 16" f/4.6 truss newt. I could not reach focus with or without the provided OCS.
Actually if I could reach focus with the OCS,,,, I still would not reserve myself to high mag observing.

Following the Denk website and some other review web sites, an option to truss scope owners is to shorten the poles. Well,,, I entertained the idea and made up a set of poles that were 4 inches shorter. It worked great!

I can observe at ~ 90X with a FOV of ~ 0.7'. Nice! I highly recommend the modification if you like wide field observing.

I carry my 2 sets of poles in a box. I obviously decide if the night will be a Ocular Night or Binoviewer night. I dont plan to change poles during the night.

BTW I figure I am losing < 1 inch of aperture. No big deal.

My ray trace situation is very forgiving on my scope. I use 3.5" secondary. When using the shorter poles,,if I rack the focuser in all the way and look down without an EP in place,,,I can "just see" the outer perimeter of the primary mirror.

Michael Panucci
My Astro MSN Web Pages :

Posted 11/05/2005 03:40PM | Edited 11/05/2005 03:44PM #1
Mike is this view looking into the focuser without an eyepiece in it or is this the amount of mirror you see with the binoviewer in the focuser without an eyepiece? The latter condition more accurately represents the amount of vignetting
or under illumination of the field that may be occuring.
If an OCA is used the entire cone of light will be intercepted by the objective lens of the OCA due where it is placed in the optical path. Also if high power for planetary observing is desired you will probably achieve better results with a barlow in front of the binoviewer rather than using eps significantly shorter in FL than 10mm
for high power.