Re: Request for opinions on telescope parts

From: Howard Lester (heylester_at_dakotacom.net)
Date: 03/13/05 

Date: Sun, 13 Mar 2005 09:23:07 -0700

"Jan Owen" wrote

> Personally, I'd go with the 1.52 secondary. It's a good compromise for
> excellent images on all the objects you mention. You could go up or down,
> if you wanted to specifically explore the planets, or just do DSO's, but
> for all-around performance, the 1.52" is hard to beat...
>
> I like your choices otherwise, except, perhaps, the UO primary cell. It
> will be OK (and they also have a new one for which I have no data), but I
> might choose a DAR primary cell, myself. You'll do fine with the UO, but
> I think you'd will like the DAR better over the long haul...
> http://www.oneilphoto.on.ca/oneilatm.htm

I agree with Jan all the way. The DAR cells are excellent, and are custom
sized for the I.D. of your tube. As for the secondary size, I'm using a
1.52" in my 8" f/6, and I believe the 100% illuminated field on mine is
about 0.40". That's plenty. Your system at f/6.8 is even longer, and the
longer the f/l of the primary, the smaller the secondary you need for the
same size 100% illuminated field. If you design your system such that your
focal plane is set 1/2" above the focuser's minimum height, you'll do fine
with 1.52", even on deep sky, and have a 19% obstruction. Good luck with it.

Howard Lester