Re: 20" RC on AP1200

Jul 21, 2006



#15521 Jul 21, 2006

--- In, "ocular21" rbissinger@...> wrote: >

> Reviewing some previous threads on this list as well as on other

lists > still leaves me wondering if a 20" truss RC could be managed by an

> AP1200GTO. Would appreciate hearing from anyone with direct

experience > with such a setup, thanks.

I'm using a home made 18" f/12.6 (F=5700mm) truss tube classical

cassegrain on my older AP1200GTO and am getting fine results so long

as the wind is light (~5mph) or non-existent. The telescope weighs

about 120# with full instrument load on it, possibly a tad less.

I believe that a 20" Truss tube RC such as the RCOS one would work

about as well on the mount, but both are basically approaching the


here's a recent shot from my 18"/ap1200gto:


I am getting stars in the low 2s this week with the good seeing I've

been experiencing and that is for 30 minute subexposures and guiding

is conventional (ie non-AO7) guiding.

One person mentioned to me that my star diameters were smaller and my

nebula better resolved than images of the same object taken with a

20" RCOS in Mayhill, NM and a 16" RCOS at Kitt Peak. It is too bad

those images were shot in RGB or LRGB because it make them a bit

harder to compare since narrowband filters greatly attenuate star

intensity so they have stars in their images that do not appear in

mine. Still FWHMs of stars and nebular resolution can still be

compared though.

Obviously seeing usually is the deciding factor and I'd like to see

the performance of the respective systems in side by side test at the

same time in the same location. But with the limited data I have so

far I think I am 'in the hunt' so to speak.

By the way my mirror has a chip out of it about 4" square due to an

unfortunate accident a year and a half ago, but it seems to be

working well nonetheless.

I am happy with the AP1200s ability to handle my load though.


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