Re: [APML] need advice on camera mount

[Jerry Lodriguss <lists3@astropix.com>]

Hi Wei-Hao,

Personally, I believe in over-mounting everything.  It's hard to tell about 
the Takahashi Guiding Mount TGM-2 because I can't get a sense of scale from 
the picture.

I use a lot of Gitzo stuff, and I think it's great, but I wouldn't ask it 
to do what you want to do... just my 2 cents.

If you do end up going down this road, make sure you mount the 
camera/rings/plate to whatever you put it on, with more than one screw, 
because it will pivot with just one, probably during an exposure.

Also, one screw at the bottom of the mount, whichever you choose, is likely 
to pivot also.

If you were going to shoot with a digital camera, and limit your exposures 
to 3 to 5 minutes, you might get away with this kind of rig. If you're 
going to shoot film and expose for 30 to 60 minutes, I would doubt it will 
be consistently successful. You may get away with it in certain 
orientations, but not in others.

I don't have any personal experience with the Arca-Swiss monoball head, but 
it's rated capacity is a lot more than the weight of what you want to put 
on it, so that would be in its favor. The problem is that these things are 
generally used in a studio and not for 30 to 60 minute exposures on a scope 
tracking the stars. Even if the monoball head was rock solid, if you 
conventionally mount it with just one screw on the bottom and one on the 
top, I would be very afraid of something pivoting and moving during the 
exposure.

When I shoot with a 300/2.8 and 400/2.8 on top of my 130EDT f/8 refractor, 
I have them mounted on a 3/8 inch thick aluminum plate that has one hole at 
the back end, and a slot on the sky end. This gives me a couple of degrees 
of aiming flexibility in declination and I can lock it down rock solid, but 
no where near the 15 degrees you seek.

Jerry


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