From: Milton Aupperle <milton@outcastsoft.com>

Date: October 29, 2007 8:40:29 PM MDT

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] Re: Newbie question about real time viewing

Hi telescopaholic;

On 29-Oct-07, at 7:05 PM, telescopaholic wrote:

-----------SNIP---------

Additional details.

It's fairly easy to demonstrate solar systems objects at a public viewing.  What I want to do

is show deep sky objects from light polluted locales.  While a big Dob with filters works for

solo viewing, they're lousy for star parties.  So I've thought of two possible video

solutions:

A) B/W Firewire digital camera whose images could be processed on the fly to give near

real time display (as I outlined in my previous question above)

You can reach 30 times deeper with say 1 second exposures than you can with 1/30th of a second exposures. For you viewers, 1 second interval exposures aren't bad at all.

B) Supercircuits PC164C-EX (.0003 B/W Lux 600 line Sony Ex-Had)

I have owned two Supercircuits cameras attached to scopes that I used with a DFG/1394-1 Converter to display the video on the Mac, and the issues I had were :

1) The Auto gain is always on so I had no gain control unless you mod the camera. This tends to give you really horrific gain noise for faint objects. Also if you have dark and bright objects together, then you wind up the bright object being properly exposed.

2) The NTSC Frames are interlaced (odd even fields taken at 1/60th of a second intervals) and Interlaced video absolutely sucks when your tying to align images for image processing.

3) Maximum exposure time of 1/60th of a second.

You might be better off with something like StellaCam3 camera which was reviewed in Sky & Telescope September 2007 issue. The article shows what you get for different exposures with it, but it's also pretty pricey.

Either camera could be placed at primary focus.  Large Dob Mirrors are expensive because

they need to have short focal length to keep the eyepiece at a reasonable height.  However

if a camera is substituted for an eyepiece, a secondary is not even necessary and the

camera could be mounted on a spider at primary focus.  Yes the poles will be long, but

who cares if you don't have to climb a ladder.  As a matter of fact, now that the ladder and

focus board are eliminated, a cheaper light weight long focal length mirror could be used

and the upper assembly made much lighter, substituting tension wires for truss poles.

As someone else pointed out, the main problem will be achieving focus with anything like that.

So before I build such a monstrosity, do you think it will work satisfactorily?

One issue you haven't really addressed is that you will need to guide the scope if your going to try and do stacking. So a Big Dob is big light bucket, but without guiding it won't work really well at all.

Hope that helps...

Milton Aupperle