How far can I reasonably push this set-up?

[Joel Shepherd]

I realize the set-up I'm going to describe is not the best for AP. I'm okay with that because I'm still learning the ropes and my own preferences.

I have a Celestron Omni XLT 150 -- 6" Newtonian reflector -- on a CG-4 GEM mount. A completely unmotorized equatorial mount. I recently acquired a monochrome Orion G3 Starshoot CCD camera. My first night out with the camera was okay: typical Orion nebula with blown-out center and soft stars (11 decent 1.5 second shots stacked and stretched).

Given the inherent limitations of this setup -- especially the lack of any guide motor whatsoever -- are there any tips/tricks for getting the best possible images from it?

A few things that I'm going to do differently next time are:

  * Gain adjusted slightly downward to avoid fully-saturated pixels.

  * Better focus, better focus, better focus.

  * Anti-vibration pads (we're on a pretty well-traffiicked road).

  * If possible, 1x1 binning.

I'm wondering, in terms of exposure time, how long I can go with a completely unmotorized mount; whether any sort of focal reducer is feasible (without replacing the focuser itself), and if there is anything else I can do to get the best possible images from this setup. (For reference, I'm primarily interested in fairly bright DSOs: bright nebula, Andromeda, star clusters, etc.).

Looking forward to any thoughts or shared experience -- Joel.

[hjw]

There is a kind of rule of thumb: 600 divided by the focal length in mm equals max exposure time in seconds. So with 1.5 seconds you are at if not beyond the limit. Sorry!

[ronin]

Little obvious but why consider buying a focal reducer but not a set of motors?

Thoughts being spend the money on the bits you need and not the bits to make little if any improvements.

A focal reducer will make smaller (possibly) stars and may add half a second to the exposure length, motors will not make any difference to the star size but will enable 30-60 second exposures, if the polar alignment is good.

[Joel Shepherd]

Thanks for confirming my suspicions about the limits on exposure times: I still need to wrap my head around the math but suspected that without any form of guiding they'd be very small.

My hope was that a reducer, besides giving a wider field of view, would enable slightly longer exposures by reducing the star trail effect (wider field on single pixel: more time before a point of light drifts to the next pixel).

When you say "set of motors": do you have something specific in mind? I know Celestron sells basic motors for the mount (which now that I'm looking seem to get better reviews than I'd remembered). Are there other options to consider?

Thanks again for the feedback! -- Joel.

[glowingturnip]

I've got an Omni XLT150 reflector and a CG-4 with an after-market Synscan kit on it, and it does the job very nicely - a kit something like this...   http://www.teleskop-express.de/shop/product_info.php/language/en/info/p3235_Synscan-GoTo-upgrade-kit-for-EQ-3-and-CG-4-mounts.html though I'm sure it didn't cost anywhere near that much...

Once I'd coupled that with a guidecam and scope, I can get about 5 min exposures from it without throwing away too many eggy ones.  Some of my pics on my flickr link.

Mind you, I am starting on the long process of convincing the other half that an HEQ5 pro or an EQ6 would make a good investment...

[Joel Shepherd]

Hoowha. Yes, for that price I could/should just buy a whole new tripod and mount. :-)

Your pictures are inspiring, though, which makes me think that with some modest expenditures and a lot of practice I might be able to get some decent images from the rig I have.

Thanks, folks, for helping me prioritize my next steps.  :-)

-- Joel.