Full Moon and Training for Imaging

[lazjen (Chris)]

For the first time in about a month, the sky is clear, I'm home and I've got my gear ready to assemble/test/etc.

But, of course, it's a full moon. And while it's quite interesting itself, it does tend to light up everything...

Given my setup (see sig), what types of training activities can I do at these times to improve my imaging attempts when the conditions are more ideal?

Doing polar alignment practice is a given. Now that I've marked out my spot in the backyard using 3 round cement pavers, I'm finding that getting a reasonable polar alignment after setup is getting quicker as I have less variables to modify (level was spot on again, for example).

I tried to do some guiding, but I struggled to get decent signal for PHD to work with. I am assuming this is because of the moonlight washing out the whole sky, but I'm not 100% confident in my guide camera setup yet - I've only just put the bits together recently and while I think I've cracked the focusing distance required, I haven't had a chance until now to really check.

I noticed while doing my star focusing that they were twinkling and dancing around a lot - so I assume the upper atmosphere was turbulent? Are there any websites around with timely wind data that I could use to cross-check the assumption - or other ways I can tell for sure? It would be useful to know to eliminate it as a variable, or to know just how limited I'm going to be in a session.

Thanks for any help.

[ZeroID (Brent)]

Hi Chris, lucky you, clear skies at least. Cloud and rain here.

How about globs ? With a LP filter to kill some of the skyglow you should be able to pull some short exposures and get some pix. Also guiding is not so critical or even required if your alignment is good for short exposures.

[lazjen (Chris)]

Ha, indeed, it's been mostly cloudy, some rain. Lots of days where I was teased with near clear skies only to have it come over cloudy towards the evening.

I'll have to look into a LP filter, I guess. What sort of exposure time/ISO are we looking at here for globs?

[ZeroID (Brent)]

Globs at 800 ISO can be as short as 5-10 seconds and you can bump the ISO as the noise factor is minimal for the exposure time. I normally take about 20-30 and stack them as per usual. More is better, discard the duds.
If you can get alignment good 10-20 secs will do better on the fainter globs and stars in them.
Don't worry aout the LP filter for now, you can process that out with noiseware and some curves. Start shooting.
Experiment and see ... a bit of judicious procesing can pull a lot out of minimal frames.

[lazjen (Chris)]

No worries, I can do that. Clouds seem to be coming back, so I'm probably doomed again for a few days.

In my OP I mention trouble with getting good signal for guiding. I put this down to the light levels with the full moon. I'm still wondering if this assumption was correct. Can anyone confirm this?

[naskies (Dave)]

Originally Posted by lazjen

In my OP I mention trouble with getting good signal for guiding. I put this down to the light levels with the full moon. I'm still wondering if this assumption was correct. Can anyone confirm this?

I have a smaller scope than you (RC8) and have no problems with guiding under a full moon (with Lodestar or ST-i guide cameras).

What do you mean by "getting good signal"? Are you using a reducer at all? At native focal length, your ST-i has a field of view of 8.24' x 6.16'... so it's quite possible that you just didn't have a bright star in your field of view Have you tried rotating your image train to look for a brighter guide star, and/or nudging the telescope around?

[lazjen (Chris)]

Ok, I've just recently got my setup assembled with the DSLR and OAG in place. Previously to that I had the ST-i using the main scope for guiding and the DSLR piggybacked on top. I was able to get PHD working in that combo once I got the ST-i reasonably focused and was careful with stray light (a problem in my backyard). I have noticed that the ST-i is quite sensitive and PHD would get "upset" if the captured image was made excessively noisy - whether by bad focus or the extra light. So while I was getting some stars appearing in the image through the OAG the other night, the images were quite noisy and therefore PHD complained a lot.

With your statement though about guiding under a full moon, I now know that I have not sorted out my focus distance correctly for the ST-i and that the poor signal for PHD was probably bad focus images. More work required here then.

At this point, I'm not using a reducer, just a field flattener.