M33 - 25 min

[Emanuele]

Dear all,

I didn't want to process this 5, 5 minutes subs, for a total of 25 minutes, of M33 that I got the other night.
It was very low on the horizon.
Anyway, didn't have much to do yesterday night and couldn't sleep so I thought I would give it a go at processing, but the data is not enough at all!

5 x 5 minutes
Pentax 125 SDP
SXVF-M25C
Em200 guided with mini Borg 50

Bigger image (1500px)
http://www.backyardskies.com/BackyardSkies/M33_Information.html

Smaller preview:

[spearo]

Looks fine to me
obviously more subs will enhance the s/n and smooth out the galactic arms but looks great as is
cheers
frank

[Hagar]

Hi Emmanuele, Looks a pretty respectable image. Longer almost always give better results but time constraints always come into play. You can always add more data to the image at a later date.
Still a very nice image.

[gregbradley]

Very nice shot for little exposure time. Your Pentax 125 I believe is a fantastic scope and the MX25C is a proven performer.

A couple of tips.

One shot colour cameras generally have quite a bit lower QE (sensitivity) than mono. The mono version of your chip is probably around 60% QE (percentage of photons converted to electrons) whereas the colour chip is probably more like 26%.

What this means is that you will get a lot more noise in the dim areas of the image.

For example if you take one of your images taken so far and zoom right in on a dim area you will see lots of M and M type red green blue dots that are colour noise.

The way around this is:

1. Take the longest exposure time you can for your tracking before stars go eggy - like 15-25 minutes. This gives the signal a chance to build up slowly and get past the noise levels.

2. Keep in mind this factor of colour noise in the dim areas so if you are working out exposure time go as long as you can on dim objects and you can go shorter only on bright objects. So brighter objects will come out nicer than dim objects.

3. Always slam the camera down to the maximum cooling it will go to.
You can select adaptive darks when processing if you get an odd temp like -22C. Its better than getting them all at -15C and more noise. -35C is a good temp for CCD chips generally speaking. This will be hard to achieve in Florida so whatever you can get the lower the better. Perhaps consider water cooling assist to get that extra 10C cooling. It'd be worth it.
I had an STL11 one shot colour and at -35C it started to sing but it was a bit croaky at -15C so to speak.

This factor of colour noise in the dim areas is probably the main constraint with one shot colour cameras and that is the best solution - minimum 15 min subexposures and 20 - 30min if your tracking is up to it.

Its a matter of knowing the limitations of your gear and working around them to get the best results.

Greg.