NGC 7814 narrow field image

[H44]

I have been absent from the forums for a bit trying to get my new system going like I want.  First I want to say I am really impressed as usual with all the fine images everyone has posted.  It is such a delight to have such folk present on our forums!

I have managed to get my scope to track unguided for 10 minute spans with a very slight drift evident.  Just got this fine tuned this past Friday night.  Since I am mainly interested in tracking asteroids, neo's, pha's, etc. for astrometry, this is plenty good as most my exposures for that are only 60 seconds at most to get down to 19+ mag, and single frames are good for astrometry.

I decided to play a bit Friday night with some small galaxies.  

Here is an image I took of NGC 7814.  Not a widefield shot at all.  My camera/scope combo only allows me about a 9' x 6' frame so my tracking has to be spot on in order to not have elongated stars.  This was a total of two 10 minute exposures and seven 2 minute exposures with no guiding efforts other than PE correction.  This is a small galaxy at only 5' by 3' of arc.  My difficulty was the core burning in.  I'd like to hear from some of you how I can keep this from happening in the future.  I figure it would be a case to take some short exposures for the core and then long ones for the rest and merge them?



For details, see:
http://www.arksky.org/ngc7814_cascade.htm

Thanks,
Brian

[Jake]

Brian -

Glad to see it is all finally coming together nicely.  That is excellent performance for 10min unguided shots - I bet it took awhile to perfect the drift.

I would think that combining different exposure lengths would help you to overcome burning out the core.  I used that technique last spring on M42 to avoid burning the core, and it does work well - but requires a bit of finesse to get it to blend.  I am sure Rick and Steve can be more helpful than me, here.

It must be nice to be actually up and running after all the wait - I look forward to your upcoming images.

-Jake

[sc02492]

Brian, I am very impressed with this.  Your mount must be wonderful for you to produce such an image unguided!  As for core burn out, you will need to take shorter exposures and use masking techniques in Photoshop (or equivalent) to combine them with the longer exposure image.  Check out Jerry Lodriguss' site for more details:

http://www.astropix.com/HTML/J_DIGIT/COMP2.HTM

Steve

[ricksastro]

Looks like you have your rig humming!  10 minute unguided exposures at that extreme sampling is excellent!

Did your unstretched images have the core burnt out?  Or was it the stretching to bring out the darker stuff that caused the saturation.  If it was the later, then doing non-linear stretches (not stretching the whote side as much as the black) helps.    If the unstretched images were burnt out, then shortening the exposures is in order.  As long as you're over a minute or 2, there shouldn't be much if any penalty to taking more, shorter exposures.

I use masking as a last resort if everything else doesn't work...

Rick

[H44]

Thanks very much for the comments and suggestions guys.  I really enjoyed doing this the other night, and there are a lot more small galaxies out there I'd like to capture.  

Rick; all the singles had the core burned in too, even the two minute singles.  I also tried turning off the stretching in AstroArt, and various other things, but it did not help.

BTW, I did not use any dark frames, only a master flat.  Terry told me that this camera hardly needs one (a dark) unless I go quite a long time on a single.  There is quite a bit of readout noise unless I go longer than a minute.  Two minutes seems like the sweet spot to overcome that.

I'll try the masking technique next time.

I'd really like to try a digital Rebel on this scope...

Thanks!
Brian