M13 but lacking colour - possible problem with Nebulosity settings

[David_Pickles]

Sometimes things don't quite work out as expected. My latest image - M13 The Great Cluster in the constellation Hercules - is the first DSO I have imaged for quite a few weeks and the first I have taken using an Off Axis Guider instead of a guide scope. This should have been enough to warn against making too many other changes, but I also decided to try out the latest version of Nebulosity 3. I used to use Nebulosity 3 as my camera control software with my Canon EOS, but when I upgraded to the QHY8L CCD it wasn't compatible so I started using EZCap - the software that comes bundled with QHY CCD cameras. However, I recently found out that Nebulosity 3 now supports the QHY8L so I thought I'd give it a go and I actually got on really well with it - until it came to processing. I'm not really sure what went wrong, but my image seems to lack colour. There is a hint of it in there, but not much.

The image was captured using my QHY8L camera attached to a Sky-Watcher Explorer 190MN Pro with a Tele Vue 2x 2" Powermate, guided using an Off Axis Guider and Starlight Xpress Lodestar guide camera. It is the result of 10 x 180s images, captured and stacked in Nebulosity 3 and processed in Photoshop CS6. I believe that Nebulosity may have automatically debayered the image prior to saving it to disk - obviously the settings must have been wrong. Whilst I think it is a lovely image, showing lots of detail in the cluster, I am a little disappointed that it does not show the beautiful star colours. Next time I will do a sample run with Nebulosity first to see if I can get it working, otherwise I will have to revert to EZCap.

[David_Pickles]

Finally managed to work out what went wrong with this. Firstly, I had it setup to save compressed images rather than raw data, but secondly, I needed to adjust the gain and offset in Nebulosity as I think my earlier settings may have been too high - I'm now using gain setting 3 (4%) and offset of 113.

M13 - The Great Cluster by -Judge.pickles123-

[PhotoGav]

Well done, that looks so much better now! Worth persevering with the head scratching and enjoying the moment of success when you get the result!

Lovely image of a great target.

[cosmicdonkey]

Cracking image

[David_Pickles]

Thanks for your kind feedback. Hopefully (if the weather holds out) I may be able to give this one another go with the 2 x Powermate again this evening.

[jezhughes]

Hey David

Was that with the qhy8L?  Each has its own slight variant gain/offset setting. You can work it out with a guide - http://qhyccd.com/en/top/manual/qhy8l-1/qhy8l-chapter3/

You might have the slightly wrong settings, i guess? You've sorted the RAW issue (I made the same error with mine at first), but getting the right gain/offset might get the most out of the camera

[David_Pickles]

Thanks Jez - you are right, the gain/offset was a little too high in Nebulosity. I had set the QHY8L up as per the instructions above when I first got it using EZCAP, but assumed the settings would be the same in Nebulosity. I went through the process again last week and came up with gain setting 3 (4%) and offset of 113.

[julianr]

My qhy10 settled down after a few months and I had to use less gain couldn't find out if this was common or not. Anyway all worked fine after I changed it

Sent from my GT-I9300 using Xparent Skyblue Tapatalk 2

[David_Pickles]

Interesting point Julian - I had not considered that the settings may change over time.

[David_Pickles]

My latest attempt on this target. I think I can safely say the the colour issues I had on my first attempt have been resolved and the Powermate is doing a good job at increasing magnification and detail. I'm quite pleased with how this one has turned out

[Steve 1962]

Well done David - they're lovely images - very natural looking

Steve

[julianr]

Yup come out well. I never did find out why my gain needed changing but the new settings worked from then onwards

Sent from my GT-I9300 using Xparent Skyblue Tapatalk 2

[David_Pickles]

Thanks Steve - I like to keep the image processing fairly minimal if I can.

[David_Pickles]

Thanks Julian!