First NB/HST attempt - NGC 2237 Rosette Nebula
Posted 02 February 2013 - 03:11 PM
A buddy was gracious enough to let me borrow his modded XSi and some Astronomik clip in filters (Thanks Austin!), so I decided to try my hand at a HST image. This was also the first time I attempted to do 10 minute subs, and I have to say the mount handled it pretty well. I have to say, it may be hard going back to my plain ol T1 after this, lol.
Any recommendations on NB processing, color balancing etc would be greatly appreciated.
Posted 02 February 2013 - 11:16 PM
You did a great job with your first narrowband image. You captured some excellent details in this image as well as nice outer faint regions. Your mount definitely handled the 10 minute subs without a problem, as I don't see any evidence of trailing. Take a big bow for your first NB!
As far as color and processing - I'm not speaking from any experience, as I've only done a very limited amount of single band (Ha) narrowband imaging. But, I think many of the ways we process RGB is quite applicable to false color narrowband images. Namely, I think most NB images look best when the background is fairly neutral, the contrast and brightness are reasonably high, etc. As far as what colors to use - well, its false color. So, anything that looks good to you is probably a good color balance.
With that in mind, I can see that with this image your color channels are rather misaligned. If you look at your histogram, the blue channel black point and peak are well to the left of the red and green channels, and your green channel is a bit lower than your red channel as well. This manifests itself as an overall yellowish background and yellowish tinge to the image.
For my taste, I like my images to be more neutral. I hope you don't mind, but I took the liberty of doing some adjustments to your version which made it more pleasing to me (recognizing that false color images are truly a matter of personal taste). My adjusted version is at http://tinyurl.com/bfgkswh.
In general, I aligned the RGB channels (the red channel with shifted a pixel or so to the upper left and the blue channel was shifted about 1/2 pixel to the lower right), I neutralized the colors, used Gradient Xterminator to minimize the gradient, ran HLVG to remove some of the residual green cast, did a few curves to brighten and increase the contrast, a little selective color adjustment, and some final levels. If you're curious to see my actual layers, you can download my Photoshop .psd from http://tinyurl.com/b6he69c (5.7 MB).
Its quite likely that you may prefer an entirely different color balance, but this might give you an idea about alternatives.
Again, excellent first dive into narrowband imaging - it looks like you had a lot of fun with it!
Posted 03 February 2013 - 12:06 AM
Yeah as far as the color balance went,I wasn't sure how the rules applied as far as colir balance so I didn't even look at the histogram. Lesson learned! Your version looks really good. I will try your suggestions when I get home.
Posted 03 February 2013 - 05:59 PM
Posted 03 February 2013 - 11:18 PM
Posted 03 February 2013 - 11:50 PM
I like this image a lot!
This is the 1st image I remember seeing with SII taken using DSLR. I think it came out pretty well, comparable to CCD images of the same object.
Did you get a lot of SII signal? Would you mind to share data for separate channels? What kind of modification your camera has - clear glass or other?
Posted 04 February 2013 - 12:15 AM
Posted 04 February 2013 - 01:12 AM
Terry, I agree that CCDs are better for NB but right now my budget won't allow it, and I'm not sure the extra resolution is worth the cost on top of learning an entirely new workflow.
Alex, the camera is a clear glass mod. I was shooting at f/2 with Hyperstar so that helped pull in a lot of light. I'm going to attempt it on the 6.3 reducer and see what kind of results I can get. My SII data is below.
Thanks again Scott!
Posted 04 February 2013 - 06:08 AM
Alex, the camera is a clear glass mod.
Just wanted to chime in and say its actually a full spectrum mod with the entire filter assembly removed. Nothing in front of the sensor.