Re: Pelican Nebula and M33

Robert Chozick <rchozick@...>

Thanks Stuart.  I think we have had this discussion before.  I do use Photometric Color Calibration in PI.  I pre process in Nebulosity (I am a Mac user) then I go to PI and use SCNR to remove green, Photometric Color Calibration and DBE.  Then I go back to Nebulosity to use its Digital Development for its final stretch to a 16 bit Tiff for Photoshop.  Then I finish the rest of the way in Photoshop.  I have attached what M33 looked like when it went to Photoshop:

I did a quick processing in Photoshop without the galaxy color change described below.  I just took a bit of green out.

When I do galaxies I use Curves in Photoshop to bring up the red in the core and blue in the arms.  These are slight adjustments at specific points with the opposite color being reduced where the other is increased.  I manually play to create which part of the galaxy becomes core and which part starts the arms.  I know this is not kosher to many but I am not trying for exact reproduction.  I think of it as art more than science.  In the end I am not trying to get the exact colors just what looks nice to me.  I do think I overdid it the effect on this one.

Again the version I posted tonight

I did M33 a while ago without doing the color correction.  This one was LRGB plus a good amount of Ha.

I intend to get a lot more subs of M33 and also adding Ha.  The one I posted tonight was really only meant to be a test of the new camera.


On Aug 1, 2020, at 8:09 PM, Stuart <stuart.j.heggie@...> wrote:

Robert, both of these shots are really nice! I have been going back and forth on them and wonder about the constraints that OSC cameras put on you for colour. How do you calibrate them for colour? I shoot monochrome with filters and use PixInsight's PhotometricColorCalibration tool which is simply amazing. 

I mention this because the M33 shot seems like it could stand a tweak on colour but not an arbitrary one to "make it look like everyone else's". You mention that you use PixInsight. Have you tried that calibration tool?

On Sat, 1 Aug 2020 at 16:48, Robert Chozick via <> wrote:
I got a few more images from my test trip for my new ASI2600 CMOS color camera. 

Pelican Nebula

The bright stars in the Pelican got blown out and really unfixable with the shorter exposure subs so I learned that 5 min at f5 is too much with this camera when bright stars are present.  There was also a reflection in the right upper corner that I think I can fix by bringing the UV-IR filter closer to the sensor.  On the FSQ the CA-35 camera adapter allows a 2 inch filter to be screwed in but it is 30-40mm away from the sensor.  I am getting a ZWO filter drawer to bring it closer.  Hopefully that will fix it. 


I needed more data on M33 and some Ha but I was surprised at the quality of the data for only 2.5 hours.

I need to try to always get more data on images.  In the past I have wanted to get a lot of images on every trip since it is so rare I go but I am going to try to get at least 5-6 hours of data at f5 and 8-12 hours at f8 from now on.

Robert Chozick



Robert Chozick

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