M35 / NGC 2168 w/NGC 2158

[rjbokleman]

I thought I might be having some issues with the AT130EDT as far as star shapes / reflections and wanted to see for sure. With only one night of good weather forecasted for a week or more, I went back to M35 which I'd shot a year ago with the SW100EDPro/Canon T5i for comparison.

The goal was to capture 80 frames each of RGB and 240 of L. I got a late start and while I got the 240 RGB frames, I only got 140 of the planned 240 L frames.

Using the PI Subframe Selector script, I only used 55 of each of the RGB and 117 of the 140 L for this image. In addition, I didn't make a single focus change between filters or for the duration of the capture session for that matter. Temps dropped 5-6 degrees over that period. Seeing varied a good deal over that same period as well. I just rotated through each filter event one at a time...which ate a bit of imaging time between filter changes / dithering every 6 frames, etc.

To try and boost the L channel a bit, I extracted the L from the combined RGB image using the CIE L* extraction, then used PixelMath to add the CIE L* frame to my combined 117 CLS/L frames before doing the LRGBCombine. Seems to have made up a bit for the lack of L, but not sure this is a good approach or not.

I was trying for a more natural sky/star result this time as the last attempt was a bit overdone with bloated stars and bit too high on saturation. Oddly, as things worked out, I ended up with nearly the same amount of data @ 2.0 hours....I guess Murphy is still around.

Anyway...I don't think there are any issues here with the scope. Only my processing skills.

Processing

Stack Bias frames to produce a MasterBias. No SuperBias!
Stack Dark frames to produced a MasterDark. No calibration w/MasterBias!!
Calibrate Flats w/MasterBias ONLY.
Integrate Flats into individual MasterFlats by filter.
Calibrate Lights w/MasterDark and MasterFlat by filter color. No MasterBias calibration!!
Cosmetically Correct Calibrated Lights
Subframe Selection of CC Lights
Star Alignment / Registration by filter
ImageIntegration w/Drizzle Data by filter
DrizzleIntegration by filter for final linear results.

Star Alignment / Registration of the LRGB Drizzle Lights
DynamicCrop by filter, but using the exact same DynamicCrop settings from a Process Icon.
DynamicBackground Extraction
LinearFit of RGB to L
RGB combination w/ChannelCombination tool.
BackgroundNeutralization
ColorCalibration

RGB
MaskedStretch of RGB
Extracted CIE L*

L
PixelMath of CIE L* + L
MaskedStretch - Tuned w/Curves

LRGBCombination
StarMask
MultiscaleLinearTransform
Invert StarMask
ColorSaturation boost, just on the stars a tiny bit.
Invert StarMask again
SCNR to remove a bit of red (0.50)
Final Curves

[rjbokleman]

One of the cool things about M35 is the double star ΟΣ 134 / HD41966 / SAO 78038 / TYC 1881-1595-1. The Golden/Yellow (Color Index B-V 1.4) (Mag 7.4) primary separated by 31.0" from its bluish (Color Index -0.03) (Mag 9.10) companion. It should be easy to spot in the image.

If you cannot find it, continue to the next post to help you out.

[rjbokleman]

STT 134 Diagram

[Chuck]

Another great shot and comparison to last years image with the DSLR. Looking back at last years image, I have to admit I like both about equally. I'd like to try imaging that region with my setup sometime. If I could get a fraction of your quality I'd be happy. --- Chuck

[Apollo XX]

Cool, Ron. A couple of beautiful clusters you've captured there!

[rjbokleman]

From a purely imaging point of view there's some other details here. The ASI1600MM-C is a 12bit ADC, the Canon T5i is a 14bit ADC.

What that means is that with the same data capture period the ASI captured photons with less precision than the Canon and yet did pretty well representing the photons captured as far as true color/dynamic range is concerned. Hence my post about the star colors here.

This is a big difference between CCD cameras as far as cost is concerned as they are true 16bit chips with greater precision.

This affects everything from Dynamic Range to noise. In the case of the ASI, being 12bit, you have to stack more frames to get an equivalent quality image that would compare to a smaller stack with a DSLR or CCD due to bit depth.

This is rather a fascinating topic in its own right.