M51 with 127 MAK and QHY5LII-M

[turfpit]

Captured 9th April 2019 around 22:00. Thin high cloud and intermittent lower cloud.

__M51-78x30s-g6-o10.png (205.67 KiB) Viewed 2739 times

Equipment: Celestron AVX mount, Skywatcher 127 MAK, QHY5LII-M, TS 0.5x reducer.
Frames: 100 lights, 50 darks, 50 bias, 50 flats.
Software for capture: SharpCap 3.2, FITS Liberator (to establish offset value and check light frame before imaging run).
Capture settings: Expsoure 30s, gain 5, offset 10.
Software for processing: SiriL 0.9.10 to calibrate, register, stack, crop, apply background extraction and histogram transformation. Final processing in GIMP 2.10 > Curves, Levels, Contrast, Noise Reduction.

Due to the passing cloud, 13 of the 100 frames failed to register. The best 90% were stacked - hence the 78 lights actually used.

Histogram of final image in GIMP:

_histogram.JPG (18.83 KiB) Viewed 2739 times

Capture in progress. 1280x960, FITS, MONO16, exp=30s, gain=6, offset=10, display histogram stretch applied.

ready-to-capture.JPG (57.62 KiB) Viewed 2739 times

I think I will revisit this with an IR Cut Filter and slighty up the exposure as the capture histogram is weak.

Not too bad with modest equipment and less than ideal conditions. A bit of progress since November 2016

M51-processed.png (66.87 KiB) Viewed 2737 times

Dave

[QHY5LII-M]
Output Format=FITS files (*.fits)
Binning=1x1
Capture Area=1280x960
Colour Space=MONO16
Pan=0
Tilt=0
Force Still Mode=Off
Enable Live Broadcast=Off
USB Traffic=0
Speed=1
Offset=10
Amp Noise Reduction=On
Frame Rate Limit=Maximum
Gain=5
Exposure=30000
Timestamp Frames=Off
Contrast=0
Brightness=0
Gamma=1
Banding Threshold=35
Banding Suppression=0
Apply Flat=None
Subtract Dark=None
#Black Point
Display Black Point=0
#MidTone Point
Display MidTone Point=0.5
#White Point
Display White Point=1
TimeStamp=2019-04-09T20:45:49.3977050Z
SharpCapVersion=3.2.5926.0

[turfpit]

Here are some screenshots of the preparation for capture & subsequent processing.

Focusing with Bahtinov Mask, Zoom 200% and use display histogram stretch:

M51-focus.JPG (55.07 KiB) Viewed 2737 times

Establish offset via test bias frame with centralised histogram:

bias-frame.JPG (117.13 KiB) Viewed 2737 times

Flat frame capture, used home made flat panel generator, histogram set to 40% - 50%:

flat-frame-capture.JPG (48.62 KiB) Viewed 2737 times

Why flat frames are needed:

why-flat-frames-are needed.JPG (72.84 KiB) Viewed 2737 times

Master dark frame:

master-dark-frame.JPG (72.1 KiB) Viewed 2737 times

Master bias frame:

master-bias-frame.JPG (62.78 KiB) Viewed 2737 times

Background extraction:

background-extraction.JPG (91.66 KiB) Viewed 2737 times

After background extraction (no signal from object):

after-background-extraction.JPG (37.25 KiB) Viewed 2737 times

After being calibrated, registered, stacked. Note the stacking artefacts due to tracking being off, I really must get round to implementing PHD2:

calibrated-registered-stacked.JPG (56.68 KiB) Viewed 2737 times

Dave

[numchuck]

Thanks , Dave ,

for showing all of your work . Makes me realize how much more I have to learn . Can you talk more of your image that shows "why flat frames are needed"? I want to learn how to evaluate my own set up and how to improve things with flats . I can see easily what my dark frames are doing ; but that's all that I've learned to do , so far . Thanks , again .

Chuck

[turfpit]

Thanks Chuck.

If you look at the capture in progress image (which has a display histogram stretch) - the black dots are the dirt in the optical train. In the flat frame capture image the corresponding black dots can be seen. When the master flat is applied to the light frames, the imperfections in the optical train are removed. The stretch master flat image shows how bad things really are - there is dirt (the black dots), rings (dried dew) and very slight vignetting (centre brighter than outer edges). The vignetting would be more pronounced on a larger sensor camera (the QHY5LII-M is 1280x960). To stretch the master flat use whatever processing software you have or load into the SharpCap test camera and use 'display histogram stretch'. FITS Liberator would do this https://www.spacetelescope.org/projects ... load_v301/.

I hope the above answers your questions.

There are some important points in my post:

• The equipment is modest, a smaller budget scope and a guide cam. Ok, the image is no APOD.

• Intermittent cloud, the wind was also around 10mph.

• The mount tracked the object for 50 minutes unguided. Means my polar & mount align were decent.

• Reasonable focus was achieved using just a Bahtinov mask, best £20 I ever spent on this hobby.

• I have shown the steps that I go through to try to get the best from my captured data.

• The resultant image is a big improvement over my first M51. Not ashamed to show that as that is reality.

I think I can probably do better with the same equipment and better conditions (plus use of an IR Cut Filter).

My images, gathered with a variety of hardware and software are here https://www.astrobin.com/users/turfpit/.

It is my belief that by taking the time to understand the basics I will over time be able to substantially improve my images.

Dave

[numchuck]

Thank you very much , Dave , for your answers . It's amazing how addictive this hobby has become .