Another M51

[numchuck]

I'm still learning but I did this last week with SharpCapPro and my ES127 and QHY183 . 20 dark frames with 8 second exposures totaling 156 minutes , dithered every 30 frames and processed with StarTools . The clouds ended my session early ; but I was happy with how the center of the galaxy revealed itself .

https://drive.google.com/file/d/1I59-i5 ... p=drivesdk

[turfpit]

Some great detail in your M51.

Dave

[numchuck]

Thank you , Dave . This is the first image , where my guiding has helped me , rather than , hurt me . I need to dither , to keep down the fixed pattern noise ; but otherwise , I would just let SharpCap run by itself

[oopfan]

Great work, Chuck!

Let me see if I understand:
Explore Scientific ES127: 127mm f/7.5. Focal Length: 952.5mm
QHY183: 2.4um pixel size. Is it Color or Mono?

According to the CCD Suitability Calculator https://astronomy.tools/calculators/ccd_suitability
With Exceptional Seeing you are slightly under-sampling.
With Good Seeing you are neither under-sampling nor over-sampling (this is a good place to be!)
With OK Seeing you are slightly over-sampling.
With Poor Seeing you are over-sampling.
With Very Poor Seeing you are greatly over-sampling.

Chuck, I don't know what your seeing conditions are like but mine are "Poor". With my scope and camera I am slightly under-sampling. If your seeing is anything like mine then you are over-sampling. Given a choice I would prefer to be over-sampling like you!

The ES127 is a fine APO and when you add in the over-sampling plus great guiding it is giving you excellent detail.

Clearly the quality of your scope is the greatest influence but what of the positive effect of over-sampling?
I would interested to know what you think. Have you tried other cameras with your scope?

Thanks,
Brian

[numchuck]

Thank you , Brian . I am , for sure , over-sampling , even when binning at 2x2 . Now , I don't know if this is relevant ; but in StarTools , I can bin , again , in processing , but in fractional increments , supposedly . These images have been processed that way , slightly , at what StarTools labels as 75% . I had tried 50% , which would have been closer to an additional 2x2 bin in software ; but that clearly removed detail from my images . I want to try again with no software binning ; but I am not certain of what I am doing when it comes to processing . I just need to experiment . Anyway , I haven't tried other cameras ; but I was thinking , some day , of a color version of the 183 . Would that camera , have less , wasted resolution , than my mono ?

[oopfan]

Actually I prefer mono cams over color. Much better image quality in my opinion but it comes at the cost of more effort to make a color image (i.e. LRGB). With mono cams, a common configuration is to use bin1 with the luminance filter and bin2 for RGB. bin2 greatly reduces exposure time but at the cost of lower resolution but that isn't a problem. On one of my websites I excerpted something that Trevor Jones said:

I think it was Trevor Jones at AstroBackyard who made the analogy of a child and his coloring book. The child provides the crayons and the publisher provides the detail in the form of the outline. If the child draws a little outside the outline the picture still looks good. If he gets sloppy it gets worse but is still acceptable especially if seen from a distance. This is the analogy that Trevor made with binning: bin2 is like the child drawing a little outside the outline, and bin3 is sloppy but acceptable. Remember that the outline is the job of the luminance filter running at bin1 and since the sensor sees three times more photons the exposure time is reasonably short.

I did a quick search for 'binning' with the QHY183 but came up empty. My opinion is, it's a mono camera, they got to support bin2, right?? Who knows, I'm not a big of CMOS anymore. I love the 16-bit A/D in my lowly $400 CCD camera.

The problem is that my pixel size is 4.65um which is too large for my scope's 418mm focal length. Like I said I am slightly under-sampling at bin1 but bin2 is terrible. In fact I've given poor Mabula Haverkamp at AstroPixelProcessor (APP) quite a workout trying to get my bin2 images to process. I wish I had your problem of over-sampling, my images would be much higher quality. I think that is one reason why your M51 came out so well, that plus your APO. There are only two negatives to over-sampling: (1) the image is less bright so your exposures need to be longer, (2) your images are more sensitive to guiding errors.

Regarding StarTools, I used it for a number of years until someone recommended APP. StarTools was/is quite the bargain. I think I paid $50 for lifetime access. I've used the Binning tool before but only to hide the noise in an image. I've never been a great fan of denoising software so a lot of times I just scale the image down. Lately I've been using GIMP for denoising. They have a filter called a "Selective Gaussian Blur".

Getting back to the mono vs color debate. Back a couple years ago when I had an ASI120MC I noticed that faint stars did not have good color reproduction but you might not have that problem since you are over-sampling.

One other thing to mention about binning... true hardware binning will reduce noise, not so with software binning. That's just something to look for when making a camera purchase.

Brian

[numchuck]

Brian , thanks very much for your answers . I really like the color book analogy . I hope to one day , try my hand at LRGB imaging ; but right now , I'm super happy just to finally "see" detail in the galaxies that I've stared at , all my life , through an eyepiece . I never imagined that I could have such a "view" with my own equipment . This one photo is , by far , the best image I've ever managed ; but now I'm looking forward to getting more .

[nexusjeep]

Nice shot of M51 I tend to dither a little more often now perhaps every 3 - 4 frames since Robin made the alteration to SharpCap to reduce the exposure time by doing this you lose hardly any imaging time, the only thing I do set is to reject on brightness in the live stack and set the threshold at 50% as sometimes I have had it add the 1s dither frame to the stack which messes with the histogram somewhat. Your scope has slightly more focal length than my refractor so you get a slightly larger view of M51 over me it is a very interesting galaxy to image.

I have a mono ASI1600 that I have used a fair bit in narrowband but recently have purchased a ASI2600MC Pro as in the UK the weather can sometimes be a challenge and kept leaving me with unfinished images hence the colour camera. Like Brian has said the mono is more sensitive / sharper but it depends how large you are blowing things up. Also I must say I actually enjoy the simplicity of processing the colour images lately.

The fun part of this hobby is the continuous journey of learning / trying new things as well as the other members of this forum posting images and information as it can only be good for the community and hobby and we are never too old to learn /try new things. Also in the current lockdown it is one of the things allowing me to maintain my sanity although I am in the fortunate position to be able to work from home.

Keep the images coming.

Cheers
Nick

[numchuck]

Thanks Nick . You are right . I should dither more often , as well . My background would have looked improved . But I was anxious to get as much exposure as I could get , before the clouds rolled in . There are so many settings combinations to try . I just don't fully understand what I am doing yet .

[oopfan]

I know I keep harping on it but you can improve your background without dithering by increasing exposure. Remember that the sky is a part of your image every bit as much as the faint nebulosity. In order to clearly separate faint nebulosity from the sky your sky needs a high enough SNR. If you choose short exposures then your sky drops to the bias level which puts you at risk of raining noise. You don't need to dither to get great astrophotos. I've proven it over and over again.

Brian