Please critique my image (M45)

[CaptainShiznit]

Hey, so I'm aware my final image is terrible which is why I'm asking for help. I was hoping someone could point out mistakes that I've made either post or pre processing. I've included my stacked image as well as my processing attempt in case anyone wants to have a go themselves. I'll also include a link to download my raw data in case anyone wants to stack it themselves:

https://drive.google.com/open?id=1LuN_kNZYl4QpNeTvxiYHfQzhkthJf4bg

I used Photoshop for processing and it's still very new to me. All I've done is levels and curves, GradientXterminator and various action sets.

Capture details:

SW 130PDS / HEQ5 Pro (Belt modded) / Canon 600D (unmodded) / IDAS D2 LPS filter / Baader MKIII MPCC / 180s subs (unguided)

Captured in APT.

Just looking to learn and improve. Cheers.

m45.TIF

[carastro]

The image is not too bad, but there are some big gradients in there.  I did an iteration of gradient exterminator which improved most of it but left a wide gradient all along the bottom.  In order to do any more processing I just had to crop that off otherwise any further stretching just made that worse and it spread up the image. 

This is how it came out.  I think the only capture fault was the subs need to be longer 300 secs. 

Carole 

[tooth_dr]

I had a quick play with your TIFF file:

There is some nebulosity coming through on Merope, good job.  I would maybe say that yours is too dark, the focus or collimation is slightly off, and there is some drift.

[alacant]

Hi

Excellent shot.

I agree with @tooth_dr that it's a bit dark. Here it is within a mm of its life. The nebula is showing a bit. Add more frames and you're onto a winner.

Cheers

[Aramcheck]

I had a play with the dataset, but couldn't achieve anything decent. To me it looks like you had stray light getting into the OTA & unfortunately the worst affected area is where the nebulosity is at it's greatest. Do you have any street or security lights that could be the cause of the gradient? I've noticed that on my 130pds light can also enter the OTA from the primary mirror end as well.

I'd also suggest reducing the exposure time & increasing the number of lights, which would make it easier to stack. I tend to shoot at 60sec, but unguided that is pushing it (EQ6). With my Bortle 6 sky I worked out the optimum SNR would be 127 secs for our Canon 600D... but subs of that length will have to wait until I've saved up for a guidescope.

Thanks for making the data available!

Cheers
Ivor

PS: with your set-up  does the focus draw tube extend quite a way into the OTA?

Edited February 29, 2020 by Aramcheck
PS added

[CaptainShiznit]

Cheers for the replies guys, really helpful. To answer some questions, yes the bane of my imaging to the west is a street light overlooking my garden. I suspected it was the culprit of my gradients, although I was imaging brazenly close to it by the time the clouds were approaching. Interesting to see how my LPS filter would size up to it.

3 hours ago, Aramcheck said:

 

PS: with your set-up  does the focus draw tube extend quite a way into the OTA?

I haven't found it to have to be too far into the OTA. I haven't measured but I would say it's still got an inch or more of travel left before it's fully inside.

 

4 hours ago, Aramcheck said:

With my Bortle 6 sky I worked out the optimum SNR would be 127 secs for our Canon 600D.

 

 

Would you mind me asking what your process looked like for working out such an accurate optimum exposure? I would love to replicate it. Cheers!

[Aramcheck]

32 minutes ago, CaptainShiznit said:

Would you mind me asking what your process looked like for working out such an accurate optimum exposure? I would love to replicate it. Cheers!

Thanks @CaptainShiznit

Edited February 29, 2020 by Aramcheck

[Aramcheck]

Sorry - hit the wrong button on the keyboard....

The formula's for the noise calculation are from this talk by Robin Glover (Sharpcap) at last years Practical Astronomy Show: https://youtu.be/3RH93UvP358?t=58

I put them into a spreadsheet (attached).

Street lights are a pain!

Cheers
Ivor

DLSR Noise Calc.xlsx

[CaptainShiznit]

3 hours ago, Aramcheck said:

Sorry - hit the wrong button on the keyboard....

The formula's for the noise calculation are from this talk by Robin Glover (Sharpcap) at last years Practical Astronomy Show: https://youtu.be/3RH93UvP358?t=58

I put them into a spreadsheet (attached).

Street lights are a pain!

Cheers
Ivor

DLSR Noise Calc.xlsx 26.77 kB · 1 download

Brilliant! Thank you

[CaptainShiznit]

4 hours ago, Aramcheck said:

Sorry - hit the wrong button on the keyboard....

The formula's for the noise calculation are from this talk by Robin Glover (Sharpcap) at last years Practical Astronomy Show: https://youtu.be/3RH93UvP358?t=58

I put them into a spreadsheet (attached).

Street lights are a pain!

Cheers
Ivor

DLSR Noise Calc.xlsx 26.77 kB · 3 downloads

Just wanted to say I watched that whole video and it was such an interesting one. I love the scientific and mathematical approach and I think everyone should watch it. One thing that didn't get factored in was the use of a standard light pollution filter though. Any idea how the use of one would affect the optimum sub length? (I have an IDAS D2 for example).

[Aramcheck]

10 hours ago, CaptainShiznit said:

One thing that didn't get factored in was the use of a standard light pollution filter though. Any idea how the use of one would affect the optimum sub length?

I assume it would depend on how much of light is transmitted. In the talk Robin Glover talks about the use of RGB & Narrowband filters requiring longer sub-exposures compared to monochrome, so I would expect the same based on the transmission curve of the filter:- https://youtu.be/3RH93UvP358?t=2904

 

[CaptainShiznit]

29 minutes ago, Aramcheck said:

I assume it would depend on how much of light is transmitted. In the talk Robin Glover talks about the use of RGB & Narrowband filters requiring longer sub-exposures compared to monochrome, so I would expect the same based on the transmission curve of the filter:- https://youtu.be/3RH93UvP358?t=2904

 

I was thinking similar myself. Here's the curve:

So between 400 and 700nm, I can estimate that it's blocking approx 450-460nm (10nm) and 560-630nm (70nm) which means it blocks 80 out of 300nm or 27% of the spectrum. 

Would it be over simplifying to multiply the light pollution electron rate (P) by 0.73 or maybe even just multiplying the exposure time by around 1.37 to compensate? (Hope you follow my maths 😅)

I think I'll try and experiment with both as well as the original exposure time!

[Singlin]

I agree their are alot of gradients and possibly cloud too.Here is my effort with it.