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Final result - as good as it's going to get?

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#1 damarks913

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Posted 19 September 2021 - 04:29 PM

So had 3 hours on M33 last night. First real attempt at OSC. Was on a Skyguider Pro with WO61 and QHY168C. 

 

Used unity gain of 10, offset 50, 60 second subs, 15 flat, 15 dark, 15 dark flats, no bias, using APT.

 

Now the question. Is the attached about as good as it is going to get with this sensor, with the target so relatively small? Or is it more likely:

 

My post processing is still relatively poor?

My settings were off?

Trying this without a filter and the 3/4+ moon?

Combo?

Other?

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#2 jonnybravo0311

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Posted 19 September 2021 - 04:50 PM

Since you didn't mention it, is it safe to assume this was unguided?

 

I think there are a few areas you could try to improve upon here. The first thing to look at is focus. Notice how large the stars are, and how blurry M33 is? These are pretty strong indicators you were out of focus. Unfortunately, there's nothing you can do to fix focus issues in post.

 

The second thing to look at are the star colors. See how virtually every star is completely white? This means you've clipped the highlights. If this was done in post-processing, you can do things like masking out stars to not stretch them so hard. If this was done while capturing the data, this means you need to look at your exposure settings. Try exposures of 30 seconds instead of 60. I don't use APT, so I'm not sure what level of detail is shown when taking subs (like min/max ADU, median, histogram, etc). If you have a histogram, you want it about as close to the left hand side as possible without touching.

 

While we're on colors, notice how the blacks are REALLY black? This is because, like with the highlights, you've clipped your shadows. You've dragged the black point way too far to the right and lost a whole bunch of data.

 

Finally, I'm not sure what filter you were using, but the general recommendation is to _not_ use any light pollution / CLS / L-eN, L-eX, L-Pro filters on broadband targets like galaxies, reflection nebulae, star clusters, etc. The solution is to either a: go to a dark site (which may not be possible) or b: take a lot more total integration time.

 

So, to answer your original question, no, I don't think the image is "about as good as it is going to get with this sensor" :).


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#3 Ken Sturrock

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Posted 19 September 2021 - 04:53 PM

Not a bad picture. You do have some ovalness (elongation) in the stars. Despite the fairly short exposures, the tracking may be off. Assuming unguided? Focus may be a bit soft, although that may be compounded by smear from the tracking. In the grand scheme of things: Three hours isn't a lot of data. More data generally helps the SNR which lets you process it harder without over-doing things but more data also allows you to throw away a lot more frames which are sub-par and still leave enough to get decent SNR. I don't know your software, you might be able to sharpen it and stretch it more but watch the stars, galaxy core and the background is already pretty dark - so tread carefully.


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#4 damarks913

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Posted 19 September 2021 - 05:26 PM

Thank you so much...

 

So much to learn, and yes this was unguided.



#5 dx_ron

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Posted 19 September 2021 - 08:32 PM

APT has some focusing help built in (though I don't use APT so I can't vouch for how well they work). The Z61 has a Bahtinov mask built in to the lens cap, which is always a help in focusing. For unguided imaging you want to get your polar alignment as good as you can, and/or go with shorter exposures.

 

You should be able to take a quite pretty image of M33 with your gear, once you get things dialed in. And spend more time on it - it always comes down to getting more time.


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#6 Sacred Heart

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Posted 19 September 2021 - 09:36 PM

This is a nice picture, beats my first images from years ago.  Focus,  do you have a Bahtinov mask, I made one from foam I got from Hobby Lobby.   Works great, just go to a nearby bright star and focus - straight line in the middle.    Joe

 

Scroll down the page

 

http://www.deepskywa...tinov-mask.html

 

foam I used

 

https://www.hobbylob...-5mm/p/80982129


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#7 matt_astro_tx

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Posted 20 September 2021 - 07:41 AM

That's a great image for a beginner! 

 

I agree it's out of focus.  Spend as much time as it takes getting your focus dead on before taking pictures, because you can't fix it later!  Agree with the recommendation for using a B-mask or some other kind of focusing aid in software.

 

Get out there again and aim for another 3-5 hours (my last galaxy I shot for 12 to really bring out the color) with shorter exposures (30 or 45 seconds perhaps - use the histogram!) and don't stretch it so hard in post processing.

 

You're on your way to a great image.


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#8 damarks913

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Posted 20 September 2021 - 11:10 AM

Thank you all again. I was using the Bahtinov Tool in APT, which said I was in focus, but I agree, in hindsight, obviously, I was not.




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