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How better equippment improved my imaging: M33 comparison

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#1 the Elf

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Posted 06 December 2018 - 03:15 AM

Hello all,

 

"you get what you pay for" is written so often at CN. Well, what does this actually mean in terms of image quality?

Here is an animated gif, cropped and downsampled to stay within the upload limit and well aware of gif's quality limits but a good way to demonstrate the improvment:

 

M33-compare.gif

 

... (upload limit) ....


Edited by the Elf, 06 December 2018 - 03:30 AM.

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#2 the Elf

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Posted 06 December 2018 - 03:22 AM

...

Crops of the above scaled down to approx. half resolution:

 

Jan50C.jpg dez50C.jpg

 

The two images are:

Jan 2018: GSO RC6, TS-CCD47 reducer, stock Canon 600D(=T3i) resulting in 1.1arcsec/pix, Celestron AVX, SL50D guide scope w. ZWO ASI 120MM, PHD2, 12x5min, FWHM 5.4...6.5 arcsec

Dez 2018: GSO RC8 carbon, TS-CCD47 reducer, same camera resulting in 0,85arcsec/pix, Skywatcher EQ6-R, ZWO OAG, Lacerta MGEN-II, 34x3min, FWHM 3.4...5.1 arcsec (clouds in some subs)

Processing in PI, though my processing skills might have improved I guess processing has little impact. Both scopes were collimated without any special tools just by creating a concentric look and a final fine tuinig with a bright star.

I expect the current image to become much better as soon as the weather allows to take some clear L with my mono. Here I intentionally compare OSC to OSC to point out the difference of scope, mount and guiding. It is pretty clear that using luminance subs and adding more data yields a better image.

 

So, I hope it helps someone who is seeking a setup. My conclusions:

- buy a mount in the EQ6-class, don't go for AVX/EQ5

- the small RCs need OAG to deal with the moving rear cell. The RC6 suffer from it a lot, I can't tell how much better the RC8 is as I never tried guiding it with a guidscope and always use OAG

- there is a difference in resolution between the 6'' and 8''version of the same design that is just below / above decency level in my eyes. I have a feeling like the quality of the RC8 is better in general and the better resolution is not only the physical limit but also optical quality of the mirrors.

 

clear skies!

the Elf


Edited by the Elf, 06 December 2018 - 03:31 AM.

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#3 james7ca

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Posted 06 December 2018 - 04:32 AM

That's an interesting comparison, but how can you be sure that all of the difference is being caused by the equipment? You might have achieved better focus when making the most recent image and in any case differences in the seeing conditions could have easily caused most or all of the changes in resolution. On a good night I can often get FWHM measurements down below 2 arc seconds in luminance with my 5" refractor and then a few days later I'll be up to 5 arc seconds just because of a difference in the seeing conditions.

 

Probably the only way you could know for sure is to image side-by-side on the same evening and after checking and rechecking the focus and collimation on each system. That said, better equipment can result in better results, so you probably are getting some benefits with your latest setup.



#4 einarin

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Posted 06 December 2018 - 08:45 AM

Can see better tracking and focus in second image.



#5 happylimpet

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Posted 06 December 2018 - 09:22 AM

Yeah, I wouldnt be at all surprised if thats just down to seeing and/or focus. Though as Einarin says the guiding does look suspect in the 'before' image.



#6 vio

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Posted 06 December 2018 - 09:25 AM

Thanks for the side by side comparison, quite interesting.
Yet, I’m not sure what to make of it. The differences in focus and especially the exposure at 60 vs 102 minutes may have more to do with the results. Also, the shorter subs (3min vs 5min) could help in getting better results.


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#7 mantrain

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Posted 06 December 2018 - 11:14 AM

So people cannot get good resolution using an AVX?  



#8 the Elf

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Posted 06 December 2018 - 11:52 AM

 

but how can you be sure that all of the difference is being caused by the equipment?

I know from using the RC6 on the AVX for 1.5 years, focussing with a bathinov mask. All images, no matter what season or object looked the same plus elongated stars. The elongation is gone since I use the OAG. Now I have the RC8 since half a year and no matter what the weather is like or what objects there was more resolution. The images shown are just an example of what I see all the time. I have some objects imaged with both systems and the trend is the same.

 

So people cannot get good resolution using an AVX?

When using it at medium dec, not too close to the zenit and when guiding at a short leash and without wind the resolution is similar, but the number of limitations is too much for me. I'd like to image in the zenith and with little wind as well. And I like to have the object in the center of the image after a goto command.

 

The differences in focus and especially the exposure at 60 vs 102 minutes may have more to do with the results

Here is an image with almost 7h RC6 on AVX. Still there is a resolution limit.

https://www.astrobin...355156/?nc=user

This is the same object taken with the RC8 by the previous owner who is an a far higher skill level, taken about 150km west from my location.

https://www.astrobin...4179/B/?nc=user

Sorry, again the better one is exposured longer, but this is the best I could find.

 

I'd be glad to do a more scientific comparion like putting both setups side by side but right now I don't have all parts to run them both and I'm just happy with what I got and try to sell the old stuff (which does not work for some reason. Anyone in Germany who wants it?)


Edited by the Elf, 06 December 2018 - 11:55 AM.


#9 Merk

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Posted 06 December 2018 - 12:46 PM

Well I have to say that the thing the makes a big difference of the 2 pictures is the OAG. 

 

When I first guided my 120 Esprit with OAG I saw a big difference in image quality, stars are pin point and faint details are sharper. 


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#10 Stelios

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Posted 06 December 2018 - 12:47 PM

So people cannot get good resolution using an AVX?  

Depends on the actual AVX, but overall it will be far more challenging than it would be with a better mount, unless the AVX is good and the payload is quite light. 

 

Also (for good AVX's--meaning ones that don't have random DEC excursions) an OAG helps enormously. On my replacement AVX I was able to get 0.82" RMS with an OAG in low wind, whereas the best I'd ever done was around 1.2" with a guidescope. But you need to be careful with balancing and PhD2 settings. 

 

So it's possible (with asterisks). But if one is going to be seriously involved with the hobby, he's going to waste so much time that upgrading the mount would be a no-brainer, even if he works at low pay for the hours it would save him.



#11 james7ca

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Posted 06 December 2018 - 07:53 PM


...but how can you be sure that all of the difference is being caused by the equipment?

I know from using the RC6 on the AVX for 1.5 years, focussing with a bathinov mask. All images, no matter what season or object looked the same plus elongated stars. The elongation is gone since I use the OAG. Now I have the RC8 since half a year and no matter what the weather is like or what objects there was more resolution. The images shown are just an example of what I see all the time. I have some objects imaged with both systems and the trend is the same...

That seems a fair analysis and it provides additional information over your original post.



#12 the Elf

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Posted 07 December 2018 - 02:07 AM

Yep, I should have added this to the original post.




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