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Eta Carina NB - comparing two setups

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#1 Henry from NZ

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Posted 30 June 2020 - 05:10 AM

I have recently tested new gear by imaging again the Eta Carina nebula -- a bright convenient target where I am as it is circumpolar. As usual I like light-handed processing e.g. DBE, crop, minor de-noise, stretch and color curves. No de-convolution or other complicated stuff.

 

So did the finer pixel scale of 1.15 arc-sec / px bring any improvement? Your views welcome...

 

Latest image - 183 camera using a 430 mm FL newtonian 1.15 arcsec per px, FOV 106 arc-min x 71 arc min:

https://flic.kr/p/2jgK6rD

 

Previous image - 460 camera using a 246 mm FL refractor 3.8 arc-sec per px, FOV 174 arc-min x 139 arc-min:

https://flic.kr/p/Taa7Qb


Edited by Henry from NZ, 30 June 2020 - 05:13 AM.

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#2 Dunkstar

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Posted 30 June 2020 - 05:24 AM

The finer pixel scale results in finer details being visible - as you’d expect.

 

Surely you can see that for yourself ;)



#3 Tapio

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Posted 30 June 2020 - 05:33 AM

What is/was your 246 mm FL refractor ?



#4 ZL4PLM

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Posted 30 June 2020 - 05:33 AM

But you can drizzle and easy improve the larger pixel scale which is a simple improvement



#5 imtl

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Posted 30 June 2020 - 05:52 AM

But you can drizzle and easy improve the larger pixel scale which is a simple improvement

With a deterioration of SNR. So improvement is relative.



#6 Henry from NZ

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Posted 30 June 2020 - 05:55 AM

246 mm refractor = FS60 with reducer at around f/4.

 

I have used the Atik460 for many years and I have recently purchased a second hand 183 camera because I want to have finer pixel scale.

 

However so far I have not realised the theoretical benefit that the new camera should bring.

 

I should note that the above examples are probably not fair comparison as the focal lengths of the OTAs are different. When using the same OTA the differences are not as obvious -- for example, this image of the Running Chicken nebula was taken with the newt and 460 and compared to the Eta Carina image using the same OTA and 183 camera the difference is not so obvious any more:

 

https://flic.kr/p/TD6wkh

 

My original plan was to sell the 460 once the 183 is up and running and use the proceed towards a bigger sensor camera. However after testing I think overall I still prefer the 460 (its easier to use for arguably similar result). But then I am not sure whether this is user error and I don't want to give up on the 183 just yet.


Edited by Henry from NZ, 30 June 2020 - 06:07 AM.


#7 Dunkstar

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Posted 30 June 2020 - 06:12 AM

A 60mm refractor doesn’t have the theoretical resolution to really make a huge difference between those two cameras...especially if the seeing is questionable.

 

I’ve taken shots of Eta Carinae and Centaurus A and it can be difficult to spot the difference between those from a 183 and a 1600...complicated - or should that be convoluted? - by the seeing differences across different nights. I’d not dare change the camera on the newt after sunset lol.gif


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#8 ZL4PLM

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Posted 30 June 2020 - 06:22 PM

With a deterioration of SNR. So improvement is relative.

you don't loose SNR if you have enough data and on low numbers of subs it still helps if your very undersampled- you're putting data back in not loosing it which improves resolution and sharpness in the overall image too .

 

noise at best remains the same - for example splitting noise from 1 px over 2 x 2 spreads the noise over wider space but you also spread the signal over the same - so at best case its net gain/loss - personally I have not seen massive losses in SNR on drizzle data but what you do win on is sharpness - better resolution on high pixel scale images like this and in my experience it really helps when processing - drizzle really helps the core pix processes work well - so def find on refractors with high pixel scales like this its almost a must

 

So I disagree its relative - its far more 

 

Cheers

 

Simon 


Edited by ZL4PLM, 30 June 2020 - 06:50 PM.


#9 Henry from NZ

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Posted 02 July 2020 - 07:39 PM

It is difficult trade off as I like muredenoise which means that drizzle cannot be used.
Anyway I will likely try the small pixel camera some more and do some more comparison before deciding where I will go from here. It is not like there is any affordable alternative except the 1600 which I do not like.

The 6200 would have been ideal on paper but too costly at the moment.

#10 imtl

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Posted 02 July 2020 - 09:44 PM

you don't loose SNR if you have enough data and on low numbers of subs it still helps if your very undersampled- you're putting data back in not loosing it which improves resolution and sharpness in the overall image too .

 

noise at best remains the same - for example splitting noise from 1 px over 2 x 2 spreads the noise over wider space but you also spread the signal over the same - so at best case its net gain/loss - personally I have not seen massive losses in SNR on drizzle data but what you do win on is sharpness - better resolution on high pixel scale images like this and in my experience it really helps when processing - drizzle really helps the core pix processes work well - so def find on refractors with high pixel scales like this its almost a must

 

So I disagree its relative - its far more 

 

Cheers

 

Simon 

So you agree that the upper limit is to keep the same SNR and it requires very specific conditions as I marked them in your reply. Which means that in most cases you loose SNR. I agree that loosing some while gaining resolution is a good thing sometimes. 

Eyal



#11 sunnyday

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Posted 02 July 2020 - 10:05 PM

both are very pretty, but I prefer the first.
for details.
thanks.




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