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Es 127 ed Apo /zwo camera suitability?

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#1 Stargazing)

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Posted 26 September 2021 - 05:26 PM

Hi,
Can u help me chose between zwo 294mm pro and zwo 183mm pro for my Explore scientific 127ed.
I have been checking their compatibility with the scope using the following link
https://astronomy.to...ccd_suitability
I have been getting significant under sampling with the 294mm pro..I know i can unlock the bin1 and will change the pixels to 2.3um for a good seeing, whereas the 183mm pro is already at 2.4um.
Any feedback or suggestions are appreciated.
Clear skies

#2 maximalz

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Posted 26 September 2021 - 06:06 PM

I do believe the 294MM Pro, in general and without looking at your particular scenario, is the better camera.

 

  • It is newer, has 14 bits of depth (VS 12 for the 183MM) in 2x2 bin mode, which pretty much means it sees slight differences better
  • has a MUCH larger full well (66k e- VS 15k e- for the 183MM), which means you have more room for every pixel before it gets fully saturated (= 100% white)
  • Peak QE slightly above the 183MM (so slightly more signal efficient basically)

 

Now, regarding your situation, I'd say that if you are being slightly under or oversampled, you'll hardly notice the difference, as there are many variables coming into play with this. From this article, it says that being undersampled is a pain for stars shapes, which you can manipulate a lot with post processing (Deconvolution and Drizzle techniques come to mind here). Whereas with oversampling you're kind of getting a bloated image, and generally something that effects the whole picture : you simply need more signal to noise.

 

One thing of importance too, if you're using a refractor telescope which the ES 127ED is, you're most likely using a field flattener: do you own or plan to own a field flattener? Is it a focal reducer at the same time? Because this is important: if using a 0.8x focal reducer, you're smack in the middle of a good sampling in 1x1 bin mode, but seriously under-sampled in 2x2. If owning a field flattener and flattener only, you'll be slightly undersampled in 2x2 and great in 1x1. All under average seeing (the one you're most likely to see the most often).

 

Anyway, all in all I tend to prefer the 294MM Pro, both in general and in your situation.

 

Please do keep in mind that I'm not currently in that situation and I might miss some first hand experience regarding this, so don't base your decision solely on my post!


Edited by maximalz, 26 September 2021 - 06:07 PM.

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#3 bobzeq25

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Posted 26 September 2021 - 06:15 PM

The scope has a focal length of 952mm, correct?  And is F7.5?

 

I have both 183s.  I got them for my C8 RASA, 400mm, F2.  That's the sweet spot for the 183, short fast optics.  Image scale is about 1.2.  Sample image, 2 frame mosaic of M31.  750X10" total. Short subs to reduce clipping (as the tiny wells filled).

 

https://www.astrobin.com/025umc/

 

I tried it with my TS Optics 130mm, F7.  Image scale was about 0.6.  That's significantly oversampled in even very good seeing.  Results were unattractive, poor snr, one of my least liked images on astrobin.  I've removed it.

 

The 294 mm bin 2 yields an image scale of just about 1.0 with the 127.  I would in no way consider that as "significantly undersampled", in any skies.

 

In my view the 183 is a niche camera, and its niche is short fast optics.  The tiny pixels are both snr challenged, and dynamic range challenged.  With that scope, you'd need long total imaging times, to improve snr, and _many_ subexposures, to avoid clipping.


Edited by bobzeq25, 26 September 2021 - 06:29 PM.

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#4 jonnybravo0311

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Posted 26 September 2021 - 08:44 PM

Hi,
Can u help me chose between zwo 294mm pro and zwo 183mm pro for my Explore scientific 127ed.
I have been checking their compatibility with the scope using the following link
https://astronomy.to...ccd_suitability
I have been getting significant under sampling with the 294mm pro..I know i can unlock the bin1 and will change the pixels to 2.3um for a good seeing, whereas the 183mm pro is already at 2.4um.
Any feedback or suggestions are appreciated.
Clear skies

I'm not sure where you're getting that the 294 and 127 results in "significant under sampling". That image scale in the default bin2 mode gives you a 1"/px image resolution. Unless you live on top of a very high mountain in Chile where the seeing is perfect, 1"/px is a very good image scale.

 

As an owner of the 294MM Pro, one of the reasons I purchased the camera was for its dual nature. With my setup, I get a 2.5"/px image scale running it in the default mode and 1.25" running it unlocked. I use both modes regularly. The native (unlocked) mode basically gives you a 183MM with a better, larger sensor. However, with that ED127 scope, you're very likely going to be sticking to the default (bin2) mode.

 

The one caveat to the 294 is that it is rather finicky when it comes to calibration. You _need_ to take and use calibration frames. There is no getting away without them. Also, you don't use bias frames. You calibrate your flats with dark flats. However, once you get that calibration process down, the 294 can make some fantastic images, IMHO.


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#5 Stargazing)

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Posted 27 September 2021 - 05:38 AM

Thank you all for your replies.. I appreciate it.
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