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Old 21-07-2021, 06:11 PM
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rustigsmed (Russell)
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Planetary imaging small pixels?

Hi all,

At the moment i'm looking at a OSC camera for planetary photography. I already have a qhy163m for mono planetary work and while considered a deep space camera it has yielded excellent results (see attached) using the ROI function in capture programs.

I was am contemplating getting something like a qhy163c or a zwo1600c but the qhy183c has got my attention with its tiny pixels. Yes i know these sensors are bigger than what is "required" but it is nice to have some added flexibility for some mid size sensor DSO or comets.

Do people have any particular views on the smaller pixels for planetary? is it likely not going to make a difference due to the extreme over sampling already at f25 (I usually image 12" f5 but with a 5x powermate)? But what if there is some moments of crystal clear seeing (optimistic i know)?

I'm not sure it has been discussed too much before in relation to planetary astro. Interested in your views.

Just a heads up i was looking at doing an animation for Jupiter 9th Sept - check it out in stellarium its going to be epic.

Thanks

Rusty
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Old 22-07-2021, 07:36 PM
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Russell, one of the reasons planetary imagers usually choose the cameras they do is signal to noise ratio. The IMX224, IMX290 and IMX462 are the accessible (mainstream) leaders on that front.

These cameras also support very high frame rates when using ROI, which helps maximise the chances of snapshotting good moments.

The IMX183 isn’t quite in the same ballpark as the above when it comes down to it. I have a 183C and the frame rates, even with a small ROI, just aren’t up there. I love it as a deep sky camera though, and it’s fun to chase the Moon with it too.

It is worth optimising your optical train to match your pixels, as you’ll get better signal in that sweet spot. So just consider that the camera and suitable multiplier go together as a combo, for best results.
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Old 22-07-2021, 11:15 PM
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Rerouter (Ryan)
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Sweet spot for planets is
Pixel size (microns) = F/Ratio / 1.8

That is the dawes limit for detail e.g. almost 0% contrast between adjacent pixels, any less and its not going to pull out enough detail for registax to work its magic without a lot of frames, much larger than / 1.5 and your getting less detail than you could.
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Old 23-07-2021, 07:44 AM
Startrek (Martin)
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Russell,
I mostly image DSO’s with my cooled 2600MC but dabble in a bit of planetary imaging from year to year using my old Canon 600D my after following Jerry Lodriguss in the US about 5 years ago
You can just about use anything to do planetary but obviously 2 key factors are atmospheric seeing conditions and focal ratio
His general rule of thumb for planetary imaging is -
General rule of thumb to determine the “best focal ratio” of your image train for Lunar and Planetary imaging is -
Poor night of seeing 3.5 x pixel size of your camera
Average night of seeing 5 x pixel size of your camera
Good night of seeing 7 x pixel size of your camera

My old Canon has a pixel size of 4.3uM so on nights of average seeing I use a focal ratio close to f21 and nights of good seeing around f30

Here’s my images of Saturn and Jupiter captured last year on a night of average to good seeing using my 6” f6 GSO newt ( OTA cost me $299 ) and my 11 year old Canon 600D using a 4 x Powermate to achieve enough focal length for the required focal ratio

I’m using basic low end equipment ( beginners equipment) but you can still manage respectable planetary images using the above general rule of thumb and night of good seeing

Video data ( 1500 Avi frames ) was captured with BYEOS, stacked in Autostakkert 3 and sharpened etc... in Registax 6

Cheers
Martin
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Old 23-07-2021, 12:35 PM
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thanks dunk, ryan and martin.

how slow are we talking for the 183c Dunk? Was that in 8bit mode? that sounds like the main issue you have with it in terms of planetary? It is a very sensitive camera still so i'm not sure the SNR is going to be a major issue for it. The pixel size on the other sensors are also small < 3 microns but more than 2.4 of the 183c. So in essence small pixels are on the good dedicated planetary cams.

Ryan the formula you've put down seems to suggest that quite large pixels are suitable which is interesting. so most cameras are already over sampling quite a lot so perhaps no massive benefit in going extra small.

cheers martin - looks like a good rule of thumb for adapting to the seeing conditions.
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Old 23-07-2021, 12:48 PM
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Yeah, I've spent a lot of time reversing out what conditions a lot of the rules of thumb fall under, most of it I put together for lucky imaging, but it still has the same limits of physics as planetary.

Where lots of frames can help is it effectivly does "superresolution" e.g. pixels moved a fraction of there width, and can technically allow them to act as if they are larger pixels, but it still needs dynamic range to make that process possible at the end, so your generally just making the image bigger, but not more detailed past certain limits

/ 3.14 = Dynamic Range Limit (No amount of subs will help)
/ 1.80 = ~0% contrast (Dawes Limit - Stacking Detail)
/ 1.48 = 9% contrast (Rayleighs Limit - Single Sub Detail)
/ 0.68 = 50% contrast (MTF50 - Apparent Sharpness)
/ 0.29 = 80% contrast (MTF80 - Imaging Times)

Last edited by Rerouter; 23-07-2021 at 08:27 PM.
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Old 23-07-2021, 03:42 PM
Startrek (Martin)
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Quote:
Originally Posted by Rerouter View Post
Yeah, I've spent a lot of time reversing out what conditions a lot of the rules of thumb fall under, most of it I put together for lucky imaging, but it still has the same limits of physics as planetary.

Where lots of frames can help is it effectivly does "superresolution" e.g. pixels moved a fraction of there width, and can technically allow them to act as if they are larger pixels, but it still needs contrast to make that process possible at the end, so your generally just making the image bigger, but not more detailed past dawes limit.
/ 1.80 = 0% contrast (Dawes Limit - Stacking Detail)
/ 1.48 = 9% contrast (Rayleighs Limit - Single Sub Detail)
/ 0.68 = 50% contrast (MTF50 - Apparent Sharpness)
/ 0.29 = 80% contrast (MTF80 - Imaging Times)
Ryan,
Do you have any of your planetary images to compare and demonstrate the details of your findings above ?
I’m most interested
Cheers
Martin
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Old 24-07-2021, 12:24 PM
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Quote:
Originally Posted by rustigsmed View Post
thanks dunk, ryan and martin.

how slow are we talking for the 183c Dunk? Was that in 8bit mode? that sounds like the main issue you have with it in terms of planetary? It is a very sensitive camera still so i'm not sure the SNR is going to be a major issue for it. The pixel size on the other sensors are also small < 3 microns but more than 2.4 of the 183c. So in essence small pixels are on the good dedicated planetary cams.
All in 8-bit mode:
800x600 => 80fps
640x480 => 100fps
480x352 => 133fps

So it's important to calculate the minimum ROI you need to squeeze the best out of it.

The 224, 290 and 462 benefit from the HCG (high conversion gain) mode which gives them super low read noise (as little as 1/3) and the 183 just can't compete with that.

There are a lot of posts about using:

optimal_f_ratio = pixel_size(in microns) x 5

(but I don't have the references to hand right now)

So it's worth bearing all that in mind when picking a camera for planetary.

FWIW, I've tried my 183 with my C11 and it's a bit weak on anything besides the Moon, in comparison to the others mentioned above.
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Old 24-07-2021, 12:30 PM
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Note: several ZWO cameras, including some of the planetary cams, are currently reduced as part of ZWO's summer sale
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Old 24-07-2021, 04:41 PM
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billdan (Bill)
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Russell,

You are restricted by the Dawes Limit of the mirror, as to how much resolution you can achieve by lucky imaging.

D.L = 120arcsecs / Aperture(mm) For your mirror it is 0.4arcsecs.

Sampling rate is 206.3 x Pixel size / Focal Length (assuming 3 micron px)

At F5 your sampling at 0.41arcsec/px (= to Dawes limit)
At F15 your sampling at 0.13arcsec/px (3 times Dawes limit)
At F25 your sampling at 0.08arcsec/px (5 times Dawes limit)

For imaging the experts say we should be sampling at 3 times our required resolution.
You would be OK at F15 and I don't think the 183 cam will show any difference in resolution to your 1600.
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Old 27-07-2021, 03:21 PM
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rustigsmed (Russell)
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thanks everyone for your replies - I appreciate it.

still a bit undecided on where to spend the money i think I want a larger sized osc cmos and a planetary cam which i could do with a qhy183c or 163c or 2600mc but I would just lose out on some fps not that they are slouches and more than capable of producing excellent planetary images just that something like a zwo224mc can do about 2-3x as many fps and probably result in some better images in average seeing.

thanks
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