First astro camera - 269 or 294 sensor - sampling confusion

[vlaiv]

1 minute ago, Adam J said:

Probably need to sharpen the original to compare then. 

Actual comparison would be to take linear data, but in any case - it shows two very important things:

- you are a bit over sampled on that image - probably not 2"/px, but not as high as 1.4"/px either (we can't really tell without actual FWHM measurement).

- differences are very small when things get this sharp (and it is indeed sharp image).

Way image is processed will have more impact than difference of 1.8"/px vs 1.4"/px if data is handled properly.

[Adam J]

16 minutes ago, vlaiv said:

Check that left against original.

(hint - I think I left sharpen when resampling turned on )

Actually looking at my original I would say neither image fully matches it. Is something else going on when you put the side by side in your software? My point of comparison for blinking is the small satalite galaxy to the lower left of NGC4565.

 

Wondering if somehow this has undergone a double hit of JPG compression? It is worth noting that the TIF of this looks better. 

Edited February 7, 2022 by Adam J

[Adam J]

But to bring it back onto topic I would say that the conclusion for me is get the IMX533, because: 1) Its back illuminated and the 269 is not, 2) You really dont need to go to 3.3um pixels as per the above discussion, 3) Although the 294 is perhaps the best match to a longer focal length refractor 700mm or so, I dont like the way many have issues with calibration when using duel narrow band filters. 4) The OP says he wants to image smaller targets, so the size difference between the two sensors is probably not a factor. 

 

Actually ill amend that and say get the 533 mono when it comes out lol. That way you can get a smaller scope for the same sampling, but OP may not like the idea of mono...., 

Edited February 7, 2022 by Adam J

[vlaiv]

1 hour ago, Adam J said:

Wondering if somehow this has undergone a double hit of JPG compression? It is worth noting that the TIF of this looks better. 

Could be that SGL recompresses it upon upload and it could be that jpeg has something to do with it.

[900SL]

I literally ordered the 533MC Pro ten minutes ago from FLO now they have some in stock. 

This will suit me for several reasons. I have wide field lenses and scopes (135SY, 180FMA, GT71) so will give a narrower FOV for my favourite targets, the square sensor and size will be more tolerant of any edge of frame and field flatness or tilt issues, the sensor seems pretty good with zero amp glow and decent specifications, and I think it's a good first dedicated astro camera after my DSLRs

[Milesy303]

21 hours ago, vlaiv said:

I worry about that all the time

Do you have any idea of what sort of working resolution you want to achieve?

Hi @vlaiv - I will be honest I am not sure exactly how to answer. When I said resolution I just implied the only resolution I know is what I have had with my DSLR.

I want to go to a longer focal length to get better shots of things like the pinwheel, bodes, owl nebula etc I have managed to get a lot of these already, but require big crops, and then lots of processing. noise reduction and deconvolution etc. 

Now I just want to be able to produce better pictures and move onto the next stage of my journey 

Chris 

[Milesy303]

On 07/02/2022 at 17:35, Adam J said:

But to bring it back onto topic I would say that the conclusion for me is get the IMX533, because: 1) Its back illuminated and the 269 is not, 2) You really dont need to go to 3.3um pixels as per the above discussion, 3) Although the 294 is perhaps the best match to a longer focal length refractor 700mm or so, I dont like the way many have issues with calibration when using duel narrow band filters. 4) The OP says he wants to image smaller targets, so the size difference between the two sensors is probably not a factor. 

 

Actually ill amend that and say get the 533 mono when it comes out lol. That way you can get a smaller scope for the same sampling, but OP may not like the idea of mono...., 

Mono I like in theory but I’m limited in budget and can only afford a camera just now. So I invest in a camera and don’t use it until i have the filters and wheel and eaf, and by the time next season comes and I unbox there will be a new camera I wish I had invested in. 

Or I just bank the money and write off the rest of the season and don’t do any imaging. End up with car troubles or my boiler breaks and I need to spend the money and in one years time I’ll be back writing the same post again haha  

So really I don’t want to hold off and just make the best purchase I can, even if it’s not best paired with my scope for a few months and then after the summer I’ll get a longer focal length. I don’t plan on staying with the GT81 so I don’t want to match it  

 

 

[drjolo]

Hi Chris,

Just a bit from my past - I started to image with 6" newton and modded Canon 20D, and then realized that I was very much interested in galaxies. I switched to CCD mono camera with small sensor (Atik314) and used just L filter at the beginning, and I was extremely happy with these monochromatic frames. After some time I invested in filters and manual wheel, and was able to pick color images as well.

The sensitivity boost you get with mono sensor compared to OSC version is quite significant, so if you can live with BW images for a while, you may consider this approach. 

Edited February 9, 2022 by drjolo

[vlaiv]

On 08/02/2022 at 10:44, Milesy303 said:

Hi @vlaiv - I will be honest I am not sure exactly how to answer. When I said resolution I just implied the only resolution I know is what I have had with my DSLR.

I want to go to a longer focal length to get better shots of things like the pinwheel, bodes, owl nebula etc I have managed to get a lot of these already, but require big crops, and then lots of processing. noise reduction and deconvolution etc. 

Now I just want to be able to produce better pictures and move onto the next stage of my journey 

Chris 

Here is the thing - you can't zoom in indefinitely as there is limit imposed by optics, atmosphere and mount.

Most galaxies are smaller than M101 you imaged and that one is 22 arc minutes in diameter.

With something like 1"/px - being absolute maximum in realistic resolution in amateur conditions - that would make M101 be 22 * 60 / 1"/px = 1320px

Even at max zoom level (if you are able to image at that resolution and still make sharp image) - you will need to crop your sensor if you are using something like DSLR with ~5000px in width.

I would say that good working resolution until you really hone your imaging / technical skills is about 1.5"/px - that would make M101 - only 880px in diameter.

Not sure if that would satisfy you (it is about x4 more zoomed in than above image of M101 you posted - but I guess that one was resized down).

To realistically get 1.5"/px - you will need 6" of aperture and depending on selected camera - different focal lengths:

3.3um pixel size - 900mm of focal length with super pixel debayering

3.75um pixel size - 500mm of focal length (that would make setup ~F/3.2 - so not really option), or 1000mm with super pixel debayering

4.65um pixel size - 650mm of focal length (in this case - maybe go with 130pds?) or fast F/4 150mm newtonian. Alternative is to go with F/8-F/9 150mm scope for ~1300mm of focal length and use super pixel debayering.

If aiming for this resolution with smaller scope - I would choose F/9 RC scope + 294 camera. Big warning - people have trouble collimating these scopes and many have given up on them. It is not easy instrument to work with for some people. Camera is also sensitive on calibration - most notably flat frames. I've seen many people report problems if they use flat assistant on APT. There were also thread about this camera saturating "early" - around 50000ADU with some gain settings - which again causes problems with flats if one is not mindful about that (and things that standard 65K is saturation point).

 

[Adam J]

1 hour ago, vlaiv said:

 

If aiming for this resolution with smaller scope - I would choose F/9 RC scope + 294 camera. Big warning - people have trouble collimating these scopes and many have given up on them. It is not easy instrument to work with for some people. Camera is also sensitive on calibration - most notably flat frames. I've seen many people report problems if they use flat assistant on APT. There were also thread about this camera saturating "early" - around 50000ADU with some gain settings - which again causes problems with flats if one is not mindful about that (and things that standard 65K is saturation point).

 

Its worse than that, in addition to the early saturation there is evidence its non linear for gains between 120 and 190 and that really messes with calibration. A friend has recently had more success with flats at gain 200. 

Adam 

Edited February 9, 2022 by Adam J

[vlaiv]

22 minutes ago, Adam J said:

Its worse than that, in addition to the early saturation there is evidence its non linear for gains between 120 and 190 and that really messes with calibration. A friend has recently had more success with flats at gain 200. 

Adam 

Is this affecting all ASI294mc-pros or just some?

Could it be bug in drivers or something? I've seen many people do just fine with these cameras, and 120-190 gain range is the best one, so probably a lot of people will be using it.

[Adam J]

6 minutes ago, vlaiv said:

Is this affecting all ASI294mc-pros or just some?

Could it be bug in drivers or something? I've seen many people do just fine with these cameras, and 120-190 gain range is the best one, so probably a lot of people will be using it.

I have seen it effecting many 294 cameras, its caused by a combination of a fixed pattern that changes from camera to camera and can be variable in severity and the slight none linearity of the sensor in that gain window. Also if you have sufficient LP then you can swamp the issue. 

Extensive discussion around this on cloudy nights and some on the sharp-cap forums. But yes some will see it more than others, always something there and you can removed it with skilled use of a dynamic background extraction. 

The effect is most obvious when the camera is used with Narrow band filters. 

Adam

Edited February 9, 2022 by Adam J

[Laurin Dave]

Also some discussion of the flats issue on the ZWO forum ASI294 MM-Pro flat field question - ZWO User Forum (astronomy-imaging-camera.com)   

Dave

[Adam J]

41 minutes ago, Laurin Dave said:

Also some discussion of the flats issue on the ZWO forum ASI294 MM-Pro flat field question - ZWO User Forum (astronomy-imaging-camera.com)   

Dave

I think the reason for the pattern and the reason why its not calibrating correctly are two different issues. The pattern means that calibration errors are very apparent but the pattern in itself is not the cause of the calibration errors, the cause of the calibration errors is non-linearity of the sensor response with exposure. and failure of the sensor to fully saturate at specific gains. 

Maybe @PadrePeace can comment on the results at Gain 200 in comparison to gain 121. 

Adam

[vlaiv]

By the way - is this the same for both OSC and Mono sensor?

[Adam J]

31 minutes ago, vlaiv said:

By the way - is this the same for both OSC and Mono sensor?

The pattern is certainly present on the mono version and I don't see why it would be different in terms of linearity / saturation. 

What i would say is that it was odd that Sony gave the mono version of the IMX294 a new designation IMX492, see what they did there as opposed to every other chip they make which retains the IMX designation from OSC to mono.....so perhaps something else was tweaked apart from removing the Bayer matrix?

As the issue is worst in duel narrow band filters it may not be as heavily reported as you would not use such a filter on a mono camera. But then again those who have used a pure Ha filter on a OSC 294 have reported calibration issues. 

Personally I have determined that I wont be spending £1500 to find out first hand for myself. 

https://www.cloudynights.com/topic/762898-mottling-in-asi294mm-image-and-flats/page-2

Adam 

Edited February 9, 2022 by Adam J

[Milesy303]

On 09/02/2022 at 12:39, vlaiv said:

Here is the thing - you can't zoom in indefinitely as there is limit imposed by optics, atmosphere and mount.

Most galaxies are smaller than M101 you imaged and that one is 22 arc minutes in diameter.

With something like 1"/px - being absolute maximum in realistic resolution in amateur conditions - that would make M101 be 22 * 60 / 1"/px = 1320px

Even at max zoom level (if you are able to image at that resolution and still make sharp image) - you will need to crop your sensor if you are using something like DSLR with ~5000px in width.

I would say that good working resolution until you really hone your imaging / technical skills is about 1.5"/px - that would make M101 - only 880px in diameter.

Not sure if that would satisfy you (it is about x4 more zoomed in than above image of M101 you posted - but I guess that one was resized down).

To realistically get 1.5"/px - you will need 6" of aperture and depending on selected camera - different focal lengths:

3.3um pixel size - 900mm of focal length with super pixel debayering

3.75um pixel size - 500mm of focal length (that would make setup ~F/3.2 - so not really option), or 1000mm with super pixel debayering

4.65um pixel size - 650mm of focal length (in this case - maybe go with 130pds?) or fast F/4 150mm newtonian. Alternative is to go with F/8-F/9 150mm scope for ~1300mm of focal length and use super pixel debayering.

If aiming for this resolution with smaller scope - I would choose F/9 RC scope + 294 camera. Big warning - people have trouble collimating these scopes and many have given up on them. It is not easy instrument to work with for some people. Camera is also sensitive on calibration - most notably flat frames. I've seen many people report problems if they use flat assistant on APT. There were also thread about this camera saturating "early" - around 50000ADU with some gain settings - which again causes problems with flats if one is not mindful about that (and things that standard 65K is saturation point).

 

Thank you for all the great advice @vlaiv - I went a step further and chose the 115M camera, which by all I read is the mono version of the 294.

I have created a new thread for some advice on filters and mounting them.

Thank you to everyone else to helped me make a decision, it is much appreciated.

[AstroGS]

I’ve got a WO GT81 with flattener 6AIII, on a SW AZ-EQ5 and recently bought the ASI533MC.

 

Here is what a single 600 secs look like from this setup + an Optolong L-Extreme.

 

 

[Adam J]

On 07/02/2022 at 10:15, Milesy303 said:

Hi all.

I’m currently looking at both sensors to use with my GT81 scope for a few months but want to go to a longer focal length for after the summer. I have been looking at the same targets at the same resolution for quite a few years with my DSLR and my primary objective is getting into smaller targets and more detail.

With the 269 I’ll be over sampled when I go to the longer focal length but there is no amp glow to deal with.

The 294 seems an older technology but maybe bet better suited to upgrading after the summer ?

To be used under "uk seeing" which I think might be "ok"

My head hurts with all the sampling and seeing.

 

Chris

UK seeing is not ok in my experience. 

I know people that make the 294 work but its can be a pain to calibrate and some people seem to never get it to work for them. 

In all honesty I think that the only OSC options I would consider are the 533 and the 2600 (but probably the rising cam version of the 2600 (IMX571)).

 

Adam