Best sized pixels for EAA

[Mike JW]

Probably a naive question. For EAA  and going after DSOs is it better to have larger or smaller pixel size. I go round and round in circles trying to make sense of the technical info.

Currently have an Ultrastar mono. Looking to buy a second camera -ZWO ASI 174 or the Altair 174 Mon , both with 5.86 pixel size but then I think should I get a camera with much smaller pixels eg  ZWO 224 or Altair GPCam3 290.

Currently I tend to do stacks of 7 to 10 seconds and up to about 20 in the stack, using my C11 at f6.3, or 15" Dob at f4.5 but could use my 7" Mak Cas.

Thanks for any help you can give in this technical mine field.

Mike

[Martin Meredith]

Hi Mike

Have you checked this thread: 

 

 

Looking at the table, I don't think you'll see such a big difference between the Ultrastar and the 174 (sure, there are some diffs, but perhaps not enough to be worth changing). The CCD will be easier in use due to not having to specify the gain, and the normal read noise advantages of the CMOS are no so apparent in the 174 it seems.

I think I'm correct in saying the 224 is colour (hence not in that table) while the 174 is mono. The 290 gives a much smaller FOV other things being equal (and IMO a not so useful aspect ratio). Having said that, it is a good EAA sensor in terms of read noise and QE.

Martin

[Mike JW]

Many thanks Martin. I have read through the thread - amazed at the work you did. I did not understand some of the technical stuff but got the gist of your research. A very helpful thread.  Cheers, Mike

[noah4x4]

There is one aspect of EEVA where high resolution, large sensor, small pixel truly excels.

I use Hyperstar @f/2. This means my images appear 25x faster, hence no requirement for wedge, polar alignment or guiding, etc. It also increases my FOV x 5, which is great as I can capture (say) the beauty of the Horsehead and Flame Nebula or many asterisms in one. The downside is for (apparently) small objects you then require greater camera Zoom.

My camera exceeds 4k UHD and my system is 'end to end' 4k UHD. Having so many tiny pixels available means that when applying Zoom, you can go much deeper before the image pixelates (goes blocky). Hence, small pixels, large sensor makes a Hyperstar (or NightOwl) system much more flexible. 

[London_David]

Forgive me if this is covered in Martins post - I only skimmed the linked post. 

The quick and dirty answer for performance is that with CCD you will always tend to be better with larger pixels (bigger receptors to collect photons) because you can’t bin CCD as effectively as CMOS due to noise. With CMOS sensors you can bin (add groups of pixels together to make a super sized pixel) with little to no penalty so pixel size is not something to worry about as much (it’s a little more complicated than that but...). Pixel size in CMOS cameras is usually important mainly in terms of your possible highest resolution (when looked at in combination with your telescope specs).

There’s more to it than this, but my rule of thumb is go for smaller pixels on a CMOS all things being equal and larger on a CCD all things being equal.

However, if I’m looking for a camera the important specs I’m looking at on CMOS are QE (as high as possible) and read noise (as low as possible) - and making sure the FOV matches my telescope for what I want to use it for.

I’d then check full well depth to give you a sense of how much dynamic range you can get in a single exposure (larger well allows for longer exposures before something overexposed). But this is less important for eeva than for imaging if you’re stacking anyway. 

Pixel size in a CMOS camera is not indicative of sensitivity performance in and of itself.

With the cameras you mention I have the 224 and the 290. The 290 is more sensitive by a large margin. Martin is right about the aspect ratio but actually for me that doesn’t matter since most things I’m looking at are very small in the frame. It’s just trickier to slew around by eye. The IMX290 sensor is old tech now (there are marginally better spec’ed new cameras ones I’ve not tried) but it’s still great bang for buck in the mono cameras. I think there are better colour cameras now (385??) than the 224 - though, again, more expensive. If you don’t mind mono and want a cheaper camera an IMX290 one is still what I’d recommend. I love my ZWO version and use it more than anything else. Keep in mind I’m into smallish galaxies so were I into nebula I may pick something different.

Edited March 10, 2020 by London_David

[Mike JW]

Thanks David, That is very helpful information/thoughts. I have a couple of friends visiting this week to find out more about EAA so combined with Martin's link this thread is very useful. Currently I am sticking with my Ultrastar but still fancy exploring a CMOS camera at some point. Mike