9 replies to this topic

[robodan]

Found this interesting.

https://youtu.be/bHS34OszAwQ

He claims for video astronomy you want a small chip and large pixels, why, more senstive and collects light much faster, smaller pixels not as senstive, same as large chips, spread light.

For astrophotography it does not matter as your doing very long exposures.

His talk is interesting and goes against what many here are using?
So does this mean, and according to what he says, the Orion Starshoot g4c would make the better WAA camera.I know my Revolution imager is extremely quick at capturing images and certainly much faster than the ASI224 which is commonality used.

But of course lower resolution and this is what he cliams, bigger pixels more senstive chip, but suffer resolution.

Guess you cannot have it both ways.

He gives exact reasons why you should be using big pixel cameras, rather than smaller pixels

[bips3453]

From what I have learnt, sensor's pixel size has to be in acceptable range for the focal length. https://astronomy.to...cd_suitability 

Edited by bips3453, 25 February 2021 - 07:09 PM.

[CoHPhasor]

^ Beyond the above, a smaller chip means a faster read time.
(That's why you get so many more frames from using small ROI)

 

 Focal length paired with pixel size does matter, but generally it is easier to fill bigger pixels than smaller.
(Though there is a diminished return when you use a mono cam that is backlit, as the filters/wires are not blocking the path to the tiny wells.)

[SanjeevJoshi]

FoV, focal length, pixel size / ratio, focal ratio etc  are all connected.

 

Talking about bigger pixels being better is like talking bigger FoV is better, with no context.  Bigger FoV is better because you can see more.

[nic35]

Kind of old school.  And, in my opinion, wrong.

 

He says you need a guide scope to do CMOS EAA with - really ? 

 

And you need a GEM - Really ? 

 

Neither true in my experience.

 

And what about binning the CMOS to make the pixels larger ?  

Edited by nic35, 25 February 2021 - 10:10 PM.

[robodan]

Yes, you can make bigger pixels also it maybe a must on some nights to match your seeing conditions, He does say simple EAA is possible with a simple system, If your saving frames to PC an EQ mount maybe needed else you have to process field Rotation is out. I pefer live stacking, not saving to PC. Sharpcap takes care of rotation as its basically live, when getting a great image hit save and save as a png image and not saving all those other stacked frames. 

 

Live stacking is very possible on an Alt Alz mount.

 

Looking at an QHY183C use at the Moment a 120MC-S and know the  spacing for a 0.5X is 59mm, and got this from the asi224 spacing which is 5mm less

[Astrojedi]

This is not correct. I have spent years trying to correct these misconceptions on these forums. Most of these rules of thumbs were created for CCDs and subpar optics. 

 

Even with my typical seeing of 2” - 3” I see a difference in detail resolved when imaging /EAA at 0.5” / pixel vs. 1” / pixel.

 

In sensor design the real determinant of pixel size is read noise. A lower read noise sensor (assuming similar QE) will produce a higher SNR and better dynamic range for the same pixel size.

 

Further, in CMOS with read noise approaching 1e or lower pixel size is nearly irrelevant. Binning incurs very little read noise penalty so you can really create a sensor of any pixel size on demand.

 

My ideal sensor would be one which has 90%+ QE, read noise <0.5e, 14 stops of DR and pixel size of 1 micron. Then I can create any pixel size I want on the fly via SW binning. In practice 2 micron pixel size is more likely.

[Ptarmigan]

Kind of old school.  And, in my opinion, wrong.

 

He says you need a guide scope to do CMOS EAA with - really ? 

 

And you need a GEM - Really ? 

 

Neither true in my experience.

 

And what about binning the CMOS to make the pixels larger ?  

I have taken exposures of 30 to 45 seconds with EAA and never thought of a guidescope or autoguiding.

 

I have great results. 

[Noah4x4]

I use two cameras with 4/3" sensors, high resolution, small pixels in an end to end 4K UHD display system. The results are great, particularly when I use Hyperstar where FOV is huge, but that means lower magnification. Zoom is then desirable and inevitable the smaller the pixel the greater the Zoom possible before pixelation (going blocky).

Totally agree with AstroJedi (and Nic35). I use Sharpcap Pro Smart Histogram and Brain to guide me to the best combinations of exposures and Gain and Auto-stretch and Auto-colour-balance magically puts me in the right ball-park. You can largely ignore the old rules for CCD given low read noise CMOS.

Edited by Noah4x4, 27 February 2021 - 01:58 AM.

[MrRoberts]

I commonly do 30s unguided eaa with both my 80mm and C-6 on CEM25 mounts using a 294mc.