On Jun 4, 2021, at 18:37, John Jennings <johnrogerjennings@...> wrote:



[Edited Message Follows]

Mike, Ted

If  you have not already, I would start reading Dr. Robin Glover's (SharpCap author) post in the SharpCap forums to get a basic idea about CCD vs CMOS. It's a little tedious but helpful.  SharpCap has a  built-in exposure calculator, but I have not used it since I still image with MaximDL for extended objects and galaxies.

https://forums.sharpcap.co.uk/viewtopic.php?f=35&t=456

Understand that sub lengths really depend on your Sky Background Noise. There's no way to be specific without knowing that. Sky Noise is dependent on your sky brightness, camera pixel size & QE, filters and f ratio of your optics. But it's the same issue in dark vs the city skies.

I first use Dr. Glovers online Sky Background Noise calculator.

http://tools.sharpcap.co.uk/

I then use a spread sheet I made up that uses the basic calculation for all kinds of sky conditions and telescope/camera combos. The spread sheet is based on:

Sub Length= K(Read Noise Camera*2)/Sky Noise

Where K = Is a constant based on  the percent of noise acceptable in a stack of images  vs a single sub of total integration time.  As a shortcut I use K of 5% and it's 9.76. What you learn quickly is how sensitive low read noise cameras are to Sky Noise.  I use 1.5e Read Noise for my QHY268C & QHY410C because that's where I set the mode/gain/offset at.  The QHY600C is nearly the same as the QHY268C. The 600C is just a full frame version. The Read Noise can go as low as 1.1e for the 410C and the absolute QE can be over 80%.  Compare that to 9-10e for CCD sensors. Plug a few numbers in.

Also helpful is this link:

https://snrcalc.vercel.app/

I try to moderate the calculations with common sense because they can show some ridiculously short exposures.  

If  I'm doing a star field with any OSC CMOS camera and a good sky pollution filter, I never go over 30 seconds in my sky conditions.  I've gone up to 4 minutes on subs with the same broadband filter targeting extended objects, (no gradients)  but have not been satisfied because of the low contrast. In fact, I rarely image extended objects in the city with broadband filters because of my Bortle 8 skies.  They simply wash out.

I have been testing broadband filters (IDAS P3 and equivalents) on Galaxies with some initial success at about 2 minute subs because they are typically bright. Not sure where this leads.

With the OSC narrowband filters like LExtremePro, Radian and IDAS NBX you can treat sub lengths like narrowband even in the city.  I've exposed  8-10 minutes with decent results and contrast like the IC443 image I posted.

Please take my experiences and comments with a grain of salt. This is a pretty complex subject probably beyond my pay grade and I'm learning and testing all the time.

On Jun 4, 2021, at 10:11, John Jennings <johnrogerjennings@...> wrote:



My perspective on color CMOS cameras is they have their own Genre like Spaghetti Westerns. (Good, Bad and Ugly fan) Trying to replicate narrow band images like a mono sensor with filters is problematic at best. As far a color saturation is concerned with broad band RGB images, I'm not sure about that. I do know that imaging with them took a rethink of my normal CCD imaging techniques. They gather data so fast, it's easy to start decreasing your signal to noise by exposing subs too long. In that case, long sub times may actually kill the image in brighter skies. And of course, there is the band passes of the Bayer Matrix filters to consider vs individual traditional RGB filters for mono camera.

You need to break up your integration time into a larger number of subs of shorter duration if you are broadband imaging. With narrow band OSC filters like the LeXtreme Pro (7nm band pass on Ha, OIII)  it doesn't matter very much.  Of course you need long integration times, but at the proper sub time. This of course is problematic with smaller pixel Cameras because the files are so large. But computers and SSD drivers are cheap, and new sensors like the IMX410 with 5.94U pixels give me hope that larger pixel CMOS sensors may eventually appear because they are optimum for commercial low light camera applications too. 

Just remember that short CMOS subs have the same information that a longer CCD subs have normally if all other variables are the same. I've been using a portable SQM meter with separate Red, Green, and Blue filters over the lens (simulating what the OSC sees) while stacking various OSC filters over them to take sky SQM readings. I then use that to determine optimal sub exposure time limits for my CMOS OSC. Of course there is a lot of wiggle room there too.  It's almost impossible for me to image with CMOS color cameras in Bortle 8 without some kind of light pollution filter. Sky fog can be an issue after 5 seconds easily causing washed out images. It's really amazing how much light pollution filters reduce the SQM readings of the bright city sky with great transmission. With my sky MPSAS of 17.87 (Bortle 8.1),  the sensor under the red filter of the OSC matrix and an IDAS D2 filter sees 20.52 MPSAS or Bortle 4.10.   Of course they filter out good colors too.

Go with George's recommendation.

The TSX ascom driver can be found on the bisque site, if you choose TSX. Use this link to download it  https://www.bisque.com/wp-content/x2standard/

Just FYI, I used TSX with my 1100 (no encoders) for years. When I added my Mach2 (with AE of course) and set up for remote imaging I quickly learned that TSX was (1) unnecessary and (2) created a potential source of problems. My routine now is to use APCC to initialize the mount, start up SGPro to slew the telescope to the desired location (preset), then do a platesolve for final positioning and camera rotation, and then start the imaging sequence.  No need for a planetarium program.