Page 1 of 1
Altair 26c smart histogram
Posted: Thu Nov 26, 2020 7:31 am
by AndyM274
Hi all,
After performing sensor analysis on my Altair 26C in ultra mode, last night I wanted to find what my optimum exposure time would be so I ran the smart histogram.
It came up with some data that I'd like your opinion on as I'm certain it's not correct - it's telling me that with my L pro max filter in i only need 34seconds.
Screenshot attached.
I'm using the latest 64bit version of SC.
Cheers
Andy
![20201125_203124_copy_858x650.jpg](./download/file.php?id=3836&sid=7569a3b8961def0e4879e013f1930003)
- 20201125_203124_copy_858x650.jpg (169.54 KiB) Viewed 2079 times
Re: Altair 26c smart histogram
Posted: Thu Nov 26, 2020 7:47 pm
by admin
Hi,
The rule of thumb value (for 10% allowed extra noise) is 10 * read noise squared / sky brightness. My analysis of the 26C in Ultra mode gave the read noise of 3.2 at minimum gain, so putting the values in along with your sky brightness of 2.74 gives an estimated exposure of ~38s, which isn't really that different from the value that you are getting. The only thing that might be causing issues is if you're sky brightness measurement was incorrect for some reason. You can use the calculator here at
http://tools.sharpcap.co.uk to do an independent estimate based on your bortle number.
If you compare that with the 294 sensor, that sensor has a read noise of about 7e at minimum gain, so would require exposures that were four times longer.
As always, remember that there is no reason that you shouldn't use longer exposures than the recommended ones if your mounts tracking/guiding is up to it. It's just that going to longer exposures won't improve your final image quality once you've gone past the recommended level (or at least the most extra quality you will get is a 10% reduction in noise, even if you go for a single 3 hour sub...)
Cheers, Robin
Re: Altair 26c smart histogram
Posted: Sat Nov 28, 2020 8:58 am
by AndyM274
Perfect thanks Robin - just wanted to check as it seems too good to be true.
Cheers
Andy