the ideal exposure time depends on many factors that are not known by INDI/Ekos. Mainly SQM and some feature of the camera like QE, dark current, read noise, FW depth have impact on the optimal length of the exposure.
I would rather use simulators that available online or as excel file.
I even tried to write one for myself but my personal experience is that, despite the theoretical model being perfect, the uncertainty on some inputs is affecting the results so much that an empirical approach based on trial and error is more valuable.
I have similar equipment: William Optics 71 f/5.9 and Altair 290M.
With my Bortle 5 skies I regularly use 60s exposure in Luminance.
If you have Bortle 4 skies then I would recommend 120s exposure or more.
Keep your gain low. Use an Offset of 30. Does ZWO give you access to Offset anymore?
There is no harm in taking longer exposures except that more stars enter saturation.
The benefit is that you increase the SNR of everything including faint nebulosity just above the level of sky glow.
It is a trade-off.
The problem with the 290 is that it doesn't have a very deep well, only about 7000 electrons. That means it is difficult to get accurate star colors over a wide range of magnitudes. Also, the 290 is not cooled as you mentioned. This is especially problematic with summertime temperatures. I highly recommend that you capture darks BEFORE lights.
I recently purchased an Atik 314E. It is 10-year old technology but I get far superior results. Cooling but not set-point.
There's a product by Skyhound called Sky Tools which seems to fit my requirements. It's not cheap at USD200. I'll probably buy it eventually but it would be good if it integrated with KStars/Ekos. It already integrates with APT and iTelescope.
Hey Jasem, would it be possible to look at how easy/hard it would be to integrate this?
SkyTools works very well and I have been using it for my visual observing for several years now. The drawback is that it only runs on Windows. It is possible to make it work on Linux and Mac with wine but it has its limitations then.
Wouter van Reeven
ASI6200MM and 7 slot 2" filter wheel with a SkyWatcher Esprit 80 ED on a SkyWatcher HEQ5-Pro
ASI1600MM-Pro Cooled and 5 slot 1.25" filter wheel with an 8" TS Ritchey-Chrétien on a SkyWatcher EQ6-R
One can calculate SQM for the patch of sky the telescope is looking at pretty simply, given an exposure, a dark and a bias (OK maybe a flat too if you want to be very exact), and the bandwidth of the filters used.
I believe, that when people quote SQM values, they're talking about a much wider-field exposure--e.g. something like 60-degrees wide, thus less affected by any nebulosity you might be pointing at. Probably also encompassing most of the visual band--e.g. if you use filters, and calculate your own SQM, you may find your "blue SQM" is somewhat different from your "red SQM".
SQM is an interesting number, but really I believe what thread is about is getting a good exposure values. My (gut feeling) belief on this is that if you're in the ballpark (e.g. if 240s was "optimal", 120s is probably in the ballpark, but not 10s), not saturating parts of the image you care about, stacking your subs for your final image, and have a modern camera with reasonably low read noise, then getting precise with exposure is overkill. Disclaimer--I've never won any image-of-the-day or top-pick awards
A commonly used technique is to expose the subframe to be shot noise dominant vs read noise dominant. This is done by exposing a frame till the sky background is some factor of read noise squared - usually a factor between 3 to10 or so. To do the calculation you need to know read noise, gain and offset of the camera.
By exposing to be shot noise dominant, the SNR improvement by stacking approaches that of a single long exposure with the same integration time but with reduced saturation issues.
RPi3 Ubuntu Server 20.04, Windows 10 AMD64, AAEON UP Core Ubuntu Desktop 20.04
Avalon M-Uno, EQ6 Pro, Atik420, ASI1600MM-C, ASI120MM-S, DBK21AU04, ZWO EFW, Optec TCFSi
Vixen R150S, GSO RC8, ST80
This is an idea that crossed my mind. But I don't know how to do that. In fact, that will be an excellent option in the capture tab.
The SNR is computed with guiding camera, could it be possible to do it with the principal one, ans would it be a sufficient information to compute a capture time ?
Sharpcap has a camera calibration, i can exports the results of this calibration. Additionally Sharcap have an smart histrogram to peerform a exposure suggestion. NINA can import the calibration file from sharcap, and can perform an exposure calculator with this calibration file. I don't know how to do it, but can be a great improvement for EKOS.