How deep can you go?

Discussion of using SharpCap for Deep Sky Imaging
Cybermystic
Posts: 34
Joined: Wed Nov 03, 2021 8:33 am

Re: How deep can you go?

#21

Post by Cybermystic »

Hi Brian,

That is very good advice. Where I'm coming from on my question is that there's a guy on the Hyperstar forum who took a very nice image of the Squid nebula using a whole bunch of 10-minute subs. The calculator would give a sub length of less than a minute. He took a bunch of 5-minute subs and saw nothing. If you don't have the integration time on very dim objects then you ain't gonna get enough signal photons to work with, in my dim view of the world :D

Greg
User avatar
oopfan
Posts: 1321
Joined: Sat Jul 08, 2017 2:37 pm
Location: New York
Contact:

Re: How deep can you go?

#22

Post by oopfan »

Greg,

Remember, signal and noise are are married at the hip. So, what you perceive is the ratio of the two. If you can't see the DSO, then you've got a low SNR. It doesn't necessarily mean that you've got no signal, it can also mean that you've got too much noise in relation to the signal.

When you say "you can't see the nebula with 5-minute subs but you can with 10-minutes subs," are you saying that you are comparing ONE 5-minute sub to ONE 10-minute sub? Or are you comparing TWELVE 5-minute subs to SIX 10-minute subs, therefore ensuring that the total integration time is the same? Is he using a narrowband filter? With a large aperture, Hyperstar kit you shouldn't need long exposures unless you are doing narrowband.

Brian
Cybermystic
Posts: 34
Joined: Wed Nov 03, 2021 8:33 am

Re: How deep can you go?

#23

Post by Cybermystic »

Hi Brian,

Yep - you've clearly got this all worked out perfectly. I'm not sure of the details of the guy with the Squid, but I am pretty sure that what you are saying is spot on. I got sent a pretty reasonable image of the Dolphin Head nebula taken on a Hyperstar with 100 x 60-second subs - so seeing that I reckon all you've said pretty much all hangs together. I still find the result counter-intuitive - but there it is. The other thing that has been made clear is that the older CCD cameras need a lot more sub-exposure time than the modern CMOS cameras. I had no idea that the CMOS cameras had improved so much over the years, whereas the CCDs, with no real R&D over the years (because CMOS is the way sensors are going) have stood still for over 10 years.
Great stuff!!

Greg
Post Reply