Number and length of subs

[nCognito]

Does 20 x 30s subs approximately equal 10 x 60s subs?

[Gonzo]

Topic has been discussed many times, have a look for example at the following post:

[SnakeyJ]

The short answer on this is no, longer subs will resolve fainter details not present on shorter subs, there was an excellent thread/debate running on this here recently - with some great insight from Steppenwolf and Ollypenrice, but I can't for the life of me find it!

Craig Stark provides some excellent articles on CCD Signal to Noise Ratio Parts 1 - 6, which goes in to a lot of the theory but is very well written and easy to follow

[SnakeyJ]

Topic has been discussed many times, have a look for example at the following post: http://stargazerslou...-summer-nights/

Well done Gonzo that was exactly what I was trying to find!

[Gonzo]

no problemo, it's a topic I've put in my 'Content I Follow', it's a very good post to read with lots of excellent info.

[ollypenrice]

It's important to note the difference in circumstances between a cooled and an uncooled camera and between a dark site an one afflicted with LP.

An uncooled camera and a light polluted site put an upper useful limit on exposure time. A cooled camera from a dark site will go deeper with fewer but longer subs.

The answer to your specific example, though, is 'yes.' They will be roughly equivalent. But take a cooled camera to a dark site and then compare 10x30 minutes with 300 x 1 minute and you'll see an enormous advantage to the former on a faint target.

Olly

[Jessun]

Simple answer:

Take the longest subs you can accieve all things considered, including for example mount performance, alignment, camera type and seeing/vis. (This is often trial and error at first).

Then take as many as you can.

Unless you are on a holiday at some unusual latitude with a very specific time frame, all targets come and go year after year, so patience will eventually pay off. If indeed you only have a set time available then personally I'd try to make sure I have around 20 subs to make the most of the initial S/N boost as the noise gets averaged.

/Jesper

[nCognito]

It's important to note the difference in circumstances between a cooled and an uncooled camera and between a dark site an one afflicted with LP.

An uncooled camera and a light polluted site put an upper useful limit on exposure time. A cooled camera from a dark site will go deeper with fewer but longer subs.

The answer to your specific example, though, is 'yes.' They will be roughly equivalent. But take a cooled camera to a dark site and then compare 10x30 minutes with 300 x 1 minute and you'll see an enormous advantage to the former on a faint target.

Olly

Actually, without being too much of a kiss Bottom, I was talking to someone who had stayed at casa Penrice and I was thinking of doing the same, so perhaps I can get a practical demonstration then.

My question specifically relates to DSLR imaging at a suburban heavily light polluted site, that is where I live and my wife has no plans to allow me to move. I am typically imaging over security lights and unless I am pointing near the zenith I collect huge amounts of noise even in 1 min images which I find impossible to properly process out without losing detail. (When pointing towards the zenith however, I can go to 3+ minutes, 30 degrees of pointing angle makes all the difference).

So for RGB, I'm probably going to go down to 30s, alternatively, I could stop down 2 stops, which would also help with the vignetting. My current project is to use 50 - 200mm lenses on the Astrotrac and see what I can get.

Anyway, thank you for the Yes/No answer, it beats reading through huge threads that I just don't understand and don't really seem to have that much bearing on what I am trying to do..

[ollypenrice]

Actually, without being too much of a kiss Bottom, I was talking to someone who had stayed at casa Penrice and I was thinking of doing the same, so perhaps I can get a practical demonstration then.

My question specifically relates to DSLR imaging at a suburban heavily light polluted site, that is where I live and my wife has no plans to allow me to move. I am typically imaging over security lights and unless I am pointing near the zenith I collect huge amounts of noise even in 1 min images which I find impossible to properly process out without losing detail. (When pointing towards the zenith however, I can go to 3+ minutes, 30 degrees of pointing angle makes all the difference).

So for RGB, I'm probably going to go down to 30s, alternatively, I could stop down 2 stops, which would also help with the vignetting. My current project is to use 50 - 200mm lenses on the Astrotrac and see what I can get.

Anyway, thank you for the Yes/No answer, it beats reading through huge threads that I just don't understand and don't really seem to have that much bearing on what I am trying to do..

OK, it's important to know your specific circumstances because a general answer for ideal conditions would just say 'long exposures.' This is not going to be the right answer for you and I'm the last person to give you advice on how to beat the LP because I don't have any! Jesper, who also responded, is now getting remarkable results from a seriously difficult venue which I happened to visit last week because my son in law lives a few hundred metres away! Help is out there for LP imaging but I'm not going to pretend to know much about it.

One thing, though; in my experience Pixinsight has gradient removal and colour calibraton tools which are not so much second to none as a thousand miles ahead of the rest. It would be my first port of call in your situation.

Dare I say monochrome CCD and narrowband imaging?

Olly

[nCognito]

OK, it's important to know your specific circumstances because a general answer for ideal conditions would just say 'long exposures.' This is not going to be the right answer for you and I'm the last person to give you advice on how to beat the LP because I don't have any! Jesper, who also responded, is now getting remarkable results from a seriously difficult venue which I happened to visit last week because my son in law lives a few hundred metres away! Help is out there for LP imaging but I'm not going to pretend to know much about it.

One thing, though; in my experience Pixinsight has gradient removal and colour calibraton tools which are not so much second to none as a thousand miles ahead of the rest. It would be my first port of call in your situation.

Dare I say monochrome CCD and narrowband imaging?

Olly

Thanks for the steer, I have just had a look as Jesper's work and he is getting great results that I am extremely envious of.

Perhaps I will load the image into the processing section and try and get some tips there. I have been following Harry's excellent tutorials but still without success.

[Earl]

As Olly says, the answer to this is more about the local environment than the theory of CCD Imaging.

I feel it breaks down to.

Local Enviroment

Equipment performance

Target

Theory implementation