Question about narrowband sub lengths

[Ags]

What are typical sub lengths for common narrowband filters, assuming an F5 light-gatherer? Obviously it depends on the target and on the guiding capacity.

Is there a difference between sub lengths for CCD and DSLR? I presume DSLR can't go much over five or six minutes anyway...

[johnrt]

Aim for as long as you can possibly go before you get guiding errors. Unless the target is very bright, M42 for example, anything over 10 minutes will yield decent results.

[Ags]

But won't a DSLR start getting too noisy after 5 or 6 minutes?

[steppenwolf]

There is so much variability depending on object but a really rough guide for me would be 5 minutes for a DSLR, 5 to 10 minutes for an cooled astro CCD either (one shot colour or mono plus RGB filters) and as much as your tracking can handle for luminance and narrowband filters.

That is such a generalisation though!

[johnrt]

I used to do 10 mins with a canon 1000d, only on warm summer nights (about 20C) did it get too noisy.

Trick is get as many subs as possible & shoot some darks!

[Ags]

John, that was 10 mins at what F ratio?

[johnrt]

John, that was 10 mins at what F ratio?

It was at f/5 on a 6" reflector and f/2.8 with a 135mm lens - the response to Ha wavelength isn't massive on even a modded DSLR.

Don't worry about it too much, just aim for the max time you can before you get tracking errors & bag plenty of subs.