What subs would I need with a different camera?

[swag72]

I'm just bumbling along the highway that is astrophotography. Unfortunately I realised too late that it is a very long, expensive and difficult road to navigate, with lots of blind corners and cul-de-sacs along the way!

So in my quest for enlightenment and overall knowledge I have the following question.

At the moment my modded DSLR with Ha clip in filter takes 20 min subs. I get useable data with that, using my 120ED with a 0.85 reducer / flattener - So if I'm right that takes me down to f/6.8?

If I were to use a CCD instead - Say an Atik 314L for example - How much shorter would the subs be for roughly the same amount of data capture? I know that as mono and no debayer matrix other things come into the mix, but just rough ideas would be good.

If I were to change my scope, but stick to the modded DSLR, how much shorter would subs be? (Obviously that depends on the scope and speed of it, but humour me and give me some ideas!!)

Can people point me towards for example a modded DSLR sub and a CCD sub taken with the same setup and for an equal length of time so that I can see the sort of difference?

[martin_h]

Sub time could be less with a more sensitive CCD - BUT! it will also pickup any LP just as quick....Your example of 20mins Ha, for the same data you would probably do it in 15 mins, but I use a f6.something scope and go for 20 mins in Ha anyway for the depth.

Same answer for a faster scope realy.....Yes the sub time will be less for either, but that doesnt meen you have to, or would want to go shorter...if you want depth to an image its needs time on chip.

[swag72]

Thanks for that Martin - So realistically, if I'm managing 20mins with the DSLR, I'd probably be looking at similar subs, but it would pick up more detail - Makes perfect sense. Cheers.

[martin_h]

With all things being equal...but as you know in this game nothing is....

[Uranium235]

Firstly, compare the QE of the Atik and a moddded DSLR. You will find the 285 chip QE is far higher than any DSLR, especially in Ha. So you can get the same signal (as the dslr) for less time, but as martin said you could just continue to let it run for the full 20min for extra depth. But at 20 min its a bit difficult to get a large amount for a good stack. Depends on what target youre going for really, its dynamic range is also another factor.

My ED80 runs at f6.38, and I found that 10min subs are usually enough for most things, with the occasional 15min sub thrown in when chasing wispy bits (and when I know my polar alignment is good!).

Factor in the difference of noise between a DSLR and a 314, and its a no-brainer.

[ollypenrice]

The best DSLR images that I've seen, and some do rival CCD apart from on star colour, are taken in very fast optics. The problem of heat build up seems to lift the noise on long subs with DSLRs so you gain progressively less in terms of SN ratio. A cooled CCD can expose for as long as you like.

If keeping your DSLR I would say go for a fast astrograph. Tak Epsilon would be very nice thank you!

If keeping your 120 I'd go for a sensitive CCD.

If going bananas I'd go for a sensitive CCD in a Tak Epsilon!!!

Olly

[swag72]

Oh Olly, that yellow scope looks lovely!!! Nice price tag too!!

I think I will be keeping my 120, so I hope initially to go for an Atik 314L. My, my, this is certainly an expensive hobby!!

[ollypenrice]

Oh Olly, that yellow scope looks lovely!!! Nice price tag too!!

I think I will be keeping my 120, so I hope initially to go for an Atik 314L. My, my, this is certainly an expensive hobby!!

Buy me, buy me, I'm yellow and lovely...

[swag72]

I nearly bought a car for the very reason that it was yellow!!!!!