Any deep sky imaging tips for unguided 12.5" & 400D?

[John K]

Well guys I am planning on getting out to a really dark sky site this coming weekend for my first real try at deep sky imaging. I will be equiped with a 12.5" and Canon 400D.

Limiting factors are the fact that I will only drift align my mount and will not have any guiding corrections for the prime focus shots and will only have 2 x batteries for the 400D. As such at this stage my plan was to limit my exposures to 2-3 minutes (is this realistic without guiding) at either ISO800 or ISO1600. Planning on having the noise reduction turned on. As I am looking to experiment, on my prime focus target list I have NGC104, M1 (ISO1600), M42, Horeshead (ISO1600), Tarantula, Jewel Box, Eta Carina, Omega Centauri, M104 (ISO1600), M8 (will be low) and Comet McNaught.

Am I wasting my time with these objects with my set up? If taking 2-3 minute exposures, what is a good number to take (remembering I only have 2 400D batteries) or am I just dreaming here with my huge tick list?

Advice and thoughts appreciated!

John.

p.s. and yep, Staturn and Jove are on the tick-list (I know it's the deep sky forumn) but laptop and 17amp powertank will be tested.

[Gama]

For starters, you should have a swag of batteries. When i bought my 20D, i bought 8 spare bataries at $11 bucks each, on ebay (New).
Keep your exposures short to stay under any errors that may show, so trial and error will dictate how long your exposures will be.
Apart from that, you should be OK.

[jase (Jason)]

With the 12.5" F/5 having a focal length of around 1580mm, you are going to experience star trailing much sooner than you think. 2 to 3 minute exposures are too long for unguided exposures at this focal length.

Refer to these formulas.
http://www.astropix.com/GADC/SAMPLE7/SAMPLE7.HTM

In the example provided a 50mm lens will experience trailing in 8.5 seconds along the celestial equator.

If anything, hit the bright objects, but certain keep exposure times very low.

[Garyh]

Hi John,
You have some serious focal length there and assuming you have a eq6 mount with goto, make sure you drift align well and if you have time before imaging each target do a PEC run..I don`t know how long you will get and the number of bloopers to good pics will be but the shorter the better, with my setup (850mm focal length) with 1min exposures I might get 80% good then with 2min maybe 40%. Any more than that its just good luck...So I would stick to the brighter targets like m42,eta carina, m8 or mcnaught. Don`t try to do too many things in a night and just work on the brighter ones..and keep to 1 min or less. By all means try some longer ones you never know..
If you know how to use and take and process dark frames I would recommend turning off noise reduction since you only have 2 batteries, you will be using half your reserves just by letting the camera remove noise even with the bloopers. You should get close to 2 1/2 - 3 hours before you run out off juice, depending on the temp etc...
Good luck and hope you nail a few good ones......
Cheers Gary

[avandonk]

The other trick you can use is median average every second image, ie median average odd and even and then SUM. This is the equivalent of doubling your exposure. And of course every third or fourth if you have enough frames.
This also evens out any sensor noise as there is bound to be some drift being unguided.

Bert