How to decide on lengths or number of ?

[autonm]

Im running a 200p HEQ5 with Canon 1100d camera.

I have managed to take images of clusters, planetary nebular and the M31 galaxy.

However i still consider myself to be very new to all of this.

My question is is there a general rule for the number and length of subs to take on a star cluster, single star etc as opposed to a nebular or galaxy.

I understand that a lot of this is experimental but instead of wasting precious clear nights - any advice on this?

Thankyou.

[ronin]

Have no direct knowledge but I would guess that a star, cluster or single, would be lower length of time. Guess that something like Pleiades could over expose a pixel or set of pixels on a sensor. So you end up with a "white" star immaterial of the stars actual colour. Then again most of the Pleiades are white to start with.

Would therefore expect shorter durations but likely more of them to bring out any negulosity present. Equally cannot think of any orange/red stars with nebulosity.

My thoughts anyway. :eek:

Have you found any significant differences?

[autonm]

ive been running everything around 20seconds - however some people have been telling me with an HEQ5 I should be able to get 1-2minutes without a 2nd camera tracking.

But just like you suggest I can see some targets being burn out.

Its cloudy out side at the minute ... per usual ... so I would though I would ask the experts 

[nmoushon]

You want to expose for as long a possible.

Different targets have different requirements.

Clusters and stars require short exposures. ~30sec or so.

Nebula and galaxies need as long as you can guide for.

But the trick is to combine the two and process it is PS (or such program) to pull out as much as you can with the long exposures then have a layer mask and bring it the short exposures to combat your over exposed stars and have nice colorful stars.

Thats the jist of it anyways. You can go into a lot of detail with S/N ratios in combination with your camera and scope. It gets very detailed lol.

[nmoushon]

For example on M45 you want to take long exposures (5min+) to get the nebulosity around the stars. Then you can come back and take shorter expsores(30-60sec) to get the correct star color. Then bring them together in PS.

With my HEQ5 and ED80 I was able to get 2min subs unguided. With really good polar alignment and good balance of the equipment on the scope and good weather (no wind) the max you'll get is 5min subs. But thats really hard to achieve and isnt perfect. You'll loose a lot of subs. Guiding is the best way to insure you loose as few subs as possible because of tracking errors.