Starting point for CCD exposure?

[buzz]

There are obviously many variables in play but does anyone know of any resources which can indicate good starting points for exposure for a given aperture, pixel size, ADU and sky quality?

All the books I have on the subject skip over the subject of determining exposure, which is a bit worrying! Even the nebulosity instructions are a bit skinny on the subject.

[ollypenrice]

I don't know of any such resource and tend to suck it and see. I'd give it a whizz at 10 minutes for L and 5 minutes for R, G ad B. For Ha go for as long as your guider will stand. That should get you started on finding what works for you and your sky, assumng you are not pointing at M42 with its notorious dynamic range.

Olly

[swag72]

In the 'New CCD Astronomy' book by Wodaski, he has a table that gives an idea of a starting point.

For Globular and Open Clusters - 1 min

For Galaxies - 5-10 min (Very dependant though on the type of Galaxy it is)

For Nebula - 5-10 min (As above)

As he says, if you take a 10 min exposure of M42 for example, you will have a very blown out core, the same for M31, so it really is down to experimentation. These are just starting points though in my mind.

Perhaps such a resources doesn't exist due to the number of changing variables. Olly has given good advice - And certainly when I tried a globular cluster the 1 min was a good starting point as well.

[ollypenrice]

For M42 you need to follow this routine;

Compositing 2 Different Exposures via Layer Masks

In my copy of the Wodaski CCD book there is a technique for doing this which really is terrible! Follow Lodigruss on this one.

Olly

[buzz]

Logigruss - that name rings a bell - he's the chap with the online book for sale right?

I'm so used to the science and variables of monochrome photography it is really wierd for me to just suck and see with digital on a scope!

[JimStan]

One big difference, is you are NOT wasting FILM !

[buzz]

True - though I think time is more valuable these days! I designed several darkroom meters in the past, which use the same sensors as a well known sky quality meter.....I was just musing, whilst the rains comes down....

[JimStan]

Ahhhh - - "when the rain comes down" - - That's when you PROCESS the data you have collected ! :)