How do you know the best exposure length to use?

[ashworthacca]

Hi guys, the other night I got a great nights imaging done but I'm struggling with the processing.....finding the images noisey.....and started wondering if the exposure time is too high/low, inparticular when considering light pollution.

Here's a 5 minute and 10 minute sub, not processed at all just converted to JPEG, and wonder what you guys think. Are they too washed out/over exposed? I use a CCD Eos Clip filter.

2011-03-07_20-13-57_Heart0002_ISO800_600s by ashworthacca, on Flickr

2011-03-07_20-02-35_Heart0001_ISO800_300s by ashworthacca, on Flickr

Would be interested in hearing your thoughts on how to ascertain the best exposure length.

Thanks:)

[Sparrow]

I find the main problem that the EOS clip filter can't eliminate is the sky glow caused by LP that it doesn't filter and a certain amount of natural sky glow - the longer the sub, the more apparent this becomes to the point that it begins to wash out the detail. For that reason (and I know there will be differing views on this) I tend to prefer shorter subs and lots of them - the 5 minute sub looks good whereas the 10 minute one is beginning to look a bit washed out. Depending on conditions on the night, perhaps you could try some 6 or 7 minute subs. It does look though as if the 5 minute subs has plenty of detail once processed.

[Psychobilly]

I used to use shorter exposures at higher ISO to work out what I could get away with on any particular night and target...

Billy...

[ashworthacca]

Thanks guys.

The 10 minute one does looked to be washed out........but there does seem to be detail there. Is it just trail and error or is there some way of knowing that at a particular exposure level the detail is being lost?

[themos]

You need to look at the RAW files with Canon's DPP and turn on the "Show highlights" feature. That will tell you how much you've overexposed, there will be a lot of blood-red areas. If you haven't overexposed (except the odd really bright star) and the tracking is good, stay with the longer exposure.

[ashworthacca]

You need to look at the RAW files with Canon's DPP and turn on the "Show highlights" feature. That will tell you how much you've overexposed, there will be a lot of blood-red areas. If you haven't overexposed (except the odd really bright star) and the tracking is good, stay with the longer exposure.

ahhh, great.....that's what I wanted to hear.

Thanks themos:D

[heroes_46]

Great stuff I was looking for the same