[JohnH]

I was testing out GuideMaster again last night and with some pleasing results too I must say. I am limited still by the short exposure support for the LPI to tracking on stars of Mag 6 or brighter approx however I found this pretty object while hunting for trackable targets. Exposures are 2 minutes guided at ISO400. Processed in IP and PS.

A couple of qusetions have occured to me as I get deeper into this:

1. What is the best ISO setting to use for DSOs - ISO 1600 would appear to be best - but I see folks using 800, 400 even talk of 200. What advantage do the lower ISOs bring?

2. I appear to have more pronounced vignetting on the longer, lower ISO shots, is that normal - so I need to take flats now something I have not done yet. To do this I should shoot a clear dawn sky at ISO100 and a fast exposure and greyscale the result, yes?

3. Darks and flats must be taken (RAW or JPEG) to match the lights ?