Timeing to stop star trails

[Taff]

Hi' Can any one help me out.How long should a capture be so i won't have star trails.At prime focus which is the best iso setting for DSO Thanks.Mark

[jgs001]

That's a tough one Mark. Can you provide more information on what focal length, what mount, where in the sky your pointing etc please ? The ISO question is more related to the capabilities of the camera I think. ISO800 seems to be the readily accepted setting for Canon's. But .... I've used 1600 when using an AltAz mount.

[Reggie]

Hi Mark, it all depends on your mount type (alt/az or eq) and it's tracking really and how well aligned it is, an unguided mount will have a tendency to move about across your target causing trailing/elongated stars over a certain exposure length.

I would start at 10sec exposures 10 at a time, and examine them to see how many 'good' images you get out of the 10, set the camera to iso 1600 while you do it as these are relatively short exposures it will give you more detail to check things by, I would then try pushing the exposure length up to 30seconds, take 10 again and check how many good images you get, its really up to you to decide how many wasted shots you are prepared to lose to get a target and of course you can always increase the exposure length above 30s if the tracking will allow it.

When I started out I was losing a heck of a lot of images, 70-90%, once I'd worked out the best exposure lengths I was happy losing 40-50% of images, taking into account my limitations as an imager and the unsuitablilty of the kit I was using this was a fair level of loss as I was more interested in getting image data to play with than spending money on kit to make the situation better.

[Taff]

Thanks Gents for the information.Mark

[rawhead]

Asked a similar question myself some time ago...

I find this useful.