IainUK wrote in post #10763579
Just before I waste a load of time can I just confirm that after I have taken a load of 20-30 sec exposures at night every one is just going to look black and that after I stack them something will 'appear'?! (hopefully) - Due to using a MAC I cant use Startrails and any other software that is shareware only lets you stack 10 photos unless you buy it. So before I buy some SW I just want to make sure that I have the raw ingredients!
If anyone can recommend ome good stacking SW for a MAC I'd be grateful.
Thanks
Yes, and no 
If you stack 300 truly black frames then the end result will be.... a truly black frame. If, however, you take 300 frames which contain a single star, the brightness of that star will vary over the frames, due to differences in noise, the atmosphere ("seeing") etc. What the stacking does is average all this out to give a true pciture of what was there. Multiply this by lots of stars and all of a sudden, you start to get a good image. Similarly, if there is information in the darker areas of an image, it may not be immediately obvious because of noise etc. By stacking multiple images (and using dark frames etc) you can reduce the noise and increase the signal, thus giving a better image. In essence the stacking gives a better signal to noise ratio in the final image. It does not, however, increase the brightness of the image. If there isn't any information in the frames then stacking them won't help.
See here as one page with a more detailed explanation, or the simpler one here from wikipedia.
Hope this helps.
PS, why not dual boot, or even run a PC in a virtual machine on your MAC? Then you can take advantage of all the PC software available
