David, great work. I presume the 150mm is a camera lens? What kind of ISO setting and f/ are you using? How are you mounting the kit and tracking it. And how are you judging focus? And one final question, sorry, how are you stacking the data? It would be nice to see a photo of your set up. 

James

James,

The lens is a Sigma macro 150mm f2.8. I am using it wide open. The ISO is set at 6400, The sensor on the Nikon D7200 is particularly good in low light. I mount the camera on a fixed tripod, no tracking. I focus by using live view and set the focus to see the maximum faint stars. The exposure is set at 2.5 sec to minimize star trails. I set up the intervalometer to take six lots of nine frames. I stack the images in Deep Sky Stacker.  I hope that covers it.

David

That's useful, thank you. I'm really impressed with the results you are getting with the set up you have. Have you used any software on the laptop and connected the camera to it with a USB lead? I've found that makes focusing easier and more accurate; I wonder if getting the focus even more accurate would tighten up your stars further, or if that is just due to being on a static tripod even though the exposures are very short. Is there much vibration from the mirror or do the Nikon's have a mirror lock up mode?

James,

Thanks. I have looked at the "mirror up" setting but it seems limited to single shot mode. I think using live mode on the camera should be OK, as I can zoom in to look at the stars in close-up. I will try focusing with my tablet though.

Cheers David