Focus is everything when it comes to astrophotography. I was just reading at Sciastro the other day and they guy was saying your focus looks to be a micron off. A micron off? If I could get that close I would be elated. As the stars are at different light years away you have to change your focus each time with a telescope, especially if you are trying to make out a double star.

I don’t know of a telescope that has an infinity focus point like most binoculars and most camera lens. I spend 5- 10 minutes trying to get the best focus when taking pictures and then they aren’t always spot on. The difficulty is seeing the object through the camera lens, which is a tiny view, so I imagine with that ISS shot the image was viewed on a computer screen and focused by someone while another person snapped the shot at the correct focus.

There are a couple of focus software out there and books on astrophotography will contribute a chapter on the subject.

For me focusing is the hardest step when taking pictures.