What so you focus on?

[J13ERO]

I've tried out night sky photography a few times however they don't usually come out that great I think one of the issues I have is not having anything in the foreground so it's just a picture of stars... Boring (unless there's a galaxy etc)

When you have something in the foreground like a tree for example is it best to focus on that than trying to focus on the sky??

Thanks, James

 

[fred_bt]

Best to have enough depth of field that they're all in focus is the simple solution - which goes against the recommendation for opening up the lens as wide as possible to let the light in of course! So ideally place your foreground far enough away that it will still be in focus pretty much regardless. Getting a sharp focus on anything at night is a separate subject in itself, but the easiest way is to focus manually having noted where the lens itself thinks infinity is during daytime.

 

[J13ERO]

Best to have enough depth of field that they're all in focus is the simple solution - which goes against the recommendation for opening up the lens as wide as possible to let the light in of course! So ideally place your foreground far enough away that it will still be in focus pretty much regardless. Getting a sharp focus on anything at night is a separate subject in itself, but the easiest way is to focus manually having noted where the lens itself thinks infinity is during daytime.

Ok thanks for that so I need more distance from the subject! If I were to lower the aperture to get more in focus would that then require a longer exposure?

 

[simonblue]

Ok thanks for that so I need more distance from the subject! If I were to lower the aperture to get more in focus would that then require a longer exposure?

Yes,or you can change your ISO to an higher one,but that can bring problems with noise depending on your camera

 

[hollis_f]

Bear in mind that wide angles give large DoF. If you're shooting at 17mm on APS-C then even f2.8 will get everything in focus from around 5.4m to infinity.

 

[jimmyjamjojo]

Most people will do a composite, one for the stars and one for a foreground. You cant really afford to stop down any appreciable amount so dof will always be limited, and stars being point light sources are super fussy about focus, it has to be spot on.

 

[hollis_f]

Most people will do a composite, one for the stars and one for a foreground. You cant really afford to stop down any appreciable amount so dof will always be limited, and stars being point light sources are super fussy about focus, it has to be spot on.

You focus on the stars at infinity and everything from the hyperfocal distance to infinity will be within the DoF. For 17mm on FF at f2.8 the hyperfocal distance is 3.4m.