Night photography focus

[mlfodor]

Hello,

I'm new to photography and have a D90 for my first DSLR. I've read some books and taken an online course to learn how to use the camera. My problem is that I've been trying to take some night sky photos with extended exposure(bulb setting) but I can't get focused. I know the stars are up there but if the camera can't auto focus and I can't see to manually focus how do I get the shot? Or am I expecting too much.

Thanks,
Mike.

[kirbinster]

Well last I checked the stars were really really really far away -- some might call that infinity. So why not try just manually setting the focus to infinity. If you want to autofocus pick some other brighter and larger object that is far away, focus on it and lock the focus while you recompose on the stars.

[Federico Presti]

Well, probably the standard lens in your camera focuses "beyond" infinity, that means that if you turn the focusing ring all the way it won't really focus, you need to auto focus on a far object and lock it there. Trying to look through the viewfinder while your camera is pointed vertically can be a pain in the rear... night sky photos can be a real challenge

[Boyan]

Hi Mike, autofocus needs contrast in order to achieve focus. With the night sky, finding sufficient contrast for the camera to be satisfied can be tricky. Since you're using bulb anyway (and presumably tripod), forget the autofocus, switch your lens to manual, turn on your live view, zoom in all the way on the screen and manually focus to perfection.

[LeeR]

I did a little checking and learned that the camera you have, Nikon D90, has a hyperfocal mode. Years ago this was a very popular method of shooting but is rarely discussed these days. The technique uses information from the manufacturer that states that if your aperture is set for, say, f16 and your focus is set at 20 feet, then everything from 8 feet to infinity will be in focus. This was a huge benefit to sports and people photographers who depended on timing for success. Set the shutter to the right light level and you had nothing to do but compose the image and press the shutter.
The technique has fallen out of use largely because of zoom lenses. Each focal length will have a different setting making the calculations rather complex. However, this is child's play for your camera's onboard computer. Set the camera to Hyperfocal Mode and regardless of the zoom or aperture, the camera will figure out where it needs to be focused to maximize the area in focus, including infinity.

[Sterling]

AFAIK, there is no mode on the D90 that will automatically focus at the hyperfocal distance.