How to achieve proper focus of stars at night?
I would like to take some photos of stars at night. I have found the location. No problem. I have to keep an eye on the alligators while I am doing this because the location is in the Everglades. No problem. 
The only problem I am facing is that I have hard time focusing at the stars because the viewfinder is black. (It is 1:00am at night after all.... ) 
I manually focus at infinity and the stars are out of focus.
I have tried to use the screen in video mode after increasing ISO. No luck. Even the screen on the back of the camera is dark so I am not be able to see the stars for proper focusing.
My question: How do you focus in total darkness? Did I miss something?
The only problem I am facing is that I have hard time focusing at the stars because the viewfinder is black. (It is 1:00am at night after all.... ) I manually focus at infinity and the stars are out of focus.
I have tried to use the screen in video mode after increasing ISO. No luck. Even the screen on the back of the camera is dark so I am not be able to see the stars for proper focusing.
My question: How do you focus in total darkness? Did I miss something?
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Remember, you just need to focus at infinity which is much closer than the stars; so one thing that works well is to focus on any lights on the horizon from a distant town or streetlight if there are any.
Another thing you can do is get your infinity focus when it's still light out by focusing on something off in the distance, then tape your focus ring down with some gaffers tape and put the lens in manual focus.
If all else fails, you might surprise yourself that if you stare long enough in your viewfinder that you can actually see the stars though it. Even with my bad eyes, I've discovered that I can just barely see the stars well enough to manual focus. It's a last resort, but I seem to be able to get good results that way.
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First things first, turn off Auto focus, AND turn off IS/VR image stabilization also. You are going to be on a tripod, and IS/VR must be off, and so must AF. But, once you are focused for infinity at night, you no longer have to worry about focusing all night long. Manual Mode as well, ISO 1600 or thereabouts.
One technique involves focusing on a far distant object at the far horizon during daytime, and then taping the lens barrel so it cannot move. This only works of course if you have a lens that has a rotating lens barrel offering manual focus. Most Canon and Nikon lenses do this, but some lenses do not offer a manual rotating lens barrel. SO you must focus electrically with either manual focus or autofocus.
If you are trying to shoot stars with lenses slower than f2.8 things get significantly harder, so I am assuming an f2.8 lens mounted on the camera and views through wide open. Old style mechanical lenses will not be wide open unless you have set them to their maximum aperture. But old style mechanical lenses work great for stars shots, since each step is done manually anyway.
Find a dark place, preferably without a bright moon, put your camera on the tripod and look for an area of brighter stars. Turn on Live View, and use Live View at a magnification of 5x or 10x to helps refine your focus with manual focus. One you have focus at 10x, turn of Live View and do not touch your lens barrel any longer.
If the stars are bright enough, some ( very few - my Lumix GH3 and Canon 1DX seem to sometime ) of the pro series cameras may be capable of auto focusing on a bright star - (an f1.4 or faster optic really helps here ) - more light is better - after grabbing AF, turn off the autofocus button on the lens or the rest of the evening.
Take your first shot at ISO 1600 25 seconds, f2.8 and see how your image looks.
With luck you should have something like this in the northern hemisphere f2.8 ISO 2000 25 seconds at 16mm focal length
In the southern hemisphere it will look more like this - f3.5 ISO 3200 25 seconds at 21mm focal length
Joel makes an excellent point that achieving visual confirmation of focus in the viewfinder does get a bit easier after you are fully dark adapted yourself, but this takes over an hour after sunset, and any bright artificial light will quickly degrade it again, if folks around you don't use good light discipline ( and they frequently don't ) Use a dim red LED light for your own night shot light to adjust your camera settings if you need to, this will be much less damaging to your own dark adaptation than a bright white LED light... Coast makes a nice dual LED light that offer a bright white when needed for trail finding, and a much dimmer red light useful for close up tasks when dark adapted. If you must use a bright light to fiddle with your camera, cover the bulb/reflector with your hand or fingers to decrease its intensity.
Try to keep your shutter speed less than 25 seconds or so for lenses with a focal length of 28mm or less. Longer focal length lens will need even shorted shutter speeds to not capture apparent star movement. Shorter shutter speeds are better when shooting stars, but try to keep ISOs less than 2000 if you can. Faster apertures are better, and f1.4 or f2 are preferred, but tend to be more expensive. There are some interesting f0.95 lenses ( totally manual lenses ) for m4/3 cameras that may offer the night shooter some shorter shutter speeds.
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