How to achieve proper focus of stars at night?

[haring]

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?

[sdwilsonsct]

Use a very bright star or planet? You can use one anywhere in the sky and then move the camera to your subject. Works for me.

[melchiorpavone]

I manually focus at infinity and the stars are out of focus.

Then the camera or lens is out of adjustment. See a repair shop!

[Ken Bennett]

Hmmm, depends on the camera and lens. Many modern lenses focus past infinity, and it's difficult to find the exact infinity focus point.

I use live view, at the highest ISO, with everything set to manual, and I can always find something on which to focus in the sky.  Then tape it down!!

[NancyP]

Aim camera at field containing very bright star. Turn on Live View, adjust exposure so stars show up on live view, magnify 10x or however far you can magnify your particular camera's Live View, focus on that bright star.

[Jeremy Roussak]

Aim camera at field containing very bright star.

I'd suggest not picking the sun, though 

Jeremy

[Dave Pluimer]

Aim camera at field containing very bright star. Turn on Live View, adjust exposure so stars show up on live view, magnify 10x or however far you can magnify your particular camera's Live View, focus on that bright star.

This ^^^ Put it in Manual focus and then gaff tape the focus ring to the lens barrel so it doesn't move. So long as you stay at the same f/stop and focal length, it should be set. Always good practice to verify it every so often if you are out for a long shoot.

[Slobodan Blagojevic]

How about hyperfocal distance?

[Dave Pluimer]

How about hyperfocal distance?

I've had nothing with bad luck using that. I learned that I'll need to focus stack if I want some foreground sharp as well as the stars.

[Slobodan Blagojevic]

... I manually focus at infinity and the stars are out of focus...

How's that possible? If by "manually focusing at infinity" you meant turning the lens' focusing ring all the way to the end, than yes, it is possible to have it out of focus, because many modern lens rings go beyond infinity (for a different reason). Try focusing using the infinity mark or hyperfocal distance, rather than turning the ring all the way, and you should be fine. Unless, of course, your lens or camera is out of alignment, as someone already noted.

[mjrichardson]

No offence but why are you waiting until 1am to find out where infinity is on your lens? You just need to understand your equipment, focus at infinity in the daylight and look at where it is on the lens barrel, mark it or do as I do and remember how far back from the lens stop you have to turn. Infinity is infinity, the time of day doesn't matter!

[bill proud]

A couple suggestions.

Focus on an infinity point before the sun sets and leave the camera at that position.

Bring a good flashlight and use it to focus at an infinity point.

[melchiorpavone]

How's that possible? If by "manually focusing at infinity" you meant turning the lens' focusing ring all the way to the end, than yes, it is possible to have it out of focus, because many modern lens rings go beyond infinity (for a different reason). Try focusing using the infinity mark or hyperfocal distance, rather than turning the ring all the way, and you should be fine. Unless, of course, your lens or camera is out of alignment, as someone already noted.

Maybe we need to know which lens and camera are being used here.

Some telephoto lenses have focusing rings that turn past infinity to allow for thermal expansion. See the photo, below, of the 350mm Telyt-R. I own this lens.

[Torbjörn Tapani]

With some lenses (Nikon 14-24 comes to mind) it is impossible to use the scale on the lens barrel or by touch. Focus just a tiny bit wrong and it will show at f2.8. It's literally within 1mm on the ring for accurate focus. Liveview and a bright star or planet works. The moon or street lights also works. There is usually a button that will turn up the brightness in liveview without changing exposure settings. Not zooming all the way in works best for me.

[Misirlou]

An important point is being missed here. Lenses contract and expand with temperature changes, enough that stars can be way out of focus from one minute to the next. This is why lenses have to allow for focus beyond infinity at normal temperatures. Once it starts getting cold at night, there may be significant focus difference.

People who do astrophotography with telescopes are plagued with focus problems due to thermal issues. Most serious astrophotographers I know use some form of temperature compensating focuser. Lots of options, but the best seem to require sensor/focus motor feedback loops.

A typical DSLR won't be used at such extreme magnifications that you'd need to refocus during a shot. But you'd certainly want to focus at the shooting temperature, probably right before shooting.

[melchiorpavone]

An important point is being missed here. Lenses contract and expand with temperature changes, enough that stars can be way out of focus from one minute to the next. This is why lenses have to allow for focus beyond infinity at normal temperatures. Once it starts getting cold at night, there may be significant focus difference.

People who do astrophotography with telescopes are plagued with focus problems due to thermal issues. Most serious astrophotographers I know use some form of temperature compensating focuser. Lots of options, but the best seem to require sensor/focus motor feedback loops.

A typical DSLR won't be used at such extreme magnifications that you'd need to refocus during a shot. But you'd certainly want to focus at the shooting temperature, probably right before shooting.

I showed a photo of such a lens, with an infinity mark well short of the 'stop'.

[luxborealis]

As a starting point, focus during the day at an infinity point, but make sure the day is a cool one to reduce the effect of lower temps at night. Mark the focus point precisely. Voilà.

[robdickinson]

If you have 'live view'

switch lens to manual focus
Set exposure simulation on
set to ISO 3200, lens wide open (not that this matters right now) 30 seconds
take camera off tripod
switch on live view
set lens close to infinity using scale
zoom to 10*
point at a bright star
wave around a bit until you see bright star on LCD
Adjust focus back and forth until you have the best point
Place back on tripod without knocking focus

Repeat later when needed.

[Jonathan Ratzlaff]

With a telephoto lens, some cameras will autofocus on a planet such as Juptiter.   This is one place were you don't want to have autofocus associated with the shutter button.  Manual focus lenses I focus on a distant object as far away as possible and take test pictures, then mark the best point of focus.  Some of the samyang(bower) lenses have good image quality but poor infinity focus so testing is required.