How to focus stars

superpires · Sep 6, 2015

Hi, I'm new to this forum

. Yesterday night I tried to shoot stars for the first time. I read a lot of articles about it and wanted to give it a try. After shooting for an hour, I realized the stars are out-focused, actually, nothing is in focused. I heard people said I should use a flashlight and focus the nearest object. But what if there is no any other objects near me? I can't see anything through the viewfinder. Really need some advice on it, Thanks!

This is what I got Thank youuuuuu

jsecordphoto · Sep 6, 2015

None of those articles mentioned how to find correct focus?

If your camera has live view, use that and zoom in on a bright star, then adjust focus until the star is a small pinpoint of light. If you don't have live view, I suppose you could just look during the day to where "true" infinity is with your lens, then keep a note of that for once it gets dark.

Designer · Sep 6, 2015

superpires said:
I heard people said I should use a flashlight and focus the nearest object.

Probably not. I think you misunderstood. Not the nearest, but rather more like the farthest.

Don't let the camera try to find focus, because as you have discovered, it will not "see" the stars. Turn off the auto-focusing feature, and focus manually, and set your lens to "infinity". Note; the markings on the lens barrel may not be accurate enough to focus on the stars, so do what jsecordphoto has written above.

NancyMoranG · Sep 6, 2015

Guys, should OP also use a higher ISO than in shot above to brighten things up a bit? (If they want more light!)
Just learning here..

TCampbell · Sep 6, 2015

Four things:

1) Take your time and carefully focus. Increase the magnification on your view screen to max to make it easier to tell when your image is focused on the sky. It doesn't matter what object in the sky you use to focus because if anything is in focus, then everything is in focus (the focus on the moon vs. the focus on a star many light years away is identical.) On a telescope I use a Bahtinov focusing mask.

If your camera does exposure simulation (and I think your Sony camera does) then cranking up the exposure just while you are focusing can help you see the stars. Don't forget to return exposure to a more reasonable setting when you take the shot.

2) Technically, all stars are so very far away that they should expose merely as a single point of light. The reality is that due to the wave nature of light, that's not what really happens. They focus to something called an Airy Disk (named for the astronomer who discovered them). So you'll never really get a star to be truly "pinpoint" -- but you can get close.

3) The atmosphere itself will tend to blur the stars. Astronomers refer to this as "seeing" conditions. I use the analogy of a coin on the bottom of a pool of water. If nobody is making waves on the pool, then you can see the coin quite clearly -- and use binoculars and you might even be able to read the date on the coin. BUT... if someone starts making waves, the coin is going to distort constantly. You might be able to spot the coin, but you'll have an incredibly difficult time trying to read the date. The sky actually does this to us... it causes the stars to wobble and distort by tiny amounts. This is what causes stars to twinkle and also appear to shift colors as they twinkle. The technical name for this is "atmospheric scintillation". But when you see twinkling stars, that means the stars are distorting. Those stars are going to record as even larger blurry spots -- regardless of how good incredibly careful you were when focusing. There are some astronomy websites we use to check the "seeing conditions" but basically if there's either a high or low pressure system within 200 miles of your location and/or if the jet-stream is passing within 200 miles of your location then the seeing conditions are degraded. It can actually be a dead calm on the ground but have horrible seeing in the upper atmosphere -- so you can't just go by whether or not it is windy.

4) Photoshop is your friend. There are a few techniques that imagers use to sharpen the image. One is the "unsharp mask". But note that there's a slider on that tool called "threshold". That's the amount of contrast difference necessary for Photoshop to think this is an area where you'd like to apply sharpening. Increase that just slightly (set it at maybe 1-3) and you'll notice that instead of trying to sharpen the entire image (which generates "noise") it leaves the flat areas of the image alone and only applies sharpening where there's a contrast difference.

Also, there's a tool called the "High Pass Filter" that works well. This tool is a little less straight-forward to use but you can do a search for YouTube video with terms like "astrophotography high-pass filter" and it will probably find several tutorials on how you can use that filter to tighten up the image.

Good luck!

KmH · Sep 6, 2015

The stars in your photo are not out of focus.
They are elongated into short streaks because the Earth rotates on it's axis once every 24 hours.
Exposures of stars from 12-15 seconds or longer without the camera being moved to counter the Earth's rotation will make 'star trails'.

how to avoid star trails in photos

evenflowphotos · Sep 10, 2015

Maybe I missed them but could you post the settings that you used to take the photograph please

petrochemist · Sep 10, 2015

KmH is right that you have the starts of star trails in your shot. His comment on the acceptable exposure times is too simplistic however.
Star trails are seen more rapidly with longer focal lengths (and more when viewing further away from the pole star). There is a rule of thumb to help avoid star trails. IIRC its known as the 600 rule, and states to avoid star trails limit exposures to 600/focal length in seconds. (Some work to 500/focal length) With a fish-eye lens 60s may be OK, while my mirror lens would show trails in about 1 second. To deliberately sow star trails you need exposures considerably longer - generally 10x or more.
FWIW I think your focusing is better than I've achieved in most (or even all) of my attempts at start shots, though probably not quite as good as your lens CAN manage.

BananaRepublic · Sep 10, 2015

Your focusing in the posted shot seems ok just try to be in as dark place as you can and switch off lights. Admittedly I know nothing about sony cameras and I assume TC got your camera brand from some source but my impression is that their baffling you with jargon.
This how i do it i have a nikon d5100:

At night: if you have live view use switch to that mode and manually focus on a bright star using the focus ring. auto focus has to be turned off and left off.

Before dark or before its pitch black : It may be bright enough for the camera to autofocus on something far away if it does this then switch off autofocus from then on in.

How to avoid stair trails: the earth is always moving but a 30 second or less shutter should reduce the effect.