Focusing in the Dark

[Chainsaw_Willie]

This is probably a stunningly basic beginner question, but I haven't quite figured it out yet...

When it's too dark for autofocus to work and the subject is too far away for the focus assist light to work, how do you get accurate focusing? It's really hard to tell through the viewfinder in dim light when things are sharply in focus.

Specifically, when taking star shots. My lenses allow focusing beyond infinity, so I can't just crank the focus ring all the way over, can I?

[altabird92]

you can crank the focus ring over, or
use a flash light to light up a bush
using quick release plate on a tripod, remove camera and autofocus
it should focus to infinity if the bush is far enough
hold the shutter half down and put camera back on tripod,
then shoot with a piece of cardboard in front of the lens to keep the focus
once you shoot, remove the cardboard

[Tippster]

Your lenses need adjusting, then.

Your camera certainly isn't "focusing" on stars, so just put it in Infinity. If the shot is blurry it's more likely to be camera shake than a focal issue, unless - as stated above - your lenses are whack.

When you focus manually at infinity and full zoom are distant objects out of focus? Do they come in focus when you back off a little?

[Chainsaw_Willie]

Your lenses need adjusting, then. ...
When you focus manually at infinity and full zoom are distant objects out of focus? Do they come in focus when you back off a little?

Yes, that is the behavior, but not all of my lenses do this.

I was out backpacking again this weekend (thus the lateness of this reply) and the lens I took this time was in focus on distant objects when turned all the way to infiniti.

So, if a lens is out of focus when cranked all the way to infiniti but comes back in focus when backed off a little bit, does that lens need adjusting? I thought I had read somewhere a long time ago that lenses have this "beyond infiniti" focusing thing built into them to accomodate expansion and contraction in cold and hot temperatures..???

[jce338]

bump. curious about this.

[bklyn]

As far as your camera is concerned, stars are at infinity. Back off the Buzz Lightyear setting and you should be fine. Most
lenses have all the little numbers and symbols on the side to assist you in the setting.

It's also difficult to get low light photography right if the camera is not stabilized. If you are shooting handheld, you won't be able to tell with accuracy why your photos are blurry.

[Chainsaw_Willie]

Yes, I shoot on a tripod in very low light/at night.

I decided to look through my lens quiver and see how many/which lenses exhibit this behavior. The list indicates whether a given lens is focused at infinity when the focus ring is cranked all the way in one direction or not.

18-35 f3.5-4.5 -- focused
24-70 f2.8 -- not focused
24-120 f3.5-5.6 -- not focused
55-200 f4-5.6 -- not focused
50mm f1.8 -- focused

The 55-200 doesn't even have any focus marks printed/engraved on it. The other lenses do and it appears they're in focus at infinity when the indicator mark is pointing to the center of the infinity symbol.

As for the 55-200, I'm just going to make marks on it myself. Or, I might not bother as it's not going to be in the quiver for much longer - trading it for something longer.

This picture was taken with the 55-200 and it's what got me looking into this. It's a great picture, except it's slightly out of focus even though it looked focused through the viewfinder:

http://i114.photobucket.com/albums/n...escentmoon.jpg

[Tippster]

A split circle focusing screen would have helped in that picture. hold the camera horizontally, use the split circle to focus on the trees (or the moon) then compose the shot the way you want.

If you think you'll be doing a lot of manual focusing I would def. go with the split circle replacement screen.

[Chainsaw_Willie]

Hey, that's pretty neat. Thanks for the tip!

[kalisto]

Bumpity bump...

Was out shooting last night in the city (1:00 am ish), so I was having the same problem...

I was shooting relatively close, I was thinking maybe a headlamp would help...

Other than replacing the screen, any tips for focusing in the dark?

[kidwoo]

I used to just carry a flashlight.

find it, focus it, turn the light off

[summit]

The list indicates whether a given lens is focused at infinity when the focus ring is cranked all the way in one direction or not.

18-35 f3.5-4.5 -- focused low zoom ratio wide DoF
24-70 f2.8 -- not focused short DoF zoom
24-120 f3.5-5.6 -- not focused large zoom ratio lens
55-200 f4-5.6 -- not focused shitty lens, no indicator, not made to MF.
50mm f1.8 -- focused (it's a prime!)The

55-200 doesn't even have any focus marks printed/engraved on it. The other lenses do and it appears they're in focus at infinity when the indicator mark is pointing to the center of the infinity symbol.

Above are the reasons why! Zooms, particularly large ratio or low DoF zooms have focus changes during zoom. There must also be additional travel for variances in manufacturing and temperature. Very few AF lenses are truly focues to infinity if focus is cranked all the way over.

[Doc Green]

I'm focused at infinity here with f.9, 30 seconds, iso 1600. Camera shake is big issue, a little goes along ways.

[Fuzz]

Specifically, when taking star shots. My lenses allow focusing beyond infinity, so I can't just crank the focus ring all the way over, can I?

I've been getting into astrophotography ([ame="http://www.tetongravity.com/forums/showthread.php?p=2433292#post2433292"]first attempts here[/ame]), and everything I've read and my meager experience so far support what you said. You cannot crank the focus all the way because it'll focus beyond infinity.

I've found two options. I usually shoot with an 18-200mm lens, so zoom fully to a bright star (e.g. Vega), and focus manually until the star is the sharpest through the viewfinder. Another option is to get a 2x magnifier (which is what I ended up doing). It's a little lens that attaches to the viewfinder and gives you a 2x view of the center of the viewfinder.

Here are some star shots of mine from early this morning:

[Fuzz]

Check out this page for star focusing: http://www.astropix.com/HTML/I_ASTROP/FOCUS/METHODS.HTM

I'm going to try creating a Hartmann Mask (recommended by many) for myself this week.