Using Auto-Focus at night..

[skywalkerbeth]

Hi everyone

I just got back from a great trip to Europe with my Mom. I lugged
along my new spiffy (and thankfully, ultralight) tripod.. and took
it out exactly once.

I can't say I am entirely happy with the results, and mostly because
of the focus. How can you auto-focus at night time (or even
manually)?

The subject photo taken from a balcony high up above Lake Como,
focusing on the far shore after dark. The lights on the other side
are kind of fuzzy. I'd say it's no less than a mile away, but the
camera just doesn't seem to know where to focus and manually focusing
when it's dark is tough too.

I also seem to find that setting the focus point on "full infinity"
doesn't seem to work, even though clearly it's a mile or more away.

Any thoughts? is it possible my lens needs to be calibrated?

I've seen some stellar night photos where everything is quite crisp
and clear, and I just don't know how to achieve that yet.

Here is the subject photo, it also looks a little grainy, which is weird because it was ISO 100.


http://farm4.static.flickr.com/3056/2578165236_2e7438df0b_b.jpg

[Pete]

On most lenses, "full infinity" is actually past infinity. So putting the focus on the end-stop will always give you out of focus images.

The 30D should have been able to focus on the lights on the other side of the lake there. So, pointing the camera at them, focusing, and then tilting the camera back up again should have done the trick for you.

[Stocky]

If its soft part of the problem might have been your tripod setup. You said that it is "ultralight" which isn't exactly what you want in a tripod. What was the EXIF on this one?
Oh, and it looks like someone sneezed on your sensor.

[TheHoff]

She bought a killer Gitzo, so the problem isn't the legs.

The "grain" is noise from long exposures. Try the custom function that turns on long-exposure noise reduction (and don't underexpose!)

[PhotosGuy]

The "grain" is noise from long exposures. True, but the goobers are sensor dust.
Use AF to focus. Then put your lens on manual.
Or use C.Fn-13 (1) to put the focus points on my joystick (multi controller) which makes it easy to switch when things are moving fast or other situations where I need an off-center point.

[skywalkerbeth]

great advice gentlemen, thanks! back to the owner's manual...

when you say sensor dust - how the heck do I get rid of it? it's also a brand new lens (camera is almost two years old though...)

http://www.flickr.com/photos/skywalkerbeth/2578165236/in/set-72157605258259622/

Exposure: 30 sec (30)
Aperture: f/18
Focal Length: 24 mm
ISO Speed: 100
Exposure Bias: 0/3 EV

[TheHoff]

I don't think you needed f/18 to get sharpness throughout the frame. Dropping to f/8 or f/11 would've cut the exposure time by quite a bit which would've sharply reduced the noise from the long exposure. Also, I'd shoot a bit earlier in the evening so you get some color in the sky (I know sometimes that isn't possible when traveling and only in one place for a short while.)

oh yea, sensor dust... Remove the lens, turn the camera so the mount is facing the ground, put it in self-cleaning mode, and use a blower.

http://www.bobatkins.com/photography/tutorials/sensorclean.html

[PhotosGuy]

I don't think you needed f/18 to get sharpness throughout the frame. Dropping to f/8 or f/11... ...would reduce the effects of the dust, too.
Some personal views on Sensor cleaning. (http://photography-on-the.net/forum/showthread.php?t=184448)

[skywalkerbeth]

Thanks, I will sort this out when I get home.

[Cody21]

snip .... oh yea, sensor dust... Remove the lens, turn the camera so the mount is facing the ground, put it in self-cleaning mode, and use a blower.

http://www.bobatkins.com/photography/tutorials/sensorclean.html

I think the OP said he has a 30D ... which doesn't have "self cleaning" (that's my body as well)... He'll need to have it cleaned, or just bite the bullet and learn the technique to clean it himself (and save money/time in doing so) as you so well pointed out in that link..

[tdodd]

Use the DOF calculator here - http://www.dofmaster.com/dofjs.html - to look at the sort of DOF you could get at various focal lengths, subject distances and apertures. As an example, if you had set focal length to 24mm and aperture to f/8, and then set focus to 13' - about 4m - you would have had a DOF covering from just 6'4" to infinity. That should have been more than enough for your scene.

You didn't even need anything in particular to focus on. You could have simply looked at the distance scale on your lens and set it to something around the 13' or 4m mark (not less than that). At f/8 instead of f/18 you would have avoided any diffraction softening and gained a much higher shutter speed. Good news all round.