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DPChallenge Forums >> Individual Photograph Discussion >> Uneven focus (not just DoF)
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AuthorThread
 01/11/2006 04:58:55 PM · #1
First of all this is nothing like any of my competition entries and is not a âspoiler.â

I was very frustrated as I was working on this image.



What bothered me was the fact that the stars and tree on the right were blurred and the stars and tree on the left were sharp(er). Now... I understand I had my focus off on the trees... but the stars? Why are they not uniform? I assume the stars on the right are not significantly closer and that I did not shake just the right side of the camera.

Theory 1: The raising sun which is slightly to the right is having a blurring effect. UV light perhaps. And the earth is protecting the left side of the image.

Theory 2: I have a subtle optics mis-alignment or error that is causing the effect.

Thoery 3: Optical illusion since that side is brighter color.

Any ideas why this happened?

As a side note... How DO you focus on something in total darkness? I was unable to see the tree through the viewfinder and the AF was useless.
 01/11/2006 05:04:49 PM · #2
What settings did you have for the shot?
 01/11/2006 05:06:16 PM · #3
Rotation of the earth, Im guessing the stars on the right were farther south than the ones left. It shows 30 seconds of Exposure on the photo.
 01/11/2006 05:06:19 PM · #4
Collection: Portfolio
Camera: Canon EOS-10D
Lens: Canon EF 28-135mm F/3.5-5.6 IS USM
Location: Causeway Alabama
Date: Jan 5, 2006
Aperture: f/3.5
ISO: 400
Shutter: 30 sec

Message edited by author 2006-01-11 17:06:42.
 01/11/2006 05:07:30 PM · #5
Aperture: f/3.5 might be the problem, but I'll let the experts confirm it.
 01/11/2006 05:08:33 PM · #6
it looks like it was windy and the camera moved...I'd be willing to bet that's what happened...or the stars are from earth's movement, and the tree blurriness is from the wind.
 01/11/2006 05:09:20 PM · #7
Originally posted by MQuinn:
Rotation of the earth, Im guessing the stars on the right were farther south than the ones left. It shows 30 seconds of Exposure on the photo.


Ahh... good thought. I was shooting East North East so the stars on the left would have been more northernly in position.
 01/11/2006 05:10:13 PM · #8
Did you use a tripod with the "IS" on?
 01/11/2006 05:12:58 PM · #9
Its the sun/brightness on that side that makes them seem blurry. A good example is an old camoflauge effect used in ww1 or ww2 where planes trying to spot or bomb submarines would put bright lights on their wings, the lights help make the plane blend in with the sky. Same thing here the rising sun making the sky brighter there is causing the stars to start to blend in. If you had a strong enough telescope you could see stars durining the day but it more difficult because the light makes them blend in with the sky.

*edit to fix spelling*

Message edited by author 2006-01-11 17:14:40.
 01/11/2006 05:13:12 PM · #10
Originally posted by dpaull:
it looks like it was windy and the camera moved...I'd be willing to bet that's what happened...or the stars are from earth's movement, and the tree blurriness is from the wind.

I will agree I just put the picture in PS/CS and looked at it at 300%. To me it looks like a slight breeze judging by the trees and grass. Also there is movement to the left-right like camera shake even on the lights on the ground. This tells me that possibly you used a tripod but pressed the shutter instead of using a remote or timer, is that correct?

I also would of would of went with a different aperture setting and a lower ISO if possible.
 01/11/2006 05:14:10 PM · #11
Originally posted by Brent_Ward:
Did you use a tripod with the "IS" on?


IS is on... the camera is sandbagged on top of a stable 4-point ladder to get it above the reeds.

dpaull: the trees were blowing slight... and I also was just plain out of focus with them. :( It's tough to focus what you can't see :)

Southern: I used delay trigger to keep from hitting the button, but therefore couldn't use the mirror lock (I've lost my remote trigger).

Message edited by author 2006-01-11 17:16:38.
 01/11/2006 05:16:56 PM · #12
Originally posted by ShotMD:
Originally posted by Brent_Ward:
Did you use a tripod with the "IS" on?


IS is on... the camera is sandbagged on top of a stable 4-point ladder to get it above the reeds.

dpaull: the trees were blowing slight... and I also was just plain out of focus with them. :( It's tough to focus what you can't see :)


Using IS while the camera is on a tripod can cause problems. As noted in the lens manual, the IS should be off if using a tripod.
 01/11/2006 05:17:43 PM · #13
Stars will move across the sky during a 30 second shot. Depending on the area of the sky they're in, some stars will move more than others.

Also, a tree will move around in the wind as well.
 01/11/2006 05:20:26 PM · #14
Originally posted by ShotMD:
Originally posted by Brent_Ward:
Did you use a tripod with the "IS" on?


IS is on... the camera is sandbagged on top of a stable 4-point ladder to get it above the reeds.

dpaull: the trees were blowing slight... and I also was just plain out of focus with them. :( It's tough to focus what you can't see :)

Southern: I used delay trigger to keep from hitting the button, but therefore couldn't use the mirror lock (I've lost my remote trigger).


Hmmmmmmmmmmmmmmmmmmmm what about hyper distant
01/11/2006 05:26:32 PM · #15
I don't know if this is the best way or not, but I throw it out for consideration -

When I'm shooting something I can't see - I remember shooting in a cemetary after dark for a challenge - I set my aperature at it's smallest (smallest aperature, largest number, so I was shooting at 22 in the cemetary) to maximize my DOF so if I'm off in my focus guess, the DOF will make up for it.

For your shot, I would have manually focused to infinity, backed it off a little (1/8 of an inch or less) and stopped down to 22 - 32 depending on the lens and opened it longer to increase tha DOF - but increase the star blurs - hard choice if you want your stars rock solid.

Seems to work for me - is there a better way?
 01/11/2006 05:31:42 PM · #16
The stars move, enough that in a 30 second shot like that you'll get some slight trails.



As to infinity focus, most lenses have an infinity symbol, when you line that up with the focus point on your camera, then you are focused on infinity, or close to it. For many zoom lenses, this is not the same as turning the focus all the way to the extreme.

I typically use a flashlight to focus on things at night - I'll shine the light on them, focus and then switch to manual to recompose.

Also it is useful at night to shoot a highest ISO 'preview' shot, to help work out the correct exposure then divide and multiply by 2 down to the shutter speed and aperture you want.

For night shots, depending on your camera, an ISO of 200 or 400 and an aperture of F4 or f5.6 gives good star trails.

Message edited by author 2006-01-11 17:33:18.
 01/11/2006 07:36:30 PM · #17
Gordon,

what speed where those shot at? They are great, now I want to try star trails.
 01/11/2006 11:54:25 PM · #18
Originally posted by digitalknight:
Gordon,

what speed where those shot at? They are great, now I want to try star trails.


F4 @ 45 minutes for the second one, about 20 minutes for the first one.
 01/12/2006 12:00:41 AM · #19
To the OP, there's no doubt that what you're seeing is star trailing. Given the direction you were shooting the pattern makes perfect sense, and he amount is about right for that exposure time, assuming you were shooting at the wide end of that lens.
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