Auto Focus Issue - shooting into bright light

[Grimes]

Hey all,

I was trying to do some "high key" photos today, and was shooting a subject with the sun streaming in from between trees behind him. (About 5PM today, so I wasn't shooting right into the midday sun, but it was still bright.)

Now AF supposedly locked onto him, using the second leftmost AF dot on a RebelXT (shooting portrait orientation). However, when I look at the pictures, his face came out soft and out of focus. This is with Flash, no assist beam, f/2.8 on the nifty Fifty, 1/100th sec exposure, ISO 400.

Does bright light cause AF to become inaccurate for some reason? Thanks in advance!

[Jamesino]

Could you perhaps post some example pictures?

[Grimes]

sure, hold on a sec - here you go. BTW, I see the darn flash in his glasses, I have to practice more! And spend for an external flash, lol.

http://mysite.verizon.net/vze24c8d/alex/misc/pics/jon_high_key.jpg

[PhotosGuy]

Now AF supposedly locked onto him, Was that One shot, AI Focus, or AI Servo?
At f/2.8, one of you might have moved a bit.

[Grimes]

Was that One shot, AI Focus, or AI Servo?
At f/2.8, one of you might have moved a bit.


Hi PhotosGuy,

It was set to one shot....I've taken photos with this lens before at 2.8, and it should have been way sharper.

Perhaps he did move.

I have heard that sometimes the points other than the center one are less accurate - any truth to this? Thanks.

[johnny0415]

This happens to me too whenever I take portaits with the sun lighiting up the subject from behind. My guess is there is a loss of contrast when you introduce direct sunlight and this loss of contrast makes AF really hard for the camera. I use an XT also btw.

[PhotosGuy]

I have heard that sometimes the points other than the center one are less accurate - any truth to this? I haven't noticed it with the 20D & I have focus point choice set on the joystick, so I use off center points a lot. It might be true for people with slower lenses, though.
Stay away from AI Focus. Some people have problems with it:
AI Servo or AI Focus? Advice needed please (http://photography-on-the.net/forum/showthread.php?t=452501)

[Grimes]

This happens to me too whenever I take portaits with the sun lighiting up the subject from behind. My guess is there is a loss of contrast when you introduce direct sunlight and this loss of contrast makes AF really hard for the camera. I use an XT also btw.


Ah, thanks for the reply Johnny. I'll be sure to double check the focus, or use manual focus next time!


I haven't noticed it with the 20D & I have focus point choice set on the joystick, so I use off center points a lot. It might be true for people with slower lenses, though.
Stay away from AI Focus. Some people have problems with it:
AI Servo or AI Focus? Advice needed please (http://photography-on-the.net/forum/showthread.php?t=452501)


Cool, thanks for the info and the link. I never use AI Focus though - only rarely do I even use Servo.

[yogestee]

This image exhibits heaps of flair from shooting into the sun.. Flair can make an image appear soft..