Can u AF Lock and recompose on a DSLR?

[simplicitee]

I'm using a canon 40D, and its become a habit to halfpress the the shutter button and then recompose my picture.

But it seems to me that sometimes the focusing is a little off.

Any ideas?

I was always under the assumption that the "AF-lock and recompose" is a common practice. Is it?

[Rashkae]

Originally Posted by simplicitee I'm using a canon 40D, and its become a habit to halfpress the the shutter button and then recompose my picture. But it seems to me that sometimes the focusing is a little off. Any ideas? I was always under the assumption that the "AF-lock and recompose" is a common practice. Is it?

Yes it is. But if you're using a large aperture, you need to consider how your plane of focus shifts when you recompose.

[Anson]

You can move left & right (when recompose) but try not to move front & back...

[aryanto]

Originally Posted by simplicitee I'm using a canon 40D, and its become a habit to halfpress the the shutter button and then recompose my picture. But it seems to me that sometimes the focusing is a little off. Any ideas? I was always under the assumption that the "AF-lock and recompose" is a common practice. Is it?

yes it is, this is an old technique.

First you must be stationary.
Your subject should not move too much.
Your DOF is not too thin (eg: use F3.5 and above you should be OK for portrait of a single person).

[tangklrb]

it happened to my D60 too sometimes when i recompose, it focus on the final object that it's pointing on.

[Rashkae]

Originally Posted by tangklrb it happened to my D60 too sometimes when i recompose, it focus on the final object that it's pointing on.

Make sure you're not using continuous AF.

[Snoweagle]

The best bet to ensure that your subject stays in focus even after recomposing is to select the AF point closest to the focused part so that movement is minimal.

[aryanto]

this cannot be used for sports by the way, unless the sports you are talking about is finishing or chess.
you can practice this with statues though, cos the only thing moving will be you.
just make sure you have enough DOF, and shoot in the day.

I believe I shoot this with focus (AF) & recompose

[DeSwitch]

i reconfigure my AE-lock button to be my AF lock so now I focus with my thumb and forget about the 1/2 press. Need a bit of getting used to but after a while, it become 2nd nature.

[simplicitee]

Originally Posted by DeSwitch i reconfigure my AE-lock button to be my AF lock so now I focus with my thumb and forget about the 1/2 press. Need a bit of getting used to but after a while, it become 2nd nature.

Good idea!

Thanks everyone....my problem may possibly be because i was using AI Servo...

[Anson]

Originally Posted by simplicitee Good idea! Thanks everyone....my problem may possibly be because i was using AI Servo...

No wonder......

[ST1100]

Originally Posted by simplicitee Good idea! Thanks everyone....my problem may possibly be because i was using AI Servo...

Cannot be lah, if you're on servo it won't be "a little off", it will be way off, focusing instead on the background. In the example above, the person would be in focus while the foreground would be blurred out.

[Override2Zion]

Originally Posted by Snoweagle The best bet to ensure that your subject stays in focus even after recomposing is to select the AF point closest to the focused part so that movement is minimal.

This is very good advice , when using the center AF point to focus and recompose, you may not see the difference . When you're shooting wide open using larger apertures, the focus difference may be more obvious. Best bet is to use the focus point nearest to the subject to minimize movement during recomposition.

[simplicitee]

Originally Posted by ST1100 Cannot be lah, if you're on servo it won't be "a little off", it will be way off, focusing instead on the background. In the example above, the person would be in focus while the foreground would be blurred out.

Really meh? Haha... i usually set to AI Servo lei....maybe i was lucky then....but will switch to "one shot" from now on.

Originally Posted by Override2Zion This is very good advice , when using the center AF point to focus and recompose, you may not see the difference . When you're shooting wide open using larger apertures, the focus difference may be more obvious. Best bet is to use the focus point nearest to the subject to minimize movement during recomposition.

Is this this where Nikon's 51 AF points (not sure if i got the number correct) is better than Canon's 9 point AF?

But then again, selecting that 1 point from 51 possible points can be quite time consuming.....

[Snoweagle]

Originally Posted by Override2Zion This is very good advice , when using the center AF point to focus and recompose, you may not see the difference . When you're shooting wide open using larger apertures, the focus difference may be more obvious. Best bet is to use the focus point nearest to the subject to minimize movement during recomposition.

When shooting infinity, doesn't matter as everything's in focus but the difference is very obvious when shooting close-up.

[crimsonseas]

Originally Posted by simplicitee Is this this where Nikon's 51 AF points (not sure if i got the number correct) is better than Canon's 9 point AF? But then again, selecting that 1 point from 51 possible points can be quite time consuming.....

Not really. Having moved from the D80 to the D300, I would say that the point selection doesn't really suck up much additional time. Or maybe I've gotten used to it...

[alvin]

Originally Posted by simplicitee Really meh? Haha... i usually set to AI Servo lei....maybe i was lucky then....but will switch to "one shot" from now on. Is this this where Nikon's 51 AF points (not sure if i got the number correct) is better than Canon's 9 point AF? But then again, selecting that 1 point from 51 possible points can be quite time consuming.....

The last 2 times I tried the D300, I specifically tried the 3D AF tracking; it was able to "track" i.e. put a AF point the my subject, recomposed, and the AF point would follow. I can't believe how well it works. I'm currently waiting for the D300 replacement so I can get my D300 once all the ppl dump the d300 for the latest and best =)

Till then, my d200 still kicks ass