Using Auto Focus

donkeymusic

donkeymusic

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Carlo
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Morning,

i have been using auto focus for portrait work and moving the focus point to the head or the eye for closes up.

But read somewhere the other day and cant find what i was reading so wondered if from my poor desciption someone could help me?

bascially the article was about using auto focus to set the focus then to reset the composition, if i was to then move the camera to reset the composition does this not alter the auto focus?

any ideas?

cheers
 
I think it was probably about using the focus lock when shutter is half pressed...

For example for a portrait you would put your focus point on the eyes, half press the shutter to lock the focus then move the compostion whilst still holding shutter then fully press to take the shot...

You can as you say move the focus point around especially for static portraits...

:thumbs:
 
markw08 said:
I think it was probably about using the focus lock when shutter is half pressed...

For example for a portrait you would put your focus point on the eyes, half press the shutter to lock the focus then move the compostion whilst still holding shutter then fully press to take the shot...

You can as you say move the focus point around especially for static portraits...

:thumbs:
Click to expand...

Either I am picking you up wrong or I am thick but if you lock the focus on the eyes then recompose surely the focus wont be on the eyes any more? :shrug:
 
markw08 said:
I think it was probably about using the focus lock when shutter is half pressed...

For example for a portrait you would put your focus point on the eyes, half press the shutter to lock the focus then move the compostion whilst still holding shutter then fully press to take the shot...

You can as you say move the focus point around especially for static portraits...

:thumbs:
Click to expand...

thats rings a bell about half pressing, wasnt suite sure of the point.

if i set the photo and use auto focus, why would i only press half way and then reset myself?
 
Donki said:
Either I am picking you up wrong or I am thick but if you lock the focus on the eyes then recompose surely the focus wont be on the eyes any more? :shrug:
Click to expand...

It will still be focused as long as you or the model do not move backwards, you are merely panning the camera a short distance so focus will still be sharp.
 
Focus-recompose. Using just one focus point, it's the only way to be sure exactly where the focus point actually is.

Select one focus point (usually the centre, it's more sensitive) and position it over the area you want sharp. Half-press the shutter release and hold it, and the focus is locked. Recompose as you like, the press the release fully.

It's sometimes easier to do this by assigning AF to another button, such as the * button on Canons, but it's very easy either way.

Word of warning with portraits - it's one of the few subjects where you have to be extra careful with this technqiue because the depth of field is very shallow when you're shooting close with a low f/number - like 3-4cms or less at maybe f/1.8-ish.

With focus-recompose, you obviously have to move the camera after locking the focus. It's only a tiny amount, but it often means a shift in effective distance of maybe 1-2cm which can be critical. Switching from the centre focus point to one that is nearer the subject's eyes reduces this movement.

The other thing is that there's always a slight delay between focusing and shooting. It can be quite a long time if you hold the focus while waiting for the right expression. In that time it is very common for the subject to move slightly, and for the photographer too. You perhaps won't notice as couple of cms of movement until you look at the shots and see that they're out.

The answer here is to check and re-set the focus repeatedly. I sometimes do it more than once a second. It's easier when you're using a focus point close to the subject's eyes.
 
CGeezer said:
It will still be focused as long as you or the model do not move backwards, you are merely panning the camera a short distance so focus will still be sharp.
Click to expand...

I see, if you were using quite a large aperature would it not be difficult to nail it? I mostly use the focusing points when doing the few potraits I attemp but mite give this technique a go. :)
 
HoppyUK said:
Focus-recompose. Using just one focus point, it's the only way to be sure exactly where the focus point actually is.

Select one focus point (usually the centre, it's more sensitive) and position it over the area you want sharp. Half-press the shutter release and hold it, and the focus is locked. Recompose as you like, the press the release fully.

It's sometimes easier to do this by assigning AF to another button, such as the * button on Canons, but it's very easy either way.

Word of warning with portraits - it's one of the few subjects where you have to be extra careful with this technqiue because the depth of field is very shallow when you're shooting close with a low f/number - like 3-4cms or less at maybe f/1.8-ish.

With focus-recompose, you obviously have to move the camera after locking the focus. It's only a tiny amount, but it often means a shift in effective distance of maybe 1-2cm which can be critical. Switching from the centre focus point to one that is nearer the subject's eyes reduces this movement.

The other thing is that there's always a slight delay between focusing and shooting. It can be quite a long time if you hold the focus while waiting for the right expression. In that time it is very common for the subject to move slightly, and for the photographer too. You perhaps won't notice as couple of cms of movement until you look at the shots and see that they're out.

The answer here is to check and re-set the focus repeatedly. I sometimes do it more than once a second. It's easier when you're using a focus point close to the subject's eyes.
Click to expand...

Thats answered if for me then thanks Hoppy.
 
The theoretical problem with focus-recompose is that when you focus on an object say 2 metres away you have focused on a flat plane 2M away that is parralel to the film or sensor in the camera and recomposing by tilting or swinging the camera will shift this plane and cause focus error.

in practice the technique works well at normal apertures but using large apertures very close reduces DOF to just mm and as everyone says problems can result, so using closest focus point and minimal recompose is best.

The ultimate answer, of course is if your images are sharp you're doing ok.
 
also look up back button focus for your make/model. its perfect for these kind of situations where you can decouple the focus+exposure function from the one button into two seperate operations.
 
Just to be controversial, I really don't like focus and recompose. I don't know how people can do it and maintain a sharp photo at any f/number lower than f/4, because I sure can't manage it!
 
trencheel303 said:
Just to be controversial, I really don't like focus and recompose. I don't know how people can do it and maintain a sharp photo at any f/number lower than f/4, because I sure can't manage it!
Click to expand...

Yes, it ain't perfect but it's incredibly quick on a shot to shot basis and sometimes absolute focus is far from othe first priority....Robert Capa...Bill Brandt...

http://www.slideshare.net/peiman/50-most-notable-photos-of-all-time

Check out the slideshow...........focus?
 
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