Beginner Focus and Recompose (For Multiple images?)

[bigtel]

Hi all,

When taking photos of a person I usually use spot focus (with the focus point in the centre), focus on the eyes with a half press of the shutter, recompose then take the shot.

If I then want to take another photo with the same composition I have to repeat the above method.

I know I can select the focus point on my camera to say the far right but just say that's not exactly where I want my subject etc.

Is there a way I can do the focus, recompose method and take multiple shots without having to go back and focus?

Thanks

 

[HoppyUK]

Yes, it's called 'back-button AF' and most people prefer it, mainly for the reason you've given. It simply means that the AF function is removed from the shutter release, and assigned exclusively to the AF button on the back. Most DSLRs allow this, in the custom function menus - see handbook.

 

[Paul Male]

Back button focus as said above.

 

[posiview]

Yes, it's called 'back-button AF' and most people prefer it, mainly for the reason you've given. It simply means that the AF function is removed from the shutter release, and assigned exclusively to the AF button on the back. Most DSLRs allow this, in the custom function menus - see handbook.

This was one the the best bits of advise I was ever given.

Cheers.

 

[bigtel]

Thanks all.

 

[Pookeyhead]

Hi all,

When taking photos of a person I usually use spot focus (with the focus point in the centre), focus on the eyes with a half press of the shutter, recompose then take the shot.

Well stop doing that You're shifting the plane of focus. Do this on a close up portrait with a wide aperture, and you're causing issues.

http://www.bobatkins.com/photography/technical/focus_recompose.html


Use a more suitable focus point - that's why there are many of them.

 

[HoppyUK]

Well stop doing that You're shifting the plane of focus. Do this on a close up portrait with a wide aperture, and you're causing issues.

http://www.bobatkins.com/photography/technical/focus_recompose.html


Use a more suitable focus point - that's why there are many of them.

Not necessarily, that's more of a theory than a practical concern except in some quite rare situations. For there to be a significant error in focus-recompose accuracy, you have to be a) very close, like under 3ft, b) be using a very low f/number like f/2 or below with very shallow depth-of-field, and c) the key factor, the focused point needs to be a long way off-centre a creating a big angular shift between focused and recomposed positions.

It's certainly a factor to bear in mind, and using an outer focus point is prudent, but the more common cause of focusing error in a situation like this is subject and/or camera movement between focusing a shooting moments. Even just normal breathing can be enough to throw it out by a cm or two.

 

[Pookeyhead]

Not necessarily, that's more of a theory than a practical concern except in some quite rare situations. For there to be a significant error in focus-recompose accuracy, you have to be a) very close, like under 3ft, b) be using a very low f/number like f/2 or below with very shallow depth-of-field, and c) the key factor, the focused point needs to be a long way off-centre a creating a big angular shift between focused and recomposed positions..

Like what you get when shooting a headshot, or head and shoulders shot with a wide aperture you mean... hardly rare.

There are enough practical examples with 100% crops showing the difference on the net for people to verify this without me posting them here.

All DSLRs have multiple AF points now... it's far better to just compose the shot and then select the AF point you need. It's not exactly difficult.


The point you make about movement between focusing and actually taking will also be negated by using the correct AF point. In short, there's absolutely no good reason to focus and recompose that I can see... only disadvantages. It's just laziness that prevents people from doing it properly.

 

[HoppyUK]

Like what you get when shooting a headshot, or head and shoulders shot with a wide aperture you mean... hardly rare.

There are enough practical examples with 100% crops showing the difference on the net for people to verify this without me posting them here.

All DSLRs have multiple AF points now... it's far better to just compose the shot and then select the AF point you need. It's not exactly difficult.


The point you make about movement between focusing and actually taking will also be negated by using the correct AF point. In short, there's absolutely no good reason to focus and recompose that I can see... only disadvantages. It's just laziness that prevents people from doing it properly.

Just try it. Most of the examples I've seen of focus-recompose issues are seriously flawed and not representative. And if you do a test (as described a, b, c, above) then you'll find it only applies to a ridiculously close shooting distance and unlikely set of circumstances.

Not that I'm denying the theory exists, or that using outer AF points is not a good idea. But more to the point, the main cause of inaccurate focus in a portrait with very shallow depth of field, is subject and/or camera movement between focusing and shooting - and that applies to every shallow DoF portrait. It comes up a lot, and the common response is to trot out that focus-recompose theory when nine times out of ten it's not that at all.

 

[Pookeyhead]

Just try it.

I have. Which is why I no longer do it.

 

[HoppyUK]

I have. Which is why I no longer do it.

LOL. I got off on the wrong foot here. I'm not out to diss the focus-recompose error theory other than to say it only applies to a rare and fairly extreme set of circumstances. The Bob Atkins article you linked is a fair summary.

What I'm really trying to say is that focusing errors are very common when depth of field gets down to a couple of cms. There can be various reasons for that, but by far the most common is unnoticed subject and/or camera movement and distance change between focusing and shooting. The solution therefore is to keep still, try to get your subject to stay still, focus carefully and keep checking and rechecking right up to the moment before shooting.

 

[Pookeyhead]

LOL. I got off on the wrong foot here. I'm not out to diss the focus-recompose error theory other than to say it only applies to a rare and fairly extreme set of circumstances. The Bob Atkins article you linked is a fair summary.

What I'm really trying to say is that focusing errors are very common when depth of field gets down to a couple of cms.

Which is why moving the camera even slightly after focusing, and before pressing the shutter is a really bad idea. Use a AF point that is where you need to focus and there's no delay or movement of the camera - and there's also no shift in plane of focus.

It's clearly best practice, so it should be something everyone just does IMO. I can't think of a single reason not to.

There can be various reasons for that, but by far the most common is unnoticed subject and/or camera movement and distance change between focusing and shooting.

Which is greatly reduced if you can just focus and shoot without needing to move the camera in between.

The solution therefore is to keep still, try to get your subject to stay still, focus carefully and keep checking and rechecking right up to the moment before shooting.

Of just use a AF point that's actually over the area you want sharp, and not have to bother getting your model's to "freeze" which makes them look awkward and contrived.

There's simply no reason not to... so I don't see what the problem is here. I mean... why are people so insistent on using the centre point?

 

[Phil V]

... I mean... why are people so insistent on using the centre point?

Because the internet is full of people telling us how the centre point is the best sensor (and because on lots of cameras out there it's actually true)

 

[HoppyUK]

Because the internet is full of people telling us how the centre point is the best sensor (and because on lots of cameras out there it's actually true)

And it's just easier - you always know where it is even when it's hard to see. Sometimes it is more reliable, and as accurate 99.999% of the time.

It's a subjective thing, each to their own, but I mostly end up using the centre point and recomposing.

And David, the point about very shallow DoF and the camera/subject moving between focusing and shooting, is much less to do with which AF point you use. It's much more about continually checking and re-checking focus, but if you prefer to do that with an outer AF point, then that's cool

 

[Pookeyhead]

And it's just easier - you always know where it is even when it's hard to see.

It lights up red... pretty hard to miss. Well.. it does on most cameras I've used.

Sometimes it is more reliable, and as accurate 99.999% of the time.

I tested them all with my D800s due to the fear of having the left AF point fault, and they all seem to be as reliable as each other. I can't comment on other cameras though, but I've never had an issue with my D600 or D610, or the D7000 I used to have, or indeed any other.

It's a subjective thing, each to their own, but I mostly end up using the centre point and recomposing.

I do to if it's a wide shot, or a full length portrait. With head and shoulders or head shots, I've missed focus too many times when using wide apertures by recomposing. I know it is that, because I don't any more since I stopped doing it. With close up portraits, the difference in focal plane will pretty much negate any perceived increase in accuracy you feel you may got from the centre point.

 

[HoppyUK]

<snip>
I do to if it's a wide shot, or a full length portrait. With head and shoulders or head shots, I've missed focus too many times when using wide apertures by recomposing. I know it is that, because I don't any more since I stopped doing it. With close up portraits, the difference in focal plane will pretty much negate any perceived increase in accuracy you feel you may got from the centre point.

If you are missing focus in the way you suggest, then you must be extremely close and have the focused point a very long way off-centre. Since that's just basic bad practise, I think it's probably unlikely and I would respectfully suggest that the focus-recompose method is not the main contributor to any problems. Focus-recompose technique also makes a slight difference, if you are pivoting the camera around say the tripod bush as opposed to the entrance pupil.

But I really don't want to argue about focus-recompose - I accept it can have an impact in rare circumstances. All I really wanted to say was that when shooting any 'live' subject with very shallow DoF, then you must keep checking and rechecking focus because there's a very good chance that either you or the subject will move imperceptively, but enough to throw the focus out.

 

[Pookeyhead]

If you are missing focus in the way you suggest, then you must be extremely close and have the focused point a very long way off-centre. Since that's just basic bad practise, I think it's probably unlikely and I would respectfully suggest that the focus-recompose method is not the main contributor to any problems.

Yes.. they were close. I've already said this is headshots etc. with very wide apertures. Focus on eye... recompose. Pretty standard stuff. I noticed a difference between recomposing and using a AF point already at where I needed (or very close to it). I would also respectfully suggest that I know how to focus a camera I always try to pivot around the focal node, so the adjusted focal plane still intersects the point focused upon, but with the camera to your eye, this is far from an exact science.

But I really don't want to argue about focus-recompose - I accept it can have an impact in rare circumstances. All I really wanted to say was that when shooting any 'live' subject with very shallow DoF, then you must keep checking and rechecking focus because there's a very good chance that either you or the subject will move imperceptively, but enough to throw the focus out.

It's hard to visually check focus visually with a DSLR.. unless you check after you've shot it... which is not always possible anyway, and even if it is, makes you look like an idiot if your working with other people around. I'd rather get it right first time, and not have to chimp in order to check something as fundamental as achieving sharp focus.

Anyway... Works for me. I've got 51 AF points... seems stupid using one of them for everything.