Focusing on subjects eyes

J

jimmy83

Suspended / Banned
Messages
2,154
Name
James
Edit My Images
Yes
Ive started to try and play about with my focus points abit now, and ive been using my middle focus point to focus on one of the eyes.

But as you can only select one or all point/s iam struggling to figure out how would I select both eyes in focus when iam only able to use one focus point if that makes sense.

I think my 40d has 9 points.
 
Use the centre AF point, focus on the nearest eye, lock it, and then recompose the image as you want it. Standard technique - centre AF point is more reliable.

If that's inconvenient or doesn't suit the situation/subject for some reason, which will not be that often, use the nearest AF point.
 
Ok thats, do you know how to lock the AF point?
 
To lock the focus point with most cameras you just half press the shutter release button, then fully press to take the pic.

So the sequence would be:
1. Focus on the point you want to be in focus
2. Half press and hold the shutter release button
3. Recompose
4. Fully press to take the pic.
 
Another way to do it, and this is what I have been using for several months now after discovering it, is what is known as back-button focussing. If you go into the menu on your camera, you will be able to change which button focusses, and remove that function from the shutter button to the AF-on button at the back of your camera.

That way you can focus on your subject and it doesn't matter if you let go of the shutter button.

A full guide can be found here http://www.rickykphotography.com/tutorials/camera/back-button-focusing/

The only issue I find with using this method to focus is that if I give my camera to a friend to take a shot with me in it, I have to change the function back in the menu to the more traditional set up!
 
Last edited:
Or another method is to change the focal point as highlighted in the camera to place it on the subject without moving the camera.

But focus and recompose works possibly quicker depending on your camera.
 
Is there a risk of the camera incorrectly calculating the exposure when recomposing?
 
PatrickO said:
To lock the focus point with most cameras you just half press the shutter release button, then fully press to take the pic.

So the sequence would be:
1. Focus on the point you want to be in focus
2. Half press and hold the shutter release button
3. Recompose
4. Fully press to take the pic.
Click to expand...

This is the method I use... Only ever use centre point for most of my work!
 
icstm said:
Most cameras allow you to only lock focus and not exposure.
Click to expand...
I don't think that's the case. You can do both. You certainly can on a 450D. If you use the back button focus method, you can use the shutter button to lock the exposure, or you can use the back button to lock the exposure and the shutter one to focus. There are other combinations as well, but not being by my camera at the moment, I cannot recall what these are.
 
Question - in automode, why does a camera sometimes choose 1 focal point and sometimes 3, 4, 5 + ?
 
damianmkv said:
Question - in automode, why does a camera sometimes choose 1 focal point and sometimes 3, 4, 5 + ?
Click to expand...

In auto, it will light up all AF points where the subject is within the zone of acceptable sharpess - could be one, or even most of them, eg flat surface.

It will (almost) always give priority to the nearest part.
 
When you have two subjects in your frame, ie two people as you are supposed to focus on the eyes if both people are level with each other and you use center point focus point. What do you focus on?
 
jimmy83 said:
When you have two subjects in your frame, ie two people as you are supposed to focus on the eyes if both people are level with each other and you use center point focus point. What do you focus on?
Click to expand...

An appropriate point that when you take into account the depth of field will give you the depth of focus you need. You need to judge where that point is and what aperture you will need as it will vary according to how the subjects are arranged.


BTW, have you found the menu option that lets you set the focus pount using the thumb-joystick? It's very effective on the 40D and once you get it set you'll wonder how you managed without it.
 
jimmy83 said:
When you have two subjects in your frame, ie two people as you are supposed to focus on the eyes if both people are level with each other and you use center point focus point. What do you focus on?
Click to expand...

Lock focus on the eyes (or faces will be good enough in that situation) then recompose - as per post #2. This is a very reliable technique and works well in a wide range of situations.

You need to understand depth of field, which you can calculate here http://www.dofmaster.com/dofjs.html For example, if you had two people standing one behind the other and you wanted them both sharp, you need to enure you have sufficient DoF and if that is marginal then focus on a mid-point between the two in order to maximise it.

Mostly you don't have to worry about DoF for focusing too much, as there will be plenty of it if you shoot at normal distances at f/5.6 or higher. DoF reduces with image size (ie when you move closer, or use a longer lens) and with lower f/numbers. Play with that DoFmaster calculator and see how it changes.

Edity: crossed post with Alastair
 
Last edited:
Just to add to my comment and Richard's.. as well as an understanding of depth of field, an understanding of trigonometry (the old 3-4-5 triangle type of thing) is also needed when using focus-recompose and shallow a shallow depth of field.

The plane of focus is just that, a flat plane parallel to your sensor. It is *not* an arc of equal distance from your camera.

So if you're using a shallow depth of field and shooting mutiple subjects, you might focus on one eye at an angle to the direction you will eventually recompose to shoot. But you want the point you focus at to be as close to the direction you will eventually be shooting at. Otherwise when you recompose, trigonometry rears it's head and your focus point is now beyond your subject.
 
Alastair said:
Just to add to my comment and Richard's.. as well as an understanding of depth of field, an understanding of trigonometry (the old 3-4-5 triangle type of thing) is also needed when using focus-recompose and shallow a shallow depth of field.

The plane of focus is just that, a flat plane parallel to your sensor. It is *not* an arc of equal distance from your camera.

So if you're using a shallow depth of field and shooting mutiple subjects, you might focus on one eye at an angle to the direction you will eventually recompose to shoot. But you want the point you focus at to be as close to the direction you will eventually be shooting at. Otherwise when you recompose, trigonometry rears it's head and your focus point is now beyond your subject.
Click to expand...

I think this problem is exaggerated, and doesn't often happen in practise. It only occurs in rare circumstances when you are very close, like a couple of feet away, shooting at a very low f/number like f/2.8 or less, and the subject is a long way towards the edges of the frame.

And a much more likely cause of problems in that situation is either subject movement or the photogrtapher moving fractionally after focusing. It was discussed at length on this thread, and I posted a couple of example pictures http://www.talkphotography.co.uk/forums/showthread.php?t=359612
 
HoppyUK said:
I think this problem is exaggerated, and doesn't often happen in practise. It only occurs in rare circumstances when you are very close, like a couple of feet away, shooting at a very low f/number like f/2.8 or less, and the subject is a long way towards the edges of the frame.

And a much more likely cause of problems in that situation is either subject movement or the photogrtapher moving fractionally after focusing. It was discussed at length on this thread, and I posted a couple of example pictures http://www.talkphotography.co.uk/forums/showthread.php?t=359612
Click to expand...

I think it's probably more common that you think Richard. There's a temptation to shoot portraits with the nifty-fifty and get in close with the aperture opened up. Or choose a wider lens for a small group portrait rather than move the camera back. I've seen more than a few portraits where the far eye was in focus rather than the near eye and wondered if this was in part a trig problem.

Anyway, my point is that both DOF and trig are something to be aware of.. because understanding both of these will help minimise the potential for problems and help understand the technical as well as aesthetic advantages of a longer focal length for portraits (even group portraits).
 
Use centre focus point and focus on the bridge of the nose. Works every time
 
I switched to back button focusing a while ago, also changing the shutter button to be the metering lock when half pressed. It doesn't take long to get used to it, and I can't see me going back to the defaults.
 
Goody13 said:
A full guide can be found here http://www.rickykphotography.com/tutorials/camera/back-button-focusing/
Click to expand...

Thanks, handy guide especially as I use a Canon 40d

Alastair said:
BTW, have you found the menu option that lets you set the focus pount using the thumb-joystick? It's very effective on the 40D and once you get it set you'll wonder how you managed without it.
Click to expand...

Iam just using the dial at the moment to switch focus points, although Iam hardly using it now as iam just keeping the focus point on the center point for the time being.

tms789 said:
Use centre focus point and focus on the bridge of the nose. Works every time
Click to expand...

Good tip thanks, but how would this work if you had say 2 or 3 people in view?

DH59 said:
I switched to back button focusing a while ago, also changing the shutter button to be the metering lock when half pressed. It doesn't take long to get used to it, and I can't see me going back to the defaults.
Click to expand...

Thanks I think iam happy at the moment with the standard way but may try it in future.
 
Alastair said:
I think it's probably more common that you think Richard. There's a temptation to shoot portraits with the nifty-fifty and get in close with the aperture opened up. Or choose a wider lens for a small group portrait rather than move the camera back. I've seen more than a few portraits where the far eye was in focus rather than the near eye and wondered if this was in part a trig problem.

Anyway, my point is that both DOF and trig are something to be aware of.. because understanding both of these will help minimise the potential for problems and help understand the technical as well as aesthetic advantages of a longer focal length for portraits (even group portraits).
Click to expand...

I found when I did some portraits of my step daughter a while ago with a nifty fifty wide open, I found on some (predominatly the shots where I got up close and personal!) that the distance between what was sharp and what was obviously out of focus was very little.
To overcome the problem I simply stopped the lens down which enabed me to get the shots on that occassion.
Reading Alastairs posting has got me wondering if the problem was trigonometry based....I don't wish to sound a little slow or dim, but would it be possible for someone to explain in simple terms how this trigonometry effects an image......
 
Last edited:
Asha said:
I found when I did some portraits of my step daughter a while ago with a nifty fifty wide open, I found on some (predominatly the shots where I got up close and personal!) that the distance between what was sharp and what was obviously out of focus was very little.
To overcome the problem I simply stopped the lens down which enabed me to get the shots on that occassion.
Reading Alastairs posting has got me wondering if the problem was trigonometry based....I don't wish to sound a little slow or dim, but would it be possible for someone to explain in simple terms how this trigonometry effects an image......
Click to expand...

Follow the link in post #18 for explanation and examples, and also check the links on that thread for the trig bit.
 
You must log in or register to reply here.
Back
Top