Beginner Back button and auto focus

crundi

crundi

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Hi.
I've got myself a Canon 700d with a 50mm prime. I shoot RAW and usually in Manual mode. I've recently configured my camera with back button focus and was wondering what mode my auto focus should be set to... One Shot or Ai Servo?

I've challenged myself to get some decent shots of my 2 year old daughter (read constantly moving target) but the results are hit and miss when it comes to sharpness.

Can I switch between focus modes faster with back button focus?
 
crundi said:
Hi.
I've got myself a Canon 700d with a 50mm prime. I shoot RAW and usually in Manual mode. I've recently configured my camera with back button focus and was wondering what mode my auto focus should be set to... One Shot or Ai Servo?

I've challenged myself to get some decent shots of my 2 year old daughter (read constantly moving target) but the results are hit and miss when it comes to sharpness.

Can I switch between focus modes faster with back button focus?
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There's no need to switch between focus modes, you're making life difficult for yourself. If there's a chance something will move BBF and AI servo is fine, if it's static, you can use that and just release the AF when you've got focus, or you can switch to one shot.
 
Thanks, I understand that back button focus quickly pressed locks focus for that plane. But with Ai Servo set am I right in thinking I can hold back button to start tracking and press shutter whilst being held down?
 
BBF works well with A1 Servo- but you have to wait until focus is caught I dont know if the 700d give a continuous indication that it has focus.
 
Listen to Phil. Set AI Servo. Press back button and release for single point focus. Holds for continuous refocusing on moving stuff.
AI Focus is crap, avoid. All it does is tries to automatically switch between single and servo and it's not very good at it.

I find you often don't get focus confirmation but no biggie
 
Thanks fellas, I'll give it a whirl. It probably doesn't help that I'm working with a shallow depth of field (f1.8). She just has to sway and my focus has gone.
 
AI servo mode is predicting where the subject is going to be in a moments time when the shutter is open and focusing on that spot rather than focusing on where the subject is right now. With that in mind, you do want to be using one shot AF with a static subject. You will also get some out of focus shots using AI servo on moving subjects because they aren't always moving in a predictable way. It's best to take bursts of 3-4 shots at a time.
 
Paul Griffin said:
AI servo mode is predicting where the subject is going to be in a moments time when the shutter is open and focusing on that spot rather than focusing on where the subject is right now. With that in mind, you do want to be using one shot AF with a static subject. You will also get some out of focus shots using AI servo on moving subjects because they aren't always moving in a predictable way. It's best to take bursts of 3-4 shots at a time.
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I just looked this up and whilst my advice to use one shot AF for static subjects and AI servo for moving subjects was basically good, my reasoning was a little off. See the explanation from Canon's Chuck Westfall over at Canon Rumors. http://www.canonrumors.com/forum/index.php?topic=20182.0
 
crundi said:
Thanks, I understand that back button focus quickly pressed locks focus for that plane. But with Ai Servo set am I right in thinking I can hold back button to start tracking and press shutter whilst being held down?
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Yes
 
If you are using back button focus then I cannot see why you would choose anything but AI servo (AF-C on Nikon).

Using a mode that tries to predict is just going to take time that you probably don't want to waste.

This may make it clearer for anyone still thinking of using BBF and a predictive mode (AI Focus etc) or who is currently using a predictive mode but wants to try BBF.

View: https://m.youtube.com/watch?v=8PN9R0D3pF0


Dave.
 
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Dave Semmens said:
If you are using back button focus then I cannot see why you would choose anything but AI servo (AF-C on Nikon).

Using a mode that tries to predict is just going to take time that you probably don't want to waste.

This may make it clearer for anyone still thinking of using BBF and a predictive mode (AI Focus etc) or who is currently using a predictive mode but wants to try BBF.

View: https://m.youtube.com/watch?v=8PN9R0D3pF0


Dave.
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The reason I use ai focus is because it is faster to let the camera choose what to use than it is for me to switch back and forth between one shot and ia servo.
 
shaylou said:
The reason I use ai focus is because it is faster to let the camera choose what to use than it is for me to switch back and forth between one shot and ia servo.
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Have you tried back button focussing? (Not sure if all cameras support it but I think most recent DSLRs will)

I choose between single and servo (AF-C on my Nikon) by just pressing or releasing the button. I spent a fortune on a lens that will focus very, very quickly and the last thing I want is to leave it up to the camera to try and decide what I want as a bird takes flight from its perch. I want to control that.

Dave.
 
Dave Semmens said:
Have you tried back button focussing? (Not sure if all cameras support it but I think most recent DSLRs will)

I choose between single and servo (AF-C on my Nikon) by just pressing or releasing the button. I spent a fortune on a lens that will focus very, very quickly and the last thing I want is to leave it up to the camera to try and decide what I want as a bird takes flight from its perch. I want to control that.

Dave.
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Yes I have bbf set up on both my 5d's. I can see how bird taking off could be a problem but it seems like shooting with it on ai servo on a stationary subject is problematic as well. I mean that was not what it was intended for. I use ai focus as a general setting. When I shoot moving subjects I use ai servo.
 
shaylou said:
So if you give it a second it should work fine correct?
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But the point of the mode being that it'll automatically switch when needed? And if it doesn't switch 'instantly' it misses it's point.

If you're shooting a static subject that then decides to move, the camera will take a while to catch up, that 'second or 2' could be a couple or 10 missed shots. Feel free to use it, I con only offer my opinion.
 
shaylou said:
Yes I have bbf set up on both my 5d's. I can see how bird taking off could be a problem but it seems like shooting with it on ai servo on a stationary subject is problematic as well. I mean that was not what it was intended for. I use ai focus as a general setting. When I shoot moving subjects I use ai servo.
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There's definitely a risk with AI Servo and static subjects, where it 'can' predict movement and deliver OoF shots (though it's rare, it's why I mentioned sometimes using One Shot).

So if you are shooting a static subject, One Shot is faster than AI Focus (it's not trying to do anything smarter than achieving focus). I have to say though, I've never really tried it, because when I started shooting AF, I read all the available material and no-one recommended using it, every 'expert' said it was a PITA.
 
Phil V said:
But the point of the mode being that it'll automatically switch when needed? And if it doesn't switch 'instantly' it misses it's point.

If you're shooting a static subject that then decides to move, the camera will take a while to catch up, that 'second or 2' could be a couple or 10 missed shots. Feel free to use it, I con only offer my opinion.
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Thinking back I can see where it messed me up pretty good. I was at the floating village in Cambodia and had the opportunity of a lifetime shots. I got a lot of good shots but had a couple that were soft for no explainable reason. They were the kind of shots that you would do anything to get a do over on. But honestly, I really have not had any other times where it effected me. I am more conscious of it now that we have talked about it. (I shot today). I will keep it in mind a lot more now. Thanks.
 
Still on the subject of focus, I heard someone say that focus achieved through LiveView was consistently sharper over using the viewfinder. (I'm talking auto focus here, not zooming in and setting focus manually).
 
crundi said:
Still on the subject of focus, I heard someone say that focus achieved through LiveView was consistently sharper over using the viewfinder. (I'm talking auto focus here, not zooming in and setting focus manually).
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Not really, more of a theory, but can be true.

Normal AF works to a simulated focal plane and needs to be correctly calibrated between camera and lens. If it's not, AF will be out, whereas live view reads the actual focal plane (the sensor) so can't be wrong on that aspect.
 
HoppyUK said:
Not really, more of a theory, but can be true.

Normal AF works to a simulated focal plane and needs to be correctly calibrated between camera and lens. If it's not, AF will be out, whereas live view reads the actual focal plane (the sensor) so can't be wrong on that aspect.
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So would this be a good way of testing to see if calibration was needed? If I understand this correctly, you could manually focus though the view finder and do the same in live view and if the view finder focus was off and live view was correct it would mean that calibration was needed. Is that correct?
 
shaylou said:
So would this be a good way of testing to see if calibration was needed? If I understand this correctly, you could manually focus though the view finder and do the same in live view and if the view finder focus was off and live view was correct it would mean that calibration was needed. Is that correct?
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It's one way, but not a very good way.

The key to good AF is the target. Something flat and square to the camera, with zero possibility of the camera picking up on the wrong thing, and shot at a sensible distance. Like this cereal box, with the AF point somewhere around the 'ta'. AF on that, then see on the rule where the plane of actual focus lies.

 
shaylou said:
So would this be a good way of testing to see if calibration was needed? If I understand this correctly, you could manually focus though the view finder and do the same in live view and if the view finder focus was off and live view was correct it would mean that calibration was needed. Is that correct?
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Do you mean autofocus?
 
Paul Griffin said:
Do you mean autofocus?
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If my understanding is correct it wouldn't matter if it was in autofocus or manual focus. If there was a focus problem that was caused by a out of calibrated body/lens it could be found buy focusing in live view manually. That is more of a question than a statement. If my understanding of Mr Hoppy's post is correct I think this is how it should be.
 
shaylou said:
If my understanding is correct it wouldn't matter if it was in autofocus or manual focus. If there was a focus problem that was caused by a out of calibrated body/lens it could be found buy focusing in live view manually. That is more of a question than a statement. If my understanding of Mr Hoppy's post is correct I think this is how it should be.
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I took you to mean auto-focus, but the same kind of answer applies to manual focusing through the viewfinder. In that situation, you are focusing on another simulated focal plane - the surface of the viewfinder screen, just above the mirror.
 
Phil V said:
There's definitely a risk with AI Servo and static subjects, where it 'can' predict movement and deliver OoF shots (though it's rare, it's why I mentioned sometimes using One Shot).

So if you are shooting a static subject, One Shot is faster than AI Focus (it's not trying to do anything smarter than achieving focus). I have to say though, I've never really tried it, because when I started shooting AF, I read all the available material and no-one recommended using it, every 'expert' said it was a PITA.
Click to expand...

Sense this conversation I have been paying very close attention to how the focusing system performs and how long it takes to switch from a stationary target to a moving target or AI focus to AI servo. The camera does this very fast. It seems that there is a split second delay and I see y'all's point but if I am doing general shooting that spit second delay is way faster than manually switching servo modes no matter how you have it set up I'm pretty sure that was canons intension. I see why canon made this mode. If I were shooting birds in flight and waiting for them to take off I would definitely use AI servo but if the delay is the only point in not using it I don't see where it would matter in a lot of cases.
I was trying to shoot some bumble bees in flight the other day (wow that's hard) and I switch to AI servo and it did help. My point is, in my opinion they both are useful. I'm glad y'all pointed out the downfalls because that will help me choose the very best servo mode for the job. So thanks for that.
 
landwomble said:
Listen to Phil. Set AI Servo. Press back button and release for single point focus. Holds for continuous refocusing on moving stuff.
AI Focus is crap, avoid. All it does is tries to automatically switch between single and servo and it's not very good at it.

I find you often don't get focus confirmation but no biggie
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Agree. Half the time AI focus chooses the background, or a flight of wassailing unicorns, anything but the target.
 
One thing I've discovered is that single shot tries harder to grab focus in low light.

I'm also micro adjusting in Magic Lantern now via Dot Tune method...!
 
crundi said:
Still on the subject of focus, I heard someone say that focus achieved through LiveView was consistently sharper over using the viewfinder. (I'm talking auto focus here, not zooming in and setting focus manually).
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That's a complete myth. live View focuses by contrast. It doesn't employ all the focus points. If you're using live view then you are not using the cameras AF to its full potential.
 
shaylou said:
Sense this conversation I have been paying very close attention to how the focusing system performs and how long it takes to switch from a stationary target to a moving target or AI focus to AI servo. The camera does this very fast. It seems that there is a split second delay and I see y'all's point but if I am doing general shooting that spit second delay is way faster than manually switching servo modes no matter how you have it set up I'm pretty sure that was canons intension. I see why canon made this mode. If I were shooting birds in flight and waiting for them to take off I would definitely use AI servo but if the delay is the only point in not using it I don't see where it would matter in a lot of cases.
I was trying to shoot some bumble bees in flight the other day (wow that's hard) and I switch to AI servo and it did help. My point is, in my opinion they both are useful. I'm glad y'all pointed out the downfalls because that will help me choose the very best servo mode for the job. So thanks for that.
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That's a bit of a misunderstanding though Shayne, the advice is that we change focus system by situation, we don't wait for something to move then change it.

If it works for you then great, but I don't trust it, and that split second is too much for me.
 
i think the difference is that phil is talking about people going out with a specific intention - right today i'm shooting puffins/motorsport/whatever so i need AI servo - whereas shayne is talking about people bimbling about and seeing what pops up oh theres a bumble bee, theres a flower, theres a butterlfy , oooh prettty tree... so in the former selecting which focus mode you need is definitely the way forward, but in the latter AI focus is the only practical option
 
big soft moose said:
i think the difference is that phil is talking about people going out with a specific intention - right today i'm shooting puffins/motorsport/whatever so i need AI servo - whereas shayne is talking about people bimbling about and seeing what pops up oh theres a bumble bee, theres a flower, theres a butterlfy , oooh prettty tree... so in the former selecting which focus mode you need is definitely the way forward, but in the latter AI focus is the only practical option
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Must admit, I've never knowingly bimbled ;)
 
big soft moose said:
i think the difference is that phil is talking about people going out with a specific intention - right today i'm shooting puffins/motorsport/whatever so i need AI servo - whereas shayne is talking about people bimbling about and seeing what pops up oh theres a bumble bee, theres a flower, theres a butterlfy , oooh prettty tree... so in the former selecting which focus mode you need is definitely the way forward, but in the latter AI focus is the only practical option
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I still stand by saying AI Focus has no use.
If it's moving, you want AI Servo. If it's static, AI Servo will still nail focus nicely. If you're going to pick any mode to leave it in, use BBF and leave it in AI Servo - tap for one shot, press and hold for servo. Job done.

If it's very, very, very dark then oneshot with center point focus is marginally more sensitive on Canon.

AI Focus just adds a not very consistent other variable and will lower your success rate with no gain. I'd recommend you ignore it.
 
back on the original topic i don't get on with BBF, Ive tried it but i keep forgetting its there and half pressing the shutter button then wondering why nothing's focusing. That said I leave the camera in AI servo most of the time anyway, unless i'm doing a wedding where it goes in one shot.

AI focus was a good idea in theory, (like inteligent 4 wheel drive) if onlyu either worked as the designers envisaged
 
big soft moose said:
back on the original topic i don't get on with BBF, Ive tried it but i keep forgetting its there and half pressing the shutter button then wondering why nothing's focusing. /QUOTE]

You're not using your camera enough. Memory muscle will soon kick in and it'll be second nature in no time. It'll become an extension of your arm and you won't even have to think about it.
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