Back Button Focusing - an unexpected snag

[davidedric]

Hi,

A couple of weeks ago I started a thread asking for guidance on back button focusing. I got lots of feedback, set it up on my 600d, had a bit of practice, and decided to give it a go on my recent holiday.

My way of working for wildlife is to focus on the appropriate point, re-compose, wait for the position that I want, and shoot.

The snag I realised is that image stabilisation only lasts for a second or two after the button press and release which is a big problem when hand holding a long zoom. I only realised what was going on when I missed the slight noise of the mechanism, fortunately early on in the trip.

So I reverted to the half-press which maintains the IS so long as it is held. I didn't want to experiment further.

Any comments gratefully received.

Dave

[Mark von Kanel]

Dave if you half press the shutter the VR stays active

sorry to make it more clear, once youve achieved focus and the VR stops if you then half depress the shutter button the VR spins back up, so you need to half press a second or so before you take the shot. equally if you keep the shutter button half press after achiving focus the vr will stay active.

oops thats how it works for nikon, not sure about canon....

[davidedric]

sorry to make it more clear, once youve achieved focus and the VR stops if you then half depress the shutter button the VR spins back up, so you need to half press a second or so before you take the shot. equally if you keep the shutter button half press after achiving focus the vr will stay active.

Thanks, Mark. The problem is that I don't know a second in advance that I am going to take the shot! Elephants just aren't that predictable.

Dave

[Mark von Kanel]

Then its horses for courses if its not going to spin up in time with a half press with bbf then it wont with half press either.

[davidedric]

Not exactly. With bbf you press and release (at least on my camera). With the half press you keep holding, so the IS keeps spinning.

[dje]

Dave if I recall correctly, I have the same lenses as you. i have only tried bbf on the Sigma 17-70 and as far as I know that works fine (but I should check that). I haven't tried in on the Tamron 70-300. The IS on this lens is a bit strange and I have never figured out exactly how it operates so I can see there could be a problem. Must have a play.

Dave

[Glenn NK]

Superfluous post. Deleted

[Mark von Kanel]

as i understand it Dave, and im by no means an expert as ive only just started using the method myself is that by using BBF you can use the constant focus mode all the time but have the benefit of being able to re compose by releasing the BFB if you want to keep the is going just depress the shutter button half at the same time and keep it depressed until you shoot

If you use that method you get the benefit of both constant focus and single focus modes at the same time, if your subject is moving then keep you bbf down and shoot, if its stationary bbf down - release - recompose - shoot. if you let go of the bbf and want to keep IS going then keep shutter half depressed.

[ajohnw]

I've tried it on a D7000. The camera only focuses when the back button is pressed. I saw video extolling it's virtues if the subject moves. As I see it the main advantage is to lock focus. If the camera needs to continuously focus then the back button has to be pressed. Suppose in real terms it saves changing focus modes but if focus can be locked some other way I can't really see the point.

John
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[Mark von Kanel]

Suppose in real terms it saves changing focus modes but if focus can be locked some other way I can't really see the point.

I think that is the only benefit John but if it saves you taking your eye from the viewfinder to change modes then its worth it i suppose.

[krispix]

Hi Dave,

It's a bit retro, I know. But, how about manual focusing? That's the way we did it before AF & IS and all the other fancy stuff that modern cameras do for you. I've got pin sharp pictures of lions and cheetahs from 40 years ago, and they both move a lot quicker than elephants. Just saying.

[Cliff Roamer]

I've tried it on a D7000. The camera only focuses when the back button is pressed. I saw video extolling it's virtues if the subject moves. As I see it the main advantage is to lock focus. If the camera needs to continuously focus then the back button has to be pressed. Suppose in real terms it saves changing focus modes but if focus can be locked some other way I can't really see the point.

John
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I don't know how Dave's Canon and lens works but with my Nikon you set up bbf so you only press it once and it locks and the VR doesn't kick in again, or at least I don't hear it, (keep pressed for continuous focus) and if you also set the shutter release so the exposure locks when pressed halfway you can then expose and recompose with the shutter release but the auto focus doesn't start again, some people might find this method awkward or unnecessary but I like the complete separation and control it gives over auto focus and exposure, will it help me take better pictures, no comment

[DanK]

Dave,

This may differ among models even within the canon line, but on my canon body, the IS behavior is identical regardless of which button you assign to AF. Changing the button assignment only changes which button you use to trigger it. In single shot AF, the IS stays on as long as you have the back button depressed or the shutter half depressed, depending on which button you use, and it stays on for only a short time after you release the button. I use AI servo so rarely that I haven't checked those, but I would guess it is the same deal--the same behavior regardless of the button.

My practice is simple. Most of the time, I leave AF on the back button. Now that I am used to it, I find it convenient, and it frees me from worrying about turning on the AF when I don't want to. E.g., you can forget about focus-lock-recompose; there is no need to lock. You can manually refocus, if your lenses have full-time manual focusing, and not have the shutter refocus. When it is inconvenient to have it on the back button, or if I am going to hand the camera to someone else, I put it back on the front button.

Dan

[William W]

A couple of weeks ago I started a thread asking for guidance on back button focusing . . . and decided to give it a go on my recent holiday. My way of working for wildlife is to focus on the appropriate point, re-compose, wait for the position that I want, and shoot.

I haven’t read you previous thread. I am ignorant of what was advised.

For clarity this is your procedure as I understand what you have written:
1. focused using the back button
2. [assumed used centre point only AF] therefore recompose framing
3. wait for subject expression etc
4. shoot

I see no relevant issue with that procedure.

***

The snag I realised is that image stabilisation only lasts for a second or two after the button press and release [assumed this is the back button focus press and release which activates the IS] which is a big problem when hand holding a long zoom. I only realised what was going on when I missed the slight noise of the mechanism, fortunately early on in the trip.

That is correct.

When Back Button Focus is assigned, then Depress Back Button will also activate IS.

IS, once activated, stays active for a couple of seconds beyond the depression time of the button.

***

So I reverted to the half-press [Shutter Release Button for Focussing] which maintains the IS so long as it is held.

As I understand your problem, you reverted to assigning the 'Half Depress Shutter Release' for Auto Focus, simply to have the IS activated by 'Half Depress Shutter Release'. This is not necessary.

The reason it is not necessary is because,
When Back Button Focus is selected:

1. Image Stabilization Activation assignment is moved to Back Button
2. Image Stabilization Activation assignment is NOT REMOVED from ‘Half Depress Shutter Release’.


As I understand Canon AF Assignment / IS Assignment Functionality - that statement is correct for all EOS Series Cameras and EF and EF-S Series Lenses.

***

Please advise if I have not correctly understood you problem.

WW

[skilsaw]

Then its horses for courses if its not going to spin up in time with a half press with bbf then it wont with half press either.

Jargon and acronyms do nothing for reading comprehension by relatively inexperienced like me.
What is "...not going to spin up in time..."?
What is bbf?
What is VR? from a previous post.

[FootLoose]

BBF = Back Button Focus

VR = Nikon's Vibration Reduction; similar to Canon's IS = Image Stabilisation

[Glenn NK]

Superfluous post. Deleted.

[Mark von Kanel]

Jargon and acronyms do nothing for reading comprehension by relatively inexperienced like me.
What is "...not going to spin up in time..."?
What is bbf?
What is VR? from a previous post.

The acronyms have been covered and although im sympathetic David you are going to have to learn them, there simply isnt the time to type common technical terms in full every time. If theres something your not sure of just ask or google it.

The spin up bit was i believe explained in anther post on here and relates to the time it takes the gyro sensors to start up or spin up as thats what gyros normally do

other acronyms you may need.

OOC out of camera (non edited image)
OOF out of focus
DOF depth of field

theres a whole plethera of other related to individual camera makes youll get used to em

[dje]

Dave

I had a play with my Sigma 17-70 and Tamron 70-300 lenses on the 600D set up for bbf. I found that the IS seems to be actuated by either the back button or the shutter button (half activated). I'm assuming IS is activated when you can hear the whirring sound of the gyro sensors. (This is very quiet on the Sigma).

With the Sigma, when the back button or shutter button is released, the IS seems to stay on for quite a long time. However with the Tamron, it seems to shut down after a couple of seconds. The other thing about the Tamron is that the instruction leaflet indicates that after IS has been activated, it is not ready for use for about 1 sec.

As a result of this. it seems to me that to use the Tamron with bbf, you need to set your bbf and then half hold down the shutter button for at least a second before taking the shot.

But as I said in an earlier post, I'm not certain how the Tamron actually operates.

Dave

[davidedric]

Hi everyone,

Thanks for all the feedback and comments. Dave Ellis (who does indeed have exactly the same kit as me) describes things perfectly:

However with the Tamron, it seems to shut down after a couple of seconds. The other thing about the Tamron is that the instruction leaflet indicates that after IS has been activated, it is not ready for use for about 1 sec.

As a result of this. it seems to me that to use the Tamron with bbf, you need to set your bbf and then half hold down the shutter button for at least a second before taking the shot.

In other words, with this camera and lens, bbf will not do what I need it to: accurate focusing, image stabilisation and instant shooting when the moment is right.

Just for completeness, I had the autofocus set to AI Servo, and the appropriate customisation set. The intent being that a single press on the bb gives the correct focus, and a continuous press activates the servo mode should the animal move. The focussing worked just as it should.

The single issue was having the IS running when I needed to take the shot at no notice, and as Dave E has shown, this is not possible.

Thanks,

Dave