Back button focusing

[nescafe37]

Does anyone here use there back button for focusing? If so does it really make any difference?

[The Phantom]

Yes I use it - after seeing a number of top aviation photographers recommended it. It takes some getting used to when you first start doing it, but once you get used to it, it becomes second nature. What i read - and found myself - is that for some reason you get more keepers; more sharp images.

Also handy for where you want to focus on a subject and then move it off-centre before taking the shot.

[deerhunter]

Yes, wouldn't be without it, use it all the time

[Andy_99]

Just started experimenting with it as well

[daggerfan]

I would echo The Phantom's views about getting more keepers using back button focusing. I started using it about a year ago when I read most top sports photographers use it. Having had my fair share of dismal picture failures beforehand, I can certainly say back button focusing has worked wonders for my hit rate now!

[Velvet Glove]

Long time user of back-button; second nature to focus on what matters & 'then' compose the shot.

[Wallace]

It takes a bit of getting used to and would not go back

[lrv890]

I believe the reason for the higher keeper rate is that the auto focus doesn't stop , which it can do when you take your finger off the shutter button between shots . When you then refocus the camera / lens is playing catchup

[Dave Smith]

What is this back button?

[morticiaskeeper]

I know the back button, I just don't understand the concept of autofocus!

My manual focus 600mm prime cost me a fiver, and the thumb that focuses it never gets confused.

[Trenchard]

What is this back button?

There are some good articles and tutorials on the web, just Google back button focus - I've already read up and set my camera up ready to try next time I go out

[Cornish-guy]

An argument against and for shutter button focusing could be - when you are following just one plane in single shot mode, and at the same time keeping your eye on the exposure meter in manual exposure so that at the time of the exposure you are able to adjust as you need, with BBF the focus is separate from the exposure so you could be put out with a under/over exposed shot.

C.

[The Phantom]

An argument against and for shutter button focusing could be - when you are following just one plane in single shot mode, and at the same time keeping your eye on the exposure meter in manual exposure so that at the time of the exposure you are able to adjust as you need, with BBF the focus is separate from the exposure so you could be put out with a under/over exposed shot.

C.

That is some complicated way of taking a photograph! Never heard of anyone taking photos like that before.

[Viper28]

The back focus button (by default - it can be reconfigured) simply disassociates the autofocus function from the metering / shutter release. You use the button to activate AF and continually track a subject in continuous or AI-Servo modes. Pressing the shutter release then meters, closes down the lens and takes the shot. The idea is that when you stop shooting and release the shutter AF continues, so any follow on shots do not have to first activate AF etc. If you shoot in machine gun mode, ie shoot continuously from the moment you see the object with no break, the back focus button has no advantage.

[Wallace]

Go over onto Youtube and enter Back Button focus and you see what is means

[Cornish-guy]

An argument against and for shutter button focusing could be - when you are following just one plane in single shot mode, and at the same time keeping your eye on the exposure meter in manual exposure so that at the time of the exposure you are able to adjust as you need, with BBF the focus is separate from the exposure so you could be put out with a under/over exposed shot.

C.

That is some complicated way of taking a photograph! Never heard of anyone taking photos like that before.

Basically means that the lighting conditions can and do change if you are following a plane - as the plane gets closer and takes up more of the view, the exposure can drop requiring adjustment if you are using manual (M) exposure rather than the semi auto controls.
If you are using the BBF tech for focus you could end up with an under exposed shot.

C.

[Viper28]

An argument against and for shutter button focusing could be - when you are following just one plane in single shot mode, and at the same time keeping your eye on the exposure meter in manual exposure so that at the time of the exposure you are able to adjust as you need, with BBF the focus is separate from the exposure so you could be put out with a under/over exposed shot.

C.

That is some complicated way of taking a photograph! Never heard of anyone taking photos like that before.

Basically means that the lighting conditions can and do change if you are following a plane - as the plane gets closer and takes up more of the view, the exposure can drop requiring adjustment if you are using manual (M) exposure rather than the semi auto controls.
If you are using the BBF tech for focus you could end up with an under exposed shot.

C.

No the BFB only activates the AF not metering, it's in the name

[Cornish-guy]

Yep the BBF does only govern focusing and as long as the lighting conditions don't change to much, when you are using manual exposure control requiring shut speed adjustment/ AP adjustment along with ISO adjustment.
This is different if you are in any of the auto settings as its taken care of exposure automatically.

A scenario of this mite be - you have taken a photo of a static plane in manual exp, then you want to take a pic of something flying - so you use your BBF and follow the plane without doing anything else then when you examine the shot - it is underexposed because you did not see the exposure meter telling you about being under, as it would if you were using the shutter button for both focus and exposure control.

As I explained this is not an issue if the camera is adjusting exposure itself.

C.

[Sparts99]

I recently looked into this.

http://www.colesclassroom.com/back-butt ... 185bc74a22

as I found my canon 50/1.4 on my 7D was very slow responding in low light in any focus mode. Most of my photography is gigs and events so subjects are usually moving about a fair amount, I use servo rather than one shot usually but was losing a few good shots as the lens was responding so slowly. I tried the back focus button on my last shoot and got a higher success rate for sharp pics as the lens was always tracking the selected AF point. Holding the shutter button halfway forces the focus to track too but locks the exposure, with light levels fluctuating as wildly as they do manual exposure isn't really an option, usually aperture priority and the exposure compensated to allow for front or back lighting, framing, and lens characteristics. So for me this function is really useful.

I usually take some shots in manual if I'm after a specific effect, but I don't think the exposure meter in the viewfinder stops working when using the back focus button (I don't pay attention to it) so don't really understand Cornish Guy's comment 'it is underexposed because you did not see the exposure meter telling you about being under'. In any event if you go from shooting a static plane to a flying you'll always need to open up to some degree to prevent getting a silhouette or underexposed shot whther in manul or using an automatic mode.

[Sparts99]

I meant to add, 'back focus button' is a slightly ambiguous term. In this case it means the focus is controlled by a button on the back of the camera. 'Back focus' also refers to the focus on the image sensor. TV camera zoom lenses with zoom ratios up to nearly 100x have an adjustment for this, the lens is focussed on a distant subject at the tele end, the zoomed to wide, and the back focus adjusted to get the sharpest picture, zoomed to tele and repeated until no adjustment is required at each end, then in theory the focus will track right through the zoom range. Each lens and camera will be very slightly mechanically individual and affected by temperature so this is checked before every shoot. At least if the camerman knows what he's about. This is also relevant to DSLRs but is called micro adjustment but as the zoom ratios on pro stills lenses are much lower, 3-4x the tolerances can be kept that much tighter in manufacture.