Back Button AF?

I use BBF with 1 shot all the time. It allows me to focus/recompose without fear fear of accidentally refocusing. Separating the fumctions has more than one benefit.

gonzogolf wrote in post #17813239
I use BBF with 1 shot all the time. It allows me to focus/recompose without fear fear of accidentally refocusing. Separating the fumctions has more than one benefit.

Same here!

I forced myself to switch to back-button AF about 6 months ago. I finally switched back a couple weeks ago. For me, it just seemed to add an unnecessary step to a simple process. If you are shooting sports or birds, then I can see the usefulness.

For portraits, weddings, and general event photography I didn't think it was helpful. In fact, I'm pretty sure it was the reason I missed focus on so many shots at a recent wedding. Almost every shot of a moving subject (ie. walking down aisle) was slightly OOF. That has never happened to me before. Perhaps I could have corrected the issue by using AI Servo, but I just don't see the real benefit in these situations. If I need to focus/recompose and am worried about a potentially significant change in lighting that would affect metering, I meter for the subject using the AE-lock and then recompose.

don1163 wrote in post #17813074
When I changed to back button focus the trouble I had was that I kept pressing the AEL button by mistake as it is close to the AF button...I now have both the AF button and the AEL button set to focus so it doesn't matter if I press the wrong one

In the old days, there was no AF ON button, and we used the * or "AE Lock" button.

Does the camera AF stationary objects as accurately when momentarily focusing in servo as it does in one-shot? The idea that BBF allows both one-shot and servo just by holding (or not) the BB assumes that momentary servo performance equals one-shot. I did some experiments a few years ago and seem to recall that one-shot performed better on stationary objects than servo did.

From what I've read single shot is better for stationary subjects but I haven't conducted any tests myself...I'm sure someone who has will reply, as I would also like to know...

n1as wrote in post #17814156
Does the camera AF stationary objects as accurately when momentarily focusing in servo as it does in one-shot? The idea that BBF allows both one-shot and servo just by holding (or not) the BB assumes that momentary servo performance equals one-shot. I did some experiments a few years ago and seem to recall that one-shot performed better on stationary objects than servo did.

This article explains it pretty well http://www.canonrumors​.com/forum/index.php?t​opic=20182.0

n1as wrote in post #17814156
Does the camera AF stationary objects as accurately when momentarily focusing in servo as it does in one-shot? The idea that BBF allows both one-shot and servo just by holding (or not) the BB assumes that momentary servo performance equals one-shot. I did some experiments a few years ago and seem to recall that one-shot performed better on stationary objects than servo did.

don1163 wrote in post #17814164
From what I've read single shot is better for stationary subjects but I haven't conducted any tests myself...I'm sure someone who has will reply, as I would also like to know...

I've read this over the years and honestly I can't either way. I've never taken the time to do a side by side comparison. I started using BBF exclusively in AI Servo mode close to 10 years ago and I never noticed any difference in my keeper rate. For my purpose the benefits of BBF far outweigh the odd missed focus, even if that is a real issue. On a purely logical level if AI servo can nail focus on a fast moving, erratic subject it does't really seem that much of a stretch for it to be able to nail focus on a stationary subject.

I'd also like to point out that even if you choose to use one shot over AI servo BBF still offers a distinct advantage. Most lenses are capable of manual focus so if conditions won't allow your camera's AF to lock onto a subject you can still focus manually and activate the shutter quite quickly. You don't have this freedom with focus on the shutter button.

I suppose think it depends on the camera, but a 1D in AI Servo pretty much tends to nail AF just fine. Never really had much need for single shot unless the situation called for a different approach.

I balked at first, just could not perceive any possible "benefit". Then I did it, that was about 18 months ago, and haven't ever looked back.

Once you start actually using it in the field you really begin to see the advantages.

urbanfreestyle wrote in post #17804831
Just wondering how many people on here use back button focus on their camera? I have never used it before but seen a lot of videos from people saying it is the way forward!?

So do you or don't you and why / why not?

Don't think anyone can say "It's the way forward", it depends on the application of what you use your photography for. Some use manual focus, some use shutter release button

If your application is to use that function, by all means use it, but the "way forward"? A bit too far

I never quite got why the manufacturers made lenses with Full Time Manual focus abilities. if the camera will insist on refocusing every time you take your finger off the shutter button, what point does it have. I have only just recently got a lens that offers FTM, and even though I have used BBF ever since I have had a camera that offered BBF (I shot for about seven years with a 300D, so no BBF available, even with the hacked firmware). It is only thinking about things reading this thread that the lightbulb moment happened. BBF allows you to use AF AND FTM to make manual adjustments as part of the same process.

Oh I use the * button on my 50D and swap AE Lock to the AF button, so that I can still focus when using the vertical buttons on my BG-E2N grip. I think the later cameras have an AF button on the grip too don't they? The 20D, which the BG-E2 was designed for didn't have the AF button, so obviously didn't get one. Nice of Canon to keep the same grip for the 30/40/50Ds as well, made upgrading to a 50D an easy choice with almost all identical accessories.

I usually use BBF with AI Servo, but do switch to One Shot when using a flash with external focus assist in low light/contrast situations. You have to do this as Focus Assist is disabled by using AI Servo mode. I don't know why they couldn't incorporate the AF assist beam for use with AI Servo too though. Start the beam when you press the AF/* button, momentarily switch it off as the shutter fires. OK it would be more of a drain on the batteries in the flash, but son't most people use rechargeables anyway? I know I have been using rechargeable AA cells in flash guns since 1980 or so. They're not nearly so expensive now either so having an extra set will hardly break the bank. I can get a set of 800 mAh Ni-MH aa cells ready charged, for my Sigma DG500 speedlight for £2, well actually it's two two packs from Poundland. Handy in an emergency if you need some batteries though.

Alan

The only time I've really used the full time manual focus ability on any of my lenses is to nudge focus while AF is struggling, and find it especially useful on my Sigma 150-500 from time to time when shooting in an environment with tons of contrast as a wide range of distances. (Such a shooting from within tall grass across a pond with a stand of trees in the background.)

Often it is simply faster for me to flick the focus ring with my finger to ballpark the focus back to where I want it if it has managed to catch on something in the near ground or far background of a scene than it is to try and get the autofocus to sort itself out.


I suspect that I won't go back to linking focus, shutter, and meter into the same button, and about the only advantage I've found to using One Shot over AI Servo is being able to trigger focus assist lights. AI Servo shouldn't really function any differently than One Shot once you release the button after all.


If I'm somewhere that has focus fluttering, such as due to things coming between me and the subject, then I find that I can better control focus timing with AI Servo and back button focus on single point than I've been able to do with One Shot focus (I just find it slower to recover from a miss focus on it, and easier to mess up my focus once I locked it if I'm using one shot while AF-meter-shutter are on the same button.)

AZGeorge wrote in post #17805779
I've used BBF for year because, for me, it works as an easy way to mentally and physically separate the decision of focus from exposure and composition.

This is why I do it. I don't like focus and exposure both tied to the same control. I think that comes from starting out as photography hobbyist in the 1970's with a completely manual SLR, and preferring to mimic that with my 60D. I do use AF because it works better than my aging eyes, but otherwise I shoot in manual with BBF.

Tom Reichner wrote in post #17813229
Well, yes, of course you, or anyone, would be using AI Servo in that scenario. . That is what back button focus is all about, using BBF with AI Servo. . I have never heard of anyone using BBF with one-shot mode (although I'm sure someone has done it at some point in time). . It's pretty much assumed that when someone mentions BBF that they are doing it in conjunction with AI Servo.

n1as wrote in post #17814156
Does the camera AF stationary objects as accurately when momentarily focusing in servo as it does in one-shot? The idea that BBF allows both one-shot and servo just by holding (or not) the BB assumes that momentary servo performance equals one-shot. I did some experiments a few years ago and seem to recall that one-shot performed better on stationary objects than servo did.

don1163 wrote in post #17814164
From what I've read single shot is better for stationary subjects but I haven't conducted any tests myself...I'm sure someone who has will reply, as I would also like to know...

I use BBF both ways. Servo works great on moving subjects, but I've had some issues in the past with missing focus on still subjects. Maybe operator error, maybe doing something not quite correctly in servo. I don't know, but when I'm doing landscapes, I use one shot, aimed at the point that works for the scene, then I don't touch the button again.

I've never seen an effective issue with Servo vs. One Shot and BBAF. I think a much bigger issue is getting used to the camera's AF performance and knowing (1) the timing of getting/tracking focus when you press the button and (2) the size/shape of the AF point so you can get it accurately on the subject. Once I am comfortable with a camera's behavior it doesn't seem to matter to me. It's so handy to be able to stop/restart focusing on a moving group of subjects and lightly hold pressure on the release while waiting for the right composition, that I don't think I could effectively use the all-in-one shutter release AF mode any more.

One thing I did on my 5D3 and 7D2 is set the DoF preview button to switch between Servo and One Shot, just in case - but I rarely use it.