I specialize in photographing birds in flight and I make a living teaching others how to do the same. One of the techniques I use I call bumping the focus. This technique is often mis-understood and I get alot of questions about it. I just finished a lengthy answer to a question in another thread, so I thought it would be usefull to post my answer here as well where it would be easier for folks to find in the future. Here it is:
There are three different uses for the bump focus technique. I will try to explain each of them below. By bumping I simply mean letting off the focus and then refocusing quickly.
1. The first reason to bump the focus is to prefocus. The first task when photographing a BIF is to aquire it in the viewfinder and focus on it. It is beneficial to be able to do this as quickly as possible. When using long focal lengths, the bird may be so out of focus that you can't see it in the viewfinder even if it's there. Then when you do get it in the viewfinder it may take much longer to focus on it if the foicus is set to a drastically different distance. To overcome these issues, I will prefocus at the approximate distance that I anticipate for my subject. Then when the subject arrives, I can find it and focus on it quickly. I prefocus the camera by pointing the camera at something at the desired distance and then I focus on it. Now I'm ready for a BIF at a similar distance. If I need to switch the distance I will simply point the camera at something at the new distance and bump the focus. This will prefocus the camera at the new distance. Photogs that use a tripod will often prefocus manualy. Since manual focus is difficult hand held with big glass, I use the bump to prefocus.
2. When I am tracking a BIF against a varied bg and I miss and focus on the bg I will bump the focus to quickly return focus to the bird. Bumping the focus overrides the delay set by the tracking sensitivity custom function. I set this tracking sensitivity to slow to get the longest delay possible. This helps when you are focused on the bird and want to avoid focusing on the bg, but it hurts when focussed on the bg and you want to return focus to the bird. Bumping the focus overrides the delay.
3. This is the most important use of the bump technique. Most photogs will aquire focus on a bif and then try to continously maintain foucs while they are tracking and watching the bif in the viewfinder. They tend to focus continuosly waiting for the moment they wish to make a photograph. Often while watching, tracking, and waiting for the moment, the photographer will miss and focus on the bg. This is extremely easy to do when the bif is flying against a varied bg. This is the reason it is so much more difficult to photograph BIF against a varied bg as opposed to smooth sky bg. When the focus grabs the bg, then the photographer needs to re-aquire focus on the bif. This may take too much time causing the photog to miss the critical moment. I try to avoid this by only focusing on the BIF when I'm sure I'm on target and during the critical moments when I'm acualy making images. So, what I will typicaly do is aquire the bif initial and focus on it. Then I will let off the focus and just watch it in the viewfinder while tracking it visualy only. As the distance changes, the BIF will start to go out of focus. When that happens I bring it back in focus by quickly making sure the AF point is on the biurd and then I bump the focus to get it in focus again. I do this repeatedly as I'm visualy tracking the bird. When the BIF gets to the spot I want to start making pictures, I wil focus and shoot all at once. I shoot in short controlled bursts trying to time the critical moments with the best wing positions, etc. Because I have bumped the focus along, the focus is very close to where it needs to be when the moment to make pictures arrives. Then when I focus and trip the shutter it happens very quickly. If I tried to focus constantly while the bif approached I would likely miss, focus on the bg, and miss the critical moment. My goal is to keep the bird close to in focus and in the viewfinder without focusing on the bg and to do this up until the critical moment arrives. Then I try to maintain the focus while making great pictures. Bumping takes lots of practice, but if you develop this skill, it will make your keeper rate go way up.
Greg Schneider wrote:
Sounds like #1 could be accomplished by the prefocus ring on the superteles. I'm not sure if that's what you're referring to.
That is another way to accomplish pre-focus. Unfortunately, it isn't practical to do it that way when shooting hand held. It works great when using a tripod, but tripods are a handicap when photographing bif.
By "bump the focus" I assume you mean press the autofocus button for a brief instant.
So if tracking a bird with the button completely depressed (AI Servo) and you focus to the background, let off the focus and then press it again to re-establish focus again?
Good tips Jim, thanks for posting. This is the sort of stuff if you do it regularly it's second nature - always harder to explain than actually do. I use the prefocus trick to avoid the lens hunting in busy backgrounds. Superteles have a huge range of defocus and when they go out of focus they really go out of focus and it can be a pain to reacquire focus just keeping the AF button half depressed. Also make sure your using the right distance limiter setting to help.
When you use extended AF (multiple sensors) in AI Servo on Canon DSLRs the camera assumes that the chosen sensor (usually but not always the centre one) is the one that has initial subject acquisition and that the others will only then be used to maintain the tracking of that target. But what if you were just a bit off with your aim ? Not enough to focus on the background but enough to focus on the wrong part of the bird. In that case bumping lets you refine the intended target and better track it.
This can be significant if you activate AF and IS by pressing the AF button (especially when it is the shutter button) before you have aimed the lens. You will have the IS up and running by the time you need it but the AF tracking may be on the wrong target. Bumping lets you fix that.
Note that bumping involves the momentary release of AF before re-pressing the AF button. That release, however brief, will scrap any predictive focus information already obtained by the camera. It may take a few moments for the camera to once again determine the approach speed of the subject and get the predictive focus working again. It might cost you a slightly mis-focused frame before the camera gets it right, particularly if the camera is shooting at a fast frame rate.
I don't know whether or not this applies to Nikon cameras, but it certainly applies to Canon cameras and so deserves to stay in this forum.
When you use extended AF (multiple sensors) in AI Servo on Canon DSLRs the camera assumes that the chosen sensor (usually but not always the centre one) is the one that has initial subject acquisition and that the others will only then be used to maintain the tracking of that target. But what if you were just a bit off with your aim ? Not enough to focus on the background but enough to focus on the wrong part of the bird. In that case bumping lets you refine the intended target and better track it.
This can be significant if you activate AF and IS by pressing the AF button (especially when it is the shutter button) before you have aimed the lens. You will have the IS up and running by the time you need it but the AF tracking may be on the wrong target. Bumping lets you fix that.
Note that bumping involves the momentary release of AF before re-pressing the AF button. That release, however brief, will scrap any predictive focus information already obtained by the camera. It may take a few moments for the camera to once again determine the approach speed of the subject and get the predictive focus working again. It might cost you a slightly mis-focused frame before the camera gets it right, particularly if the camera is shooting at a fast frame rate.
I don't know whether or not this applies to Nikon cameras, but it certainly applies to Canon cameras and so deserves to stay in this forum.
I use the center AF point only when photographing bif. I avoid multiple focus points because I want to have complete control over what trhe camera focuses on. When photographing bif against varied bgs, it is more difficult to maintain focus on the bif if multiple af points are used. The tendency for the camera to focus on the bg is much greater. When photographing bif against sky, multiple af points are helpful, but photographing bif against sky is much easier and the multiple af points aren't really needed anyway. By staying with the center af point only, I am always ready for action regardless of bg. The techniques I described above are all based on using center af only. Using center af only also allows more precision when choosing the part of the bif to focus on.
Lord Fluff wrote:
Doesn't this belong in Nature & Wildlife though?
It could go in either, but I thought it was more about the technique than the subject, so I put it in here. The technique may be usefull for other subjects.
Alan321 wrote:
This can be significant if you activate AF and IS by pressing the AF button (especially when it is the shutter button) before you have aimed the lens. You will have the IS up and running by the time you need it but the AF tracking may be on the wrong target. Bumping lets you fix that.
This is why I use the AF button for AF and the shutter button to activate (but not lock) the meter... it also activates IS. When shooting I half-press the shutter as I bring the camera to my eye, so by the time I'm looking through the viewfinder the IS is already "primed". Makes life a lot easier at 600mm and beyond!
I too use the rocker ring to get the focus close before trying to acquire focus with AF. I usually have focus preset set to near infinity, which is about where most wildlife tends to hang out. I haven't tried using the AF button approach, but it seems like a good idea to give a bit more control than the rocker ring (as you can stop before you hit infinity).
I do a similar thing to what Jim describes when shooting macro. When I'm shooting with a flash bracket I often don't have a hand free to turn the focus ring. When I want to adjust magnification I tap the AF button briefly. AF hunts out towards infinity (slowly... this is a 100/2.8!) and I usually get close enough to the magnification I want to avoid playing with the focus ring.
JimN wrote:
It could go in either, but I thought it was more about the technique than the subject, so I put it in here. The technique may be usefull for other subjects.
The Nature & Wildlife is an Presentation forum that's where you post your pics. All gear & technique talk for Canon is in this forum
that's where you post your pics. All gear & technique talk for Canon is in this forum