AF Speed: Do You Have It All Wrong?
- Thread starter Steve
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Another great tutorial!
Love the focus-limiter tip... 30+ years of long-lens photography, and I think I can count on one hand the number of times I used a focus limiter. Seeing the pick-up truck was the perfect graphic to remind me how close 0 to 10M is.
Ever since moving to mirrorless, I've worked with my thumb on the MF ring, this has been the key to preventing mis-focus to background... with the thumb in override position, it is easy to get the camera to move off the wrong target.
cheers,
bruce
Nice work, good info Steve. I never really thought about how fast a subject coming at me would have to be for the lens not to keep up but I'm not surprised by your findings. I think there would be plenty of complaints if lenses were generally too slow to keep up with most subjects. What I have found is faster AF reduces initial acquisition time which your findings confirm. The 600PF is the fastest focusing lens I have (and boy is it fast) but I will be using the focus limiter more often now after watching your video...
Thank you for the video Steve very well done!
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Thanks!
Also, just FYI, the truck is 6m like the 180-600 range limited MFD, not 10m. Figure a truck and a half
Thanks!
Also, just FYI, the truck is 6m like the 180-600 range limited MFD, not 10m. Figure a truck and a half
Right... of course, that would be a real stretch truck at about 32'... A whole new meaning for "Monster Truck." 
Robert S
Well-known member
Thanks for the video. I don't have much luck with birds in flight when the are coming at me. I don't know what is going on inside the camera when I press the shutter button. I assume the auto-focus continues to do its thing so I need a high shutter speed to 'freeze' the moment. If I have this right then taking photos of BIF coming at me is similar to taking a photo of a bird flying across the focused plane [ might have the words wrong but at right angle to me ] but not panning. If I have this right then I need a very fast shutter speed to stand a chance of getting a reasonable result.
What would be a max shutter duration to freeze motion? Maybe I should make sure the shutter speed a 1/2500 sec or faster.
What would be a max shutter duration to freeze motion? Maybe I should make sure the shutter speed a 1/2500 sec or faster.
If birds are coming right at you shutter speeds on the order of 1/3200" or even 1/4500" are helpful especially if the birds fill much of the frame.
Robert S
Well-known member
Thanks Dave. It seems that is what I was doing wrong. Live and learn eh. Seems obvious when you think about it, but I didn't think about it. Guess watching the video was well worth it. Next chance I get I'll up the shutter speed.
Excellent video I have overlooked the focus limiter on the lens. I was accepting the fact that my 200-500mm lens was just slow to lock. I took it off full and Wham, presto change-o Much faster.
Thanks Steve.
Here's an excerpt from my BIF book that talks about shutter speed - but the bottom line is what Dave said
When you’re panning with the bird (like from side to side or even coming in at an angle), you’re helping to compensate for most of its movement by (hopefully) keeping him more or less in the same position in the viewfinder. However, when it’s coming straight at you, that flies out the window.
Think of it this way…
Let’s say you have a larger bird clipping along at roughly 25MPH. If you’re panning from side to side it’s not unreasonable to assume that even a semi-experienced shooter can manage this at as little as 1/1600th and still secure a few sharp images (depending on the distance, which we’ll discuss soon). If your BIF experience level has a bit heavier seasoning, you can probably even manage a nice number of sharp images at just 1/500th ~ 1/1000th.
However, if that same bird coming right at the lens at 25MPH, it’s covering 36.6 feet (11.15m) every second that ticks off the clock - figure about 440 inches (1.11m) per second. So, at 1/500th of a second, you’re getting just under an inch of movement. One inch of movement from a bird coming at the camera is definitely going to display a disappointing amount of blur.
In fact, I think we can agree that even a quarter inch of motion during exposure would probably still be visible with a target coming towards the camera (1/1600th ~ 1/2000th, approximately). To dip down to 1/8th inch of movement, you’d need 1/3200 ~1/4000th of a second - and that’s still straddling the border between acceptably and unacceptably sharp (1/16th or less is better). That’s a far cry from the 1/1600th “safe” speed that would normally work for this kind of bird if you could pan along and keep the target in roughly the same spot in the frame.
Whew, excellent reply....!!Here's an excerpt from my BIF book that talks about shutter speed - but the bottom line is what Dave said
When you’re panning with the bird (like from side to side or even coming in at an angle), you’re helping to compensate for most of its movement by (hopefully) keeping him more or less in the same position in the viewfinder. However, when it’s coming straight at you, that flies out the window.
Think of it this way…
Let’s say you have a larger bird clipping along at roughly 25MPH. If you’re panning from side to side it’s not unreasonable to assume that even a semi-experienced shooter can manage this at as little as 1/1600th and still secure a few sharp images (depending on the distance, which we’ll discuss soon). If your BIF experience level has a bit heavier seasoning, you can probably even manage a nice number of sharp images at just 1/500th ~ 1/1000th.
However, if that same bird coming right at the lens at 25MPH, it’s covering 36.6 feet (11.15m) every second that ticks off the clock - figure about 440 inches (1.11m) per second. So, at 1/500th of a second, you’re getting just under an inch of movement. One inch of movement from a bird coming at the camera is definitely going to display a disappointing amount of blur.
In fact, I think we can agree that even a quarter inch of motion during exposure would probably still be visible with a target coming towards the camera (1/1600th ~ 1/2000th, approximately). To dip down to 1/8th inch of movement, you’d need 1/3200 ~1/4000th of a second - and that’s still straddling the border between acceptably and unacceptably sharp (1/16th or less is better). That’s a far cry from the 1/1600th “safe” speed that would normally work for this kind of bird if you could pan along and keep the target in roughly the same spot in the frame.
Love the math...
hrv
Well-known member
@Steve I have a question.
Looking at your video, everything makes sense. But my experience has been that it is really challenging to photograph birds that launch from their perch and get sharp pictures.
The gear isn't the problem, Z9, fast glass.
But when for example a woodpecker launches from a tree I can see in NX Studio that the focus point is still near the tree, not following the bird, at least not fast enough.
Now this is all pre 4.1 firmware, and I deleted all those files so cannot post an example, but in all cases I was 100% locked on to the bird and both with Wide Custom as well as 3D, the camera/lens would not be able to focus on the bird flying away.
Any thoughts on what I would be doing wrong?
Looking at your video, everything makes sense. But my experience has been that it is really challenging to photograph birds that launch from their perch and get sharp pictures.
The gear isn't the problem, Z9, fast glass.
But when for example a woodpecker launches from a tree I can see in NX Studio that the focus point is still near the tree, not following the bird, at least not fast enough.
Now this is all pre 4.1 firmware, and I deleted all those files so cannot post an example, but in all cases I was 100% locked on to the bird and both with Wide Custom as well as 3D, the camera/lens would not be able to focus on the bird flying away.
Any thoughts on what I would be doing wrong?
I call that AF surprise
The truth is, sometimes the bird moves faster than the camera can react.
Here's another excerpt from the BIF book that talks a little about it.
For takeoff shots, the more shutter speed you can marshal, the better. The problem we’re facing is simple - when the bird takes off, you’re not panning yet. With a normal BIF shot, we can use more reasonable shutter speeds since our panning efforts help to keep the bird in (more or less) the same position in the frame. In fact, that’s why experienced shooters can often dabble in surprisingly low shutter speeds and still send a series of acceptably sharp images to the card.
However, we don’t fully enjoy that advantage at takeoff.
When the bird launches, it’s accelerating and although we attempt to move with it, it’s simply not as refined as a regular pan. So, it generally takes more shutter speed than you’d expect.
The actual shutter speed will vary by species and generally the larger the bird, the slower you can drop (since their takeoffs aren’t as quick). As a general guideline, I tend to at least double the speed I’d typically use for panning with a given species. So, if I like 1/2000th of a second for normal panning with a specific bird, I’d prefer 1/4000th (or higher) for takeoff.
AF Surprise And Smaller F/Stops
The second challenge that comes into play with takeoff shots is autofocus - and the fact it can struggle to keep up.
Before we get too far, keep in mind AF prowess and success varies wildly by camera, and by the kind of bird in your viewfinder. Some cameras are better at sticking with a given species at takeoff than others.
The problem I’ve seen over the years amounts to what I like to call “AF surprise,” and it’s just what it sounds like. The camera is focused on a stationary subject and suddenly the target and your rig are both in motion. In some cases, it takes the camera a split second to react to this sudden change in circumstance and if the bird doesn’t stay precisely on the current focal plane (something they are remarkably resistant to doing), you end up with a near-miss.
It’s equally possible that, in the frantic viewfinder confusion that inevitably follows a takeoff, the AF area is no longer in the optimal place anymore. So, instead of the head and neck region, maybe it’s on a wing or background as you shoot.
The solution that sometimes works for me in this scenario is simple - I drop the F/stop.
Don’t get me wrong, I don’t go crazy or anything, usually not much more than going from F/4 or F/5.6 to F/8, but it does give you a little breathing room for a slight AF miss.
Putting It All Together
If I’m trying to land a takeoff shot, I’ll usually choose a medium-sized AF area for a little extra tracking latitude during takeoff.
For AF placement, it helps to visualize what the bird will look like as it takes off and where its head and neck area will sit in the frame. I always plan a little wiggle room in both AF position and crop (I typically crop a little looser for takeoff shots since wing position is more challenging to determine.) Ideally, I like to compose so I can engage and lock AF on the head before takeoff - it seems to help the AF system stick with the proper target.
Also, don’t underestimate the amount of space necessary for the bird to fly into - it’s easy with takeoff shots to wind up with the bird’s head too close to an edge with lots of empty space behind it. Remember - the bird may drop or spring upward at takeoff, not necessarily launch just straight out from the perch.
If your bird is on the water, remember to leave a bit of room behind it for the inevitable splashes that come as it struggles to get airborne.
For this shot, I kept the crop a little loose so I have enough space in front of the cormorant and not cut off the splash behind him. Sony a1, 400mm + 1.4TC, 1/3200th, F/4, ISO 1250.
In addition, frame the composition based on the size of the airborne bird, not the version sitting on the perch - they get a lot bigger when they fly. More than once I thought I was at a perfect distance only to end up with a sad collection of clipped wings once my avian friend hit the skies.
Although this hawk looks too small while perching, he fills up a lot more frame once in flight. Make sure you account for the size of a flying bird when considering your distance / lens / crop.
As discussed, before takeoff I’ll goose my shutter speed and drop my F/stop a little. Of course, the ambient light conditions get a vote here, but do what you can. In my experience, a faster shutter speed is a slightly higher priority than F/stop (especially if you’re at more of a distance, since you’ll have the extra depth of field that rides shotgun).
Once the bird launches, do your best to keep that AF area on its head - or at least on the body. And prepare yourself: takeoffs unfold at a surprisingly chaotic pace! Following the recommendations we just covered should give you the best chance for a successful photo.
hrv
Well-known member
One more thing on @Steve's summary above. Just like the question of a bird flying straight towards you instead of tangential to you in terms of shutter speed, changes in focal plane distance happen a lot faster as dynamic subjects move more towards you instead of across your field of view. That applies to take off shots too, my best results on take off shots are when the bird launches across my field of view just like a panning shot. If they launch a bit towards me it still can work but it's really hard for the AF system to go from zero to full tracking when a bird launches right towards me or at angles that are near to being right towards the camera position.
So in addition to the great advice above, it can pay to think of wind direction and most likely launch direction (larger birds often launch into the wind) and position yourself accordingly if the light and background still works.
Dinusaur
Member
Another factor that comes into play is the individual 'reaction time'. After the light hits one's retina it takes 30 ms to reach the brain which then takes time to process before sending command down one's arm to finger tip for shutter release and that's another 200 - 400ms depending on one's reaction time. And that can easily cause the bird to miss the focal plane as you said. This 'reaction time' is the reason we often take extra few frames even after the bird or subject disappeared from view. At z9 frame rate this could be easily 7-8 frames. That's why the saying goes that we always live in the past. Here's an example of that :I call that AF surprise
The truth is, sometimes the bird moves faster than the camera can react.
....
The problem I’ve seen over the years amounts to what I like to call “AF surprise,” and it’s just what it sounds like. The camera is focused on a stationary subject and suddenly the target and your rig are both in motion. In some cases, it takes the camera a split second to react to this sudden change in circumstance and if the bird doesn’t stay precisely on the current focal plane (something they are remarkably resistant to doing), you end up with a near-miss.
....
One way to counter this will be to start shooting before the bird actually takes off - they do give some indications of when they are about to leave the perch.
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LOL, been there, done that! I always start popping off shots when I see the "squat" just before liftoff
hrv
Well-known member
I have had success with larger birds, but not with smaller ones. They are just so darn quick.
It takes a lot of practice. Until and unless you can keep the bird at least sort of steady in the frame for a few seconds, it's a roll of the dice. The funny thing is, small birds aren't insanely fast from a MPH standpoint - it's their erratic flight patterns and close-range that really makes them tough!
Replytoken
Well-known member
As others have said, great video. It clearly captured my frustrations with focus acquisition on some lenses rather than the ability to keep focus once a bird is in focus (although that can sometimes be an issue). This may be related or not, but what I do find frustrating is when you are shooting a bird and if for some reason it is either blocked (by a tree or object) or it falls out of the viewfinder, the camera seems to lock up rather than rack through the focus as I would expect when I pull my finger off of the shutter or BBF button. I can understand if it racks through the focus range, limited or not, and not acquire the subject, but I often find the lens just sites there. A good example of this is if you are at the beach and a number of birds are present. Sometimes a bird will peel away and I will want to focus on another one that is either closer or not flying away from me. I am not ruling out user error, but I cannot put my finger on how to understand when this happens. And it happened again today. I was shooting a D500 with a 300mm AF-S f/4 and a 1.4 TC.
--Ken
--Ken
Snapshot2020
Well-known member
Key indicator is when those Raptors “shoot that Squat“ jettison the load before lift off.LOL, been there, done that! I always start popping off shots when I see the "squat" just before liftoff
Replytoken
Well-known member
Would somebody please tell that to the herons as well. Two loads lightened and still no lift-off with one of them that I was watching and waiting for today.Key indicator is when those Raptors “shoot that Squat“ jettison the load before lift off.
--Ken
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LOL, I have a few of those shots!Key indicator is when those Raptors “shoot that Squat“ jettison the load before lift off.
It might be too long of a delay set under blocked AF response. If it's a longer delay, the camera will hesitate before locking onto a new target. Try setting it at 1 or 2 - that's usually how I did with the DSLRs. With mirrorless, I tend to be in the middle around 3 (but it really depends on how sticky I need to to be vs how fast I need to to grab a new target from an old target).