Object tracking - anybody uses it successfully?

[zackiedawg]

Thanks Justin, very nice photos as usual! Number two is about the situation I'm talking about, which gives me a hard time.

I figured it was more the birds closing on you than the ones flying parallel - those are always the most difficult since they do rely on the AF system being able to adjust for them as they close. Certainly this is where the A580 easily beats the NEX - in AF-C mode, I can keep focus on a closing target even going 30-40MPH with a screw drive lens - the NEX focus is nowhere near fast enough to track closing motion like that, so it's more of a focus-once-shoot-focus-again type system you have to use, in AF-S mode rather than AF-C. The A77 though should be OK with AF-C mode - as fast or faster than the A580, even with screw drive.

To be fair to the A77 it has to be said that the birds I'm photographing are more often raptors than ducks, flying in more random patterns, and are usually quite far away, which makes it much more confusing for the camera.

I would definitely have a harder time tracking a raptor diving down for a mouse, or a small sparrow erratically flitting all over the sky after insects - those are the shots I generally stick to the DSLR for.

But there are situations where the camera really should focus on the bird (center point right on it), but for some reason picks up only on the background... either because the subject is not big or contrasty enough, or because the background has more clutter to pick up onto than the bird.

That's actually a bit surprising - I wouldn't think the spot focus point would be any different in size than that of my A580, and it does a very good job of isolating a small target against a cluttered background...presuming of course that I do MY job of keeping the focus point on the target.

One thing I find helps is to keep the aperture as big as you can - the more you can narrow the DOF, the more distinction you can put between the subject and the background - once you acquire on the subject, if the background is completely OOF it makes it a little less likely the camera will jump to focusing on the background at the first tiny miss of the focus point...if the background is not far off enough or blurred enough, then the camera may be tempted to switch to it more quickly.

Instead of a not very useful obejct tracking feature it would have been nice to have adjustable focus sensitivity and size in the A77. (But of course that wouldn't sell well in the marketing.) To me, the AF points seem soemtimes too big for precise focusing, and there is no way of keeping the camera from jumping focus on anything passing in the forground (like branches or telphone cables), or nervously going back and forth between the subject and the background, because of the photographer's imprecise tracking. A programable delay in focus aquisition (1 or 2 seconds before jumping to a near/far focus) would be very welcome in this situation.

Another thing I tend to do is make use of the focus hold button. When I'm tracking a small erratic subject like a swallow or swift, which are constantly changing direction and speed, I keep my finger hovering over the focus hold button on my lens...if I sense a sudden directional change occurring that I know I'm not going to be able to keep in frame, or sense the camera attempting to change focus to background because I didn't have the point on target, I press the focus hold which halts the focus activity, and release it when I've got the point on the target again. I'll sometimes use focus hold as the subject takes on a brief straight line or consistent distance to camera, to tell the focus system to 'butt-out' and not attempt to refocus if I stray a bit from the point. In a way, this is like a manual version of what you're describing - it's a way of introducing a delay or pause in the continuous focus, though it's up to you to initiate it.

--
Justin
galleries: http://www.pbase.com/zackiedawg

 

[CatStevens11]

Very useful tip!
Thanks!

 

[quatpat]

Thanks Justin, very nice photos as usual! Number two is about the situation I'm talking about, which gives me a hard time.

I figured it was more the birds closing on you than the ones flying parallel - those are always the most difficult since they do rely on the AF system being able to adjust for them as they close. Certainly this is where the A580 easily beats the NEX - in AF-C mode, I can keep focus on a closing target even going 30-40MPH with a screw drive lens - the NEX focus is nowhere near fast enough to track closing motion like that, so it's more of a focus-once-shoot-focus-again type system you have to use, in AF-S mode rather than AF-C. The A77 though should be OK with AF-C mode - as fast or faster than the A580, even with screw drive.

Well, it depends... for the camera the incoming bird is definitely more challenging, but for the photographer it might be easier. But again, it all depends on the bird, size and distance, the ones I'm usually trying my luck on do not fly in very predictable patterns, and make smooth tracking difficult.

To be fair to the A77 it has to be said that the birds I'm photographing are more often raptors than ducks, flying in more random patterns, and are usually quite far away, which makes it much more confusing for the camera.

I would definitely have a harder time tracking a raptor diving down for a mouse, or a small sparrow erratically flitting all over the sky after insects - those are the shots I generally stick to the DSLR for.

Those are the shots I'm talking about - low flying, hunting raptors are very difficult to track successfully, both for the camera and the photographer. I have rarely had much success with them as long as they were in front of a non-sky background.

But there are situations where the camera really should focus on the bird (center point right on it), but for some reason picks up only on the background... either because the subject is not big or contrasty enough, or because the background has more clutter to pick up onto than the bird.

That's actually a bit surprising - I wouldn't think the spot focus point would be any different in size than that of my A580, and it does a very good job of isolating a small target against a cluttered background...presuming of course that I do MY job of keeping the focus point on the target.

Well, it actually happens more often with the A77 than with the A350... that's why I'm wondering whether the focus points are a bit on the large side when the subject is at a certain distance.

One thing I find helps is to keep the aperture as big as you can - the more you can narrow the DOF, the more distinction you can put between the subject and the background - once you acquire on the subject, if the background is completely OOF it makes it a little less likely the camera will jump to focusing on the background at the first tiny miss of the focus point...if the background is not far off enough or blurred enough, then the camera may be tempted to switch to it more quickly.

I only shoot my 4.5/400mm wide open, since anything else would be an insult to that lens...!

Instead of a not very useful obejct tracking feature it would have been nice to have adjustable focus sensitivity and size in the A77. (But of course that wouldn't sell well in the marketing.) To me, the AF points seem soemtimes too big for precise focusing, and there is no way of keeping the camera from jumping focus on anything passing in the forground (like branches or telphone cables), or nervously going back and forth between the subject and the background, because of the photographer's imprecise tracking. A programable delay in focus aquisition (1 or 2 seconds before jumping to a near/far focus) would be very welcome in this situation.

Another thing I tend to do is make use of the focus hold button. When I'm tracking a small erratic subject like a swallow or swift, which are constantly changing direction and speed, I keep my finger hovering over the focus hold button on my lens...if I sense a sudden directional change occurring that I know I'm not going to be able to keep in frame, or sense the camera attempting to change focus to background because I didn't have the point on target, I press the focus hold which halts the focus activity, and release it when I've got the point on the target again. I'll sometimes use focus hold as the subject takes on a brief straight line or consistent distance to camera, to tell the focus system to 'butt-out' and not attempt to refocus if I stray a bit from the point. In a way, this is like a manual version of what you're describing - it's a way of introducing a delay or pause in the continuous focus, though it's up to you to initiate it.

There you got me. I never use those focus hold buttons, although I know I should learn to use them. The only problem is that whenever I think of using them, it is because the focus has already shifted to the famous telephone cable / branch / ugly factory chimney in the fore/backround. But if I had more training, I would probably see these things coming with the other eye... and that's another thing I have to learn. Nevertheless, a focus sensitivity adjustment on a high-end APS-C like the A77 would be a nice thing to have.

qp

--
Justin
galleries: http://www.pbase.com/zackiedawg

 

[quatpat]

Sorry, the first part of my reply should have gone to OntarioJohn.

I hadn't thought of this particular situation ever before, but I'm glad that it worked out for you! Good to see that there is at least on situation where the feature delivers.

I agree also with Seilerbird666 that the feature is probably more effective on wide angle or short tele lenses, which can be hold relatively steadily, or which are used on a tripod.

S

 

[quatpat]

I just took a few test photos this morning, and here is a perfect example of what I mean by "smaller focus points would be useful".

It's actually not so much the indicated focus points in the viewfinder that are too large, but rather the actual focus area of each point. Or in other words: the actual focus sensitive area of each point is quite a bit larger than indicated by the points in the viewfinder. This can be good in some situations, but also very annoying in others, typically when you want to shoot a small bird across branches in a tree or a bush.

In the example below, the camera was set to spot focusing with the central AF-point, and the yellow square is approximately the size that the central focus point shows in the viewfinder. It fitted easily in between the wires, yet there was no way to make the camera focus on the window frame of the house in the background. In this situation I would have to use manual focus as an only alternative, or to place the focus point somewhere else, outside of the wires.

I then tried to focus on the balcony and tiles on the left side of the house, still between the wires, with the result that the AF would nervously jump back and forth between the wires and the house.

Conclusion: it would be nice if Sony would implement an option to reduce the acutal AF-sensitve area, so that AF remains possible in situations like this. However, this is probably hardware related, and won't be an easy fix through firmware update.

Full frame:





100% crop:





qp

 

[zackiedawg]

Again, interesting to me, because I shoot in these types of focus situations routinely as a birder. I can't tell you how many times I needed AF to grab the eye of a bird slotted in between reeds or branches, or through a veritable tunnel of vegitation. It's never been a problem on my A550 or A580 in spot focus mode.

That'd be my only main question: were you in 'center focus' or were you in 'spot focus' using only the center spot? I could see 'center focus' missing that one easily, but I would expect spot focus to have no problem threading those telephone wires and focusing on the building. But again, I'm basing it on my experience with my A580, and not having familiarity with the A77 and whether it functions differently in spot or has a larger spot area.

I often crop my wildlife and bird photos - anywhere from 20-50%, mostly for composition when I have to shoot fast and don't have time to frame for thirds, or to crop out a distracting element...as well as to get a little closer. Virtually all of my still bird shots are shot using spot focus, center-point, AF-S...and very often are threading into spaces smaller even than the gap between wires you showed in your sample, and while I don't know if I can say I've never had a focus miss, I'd say I virtually never do - it's extremely accurate in threading through some very tiny holes to focus where I need. Here are a few of those that I tend to call 'thread-the-needle shots':





In these cases, uncropped, the spot focus square was barely on the animal's face - I had an area no larger than the square's height in any direction before it overlapped something in the foreground just waiting to steal focus.

I wonder then, is the A77's 'spot' actually covering a larger area than that of the A580? if anything, I'd almost have thought less so, given the higher res which could allow more accurate definition of the covered pixel area.

--
Justin
galleries: http://www.pbase.com/zackiedawg

 

[quatpat]

Nice shots Justin, I add another two of mine here, taken in similar situations... in these cases my old a350 didn't have much of a problem to AF on the birds (these photos are heavy crops as well), while I cannot tell whether the A77 would have easily allowed the same here. From my experience (not direct comparison), it seems to me that the A77 more often than the A350 picks up objects which are close to the focus point, but not acutally on it. This is not always a handycap, in particular with BIF against the sky, but it is one in the "shoot through vegetation" and "BIF at a distance in front of a non-sky background" situation. Ideally I'd prefer to have the option to chose between a small and large central AF area via the menu, but if this is not possible, I'd rather go for a small one.

Concerning my test photos I believe that I was in "local", with the center spot selected. However, I will have to repeat the test tomorrow in order to see wheter there is any difference in behaviour between "local" with the center point and "spot" focus. I will also compare the behaviour of the A77 with the one of the A350, with the same lens, in order to make sure that the difference is not all just in my imagination.

qp

 

[zackiedawg]

Nice shots - so you have threaded-the-needle successfully with the A350 but seem to have more difficulty with the A77. That's definitely interesting.

I am curious to see what becomes of the tests - comparing local/center versus spot/flex spot (if you weren't already in it) and against the A350. I can't recall ever having issues with this on my A300 either - spot focus was always able to focus on the smallest of areas very accurately. Possibly if the A77 was in a local/center setting where more than just the one spot was active or contributing to focus, that could have been the issue - but if you were in spot focus and those telephone wires caught the focus that far from the point, that would seem to be quite a problem.

Best of luck - looking forward to your test results.

--
Justin
galleries: http://www.pbase.com/zackiedawg

 

[quatpat]

I did the tests this morning, as I said.

The results have confirmed my initial impression, which was that the central AF area of the A350 is probably smaller than the one of the A77, in relationship to frame. Also the indicated square in the viewfinder is slightly smaller.

Here are the results, done with the A350 and the A77, and the Minolta 400/4.5, and the Tamron 200-500mm:

A350 + Minolta 400/4.5

• No difficulties in focusing in between the wires with both, spot focus and local with center point selected. It was not possible to focus on the wires at all though.

A77 + Minolta 400/4.5

• Doesn't focus through the wires as long as the target is the window frame, but does when aimed at the balcony on the left side, which has more detail to pick up. No difference between spot focus and local with center point selected.

A350 + Tamron 200-500mm @ 500mm

• Again, no difficulties in focusing in between the wires with both, spot focus and local with center point selected. It was not possible to focus on the wires at all.

A77 + Tamron 200-500mm @ 500mm

• Occasinally focuses through the wires on the window frame, probably because of the bigger magnification, but most of the time still focuses on the wires. No problem to focus through the wires on the balcony. No difference between spot focus and local with center point selected.

Conclusion:

As it seems, the A77 has a more sensitve AF (picks up on the thin wires, while the A350 cannot), but also a quite a bit bigger sensitive central area, which is a handicap when shooting through foreground obstacles like vegetation or wires. This is rather strange to me, because one should think that if anything, the A77 as the higher end model should have a more precise central AF-point than the A350. However, despite it probably being more sensitve, it's bigger size makes it less useful in practical use when precise spot focusing is necessary. Again, a possiblity to chose a smaller central AF-area via the camera's menu would be nice.

Here are some typical images of the test: first the A350, then the A77, both with the Minolta 400mm (sorry for the shadow on the left, my own window frame got into the A350 shot):

A350 always focuses through the wires with the Minolta 400mm:





A77 almost never focuses through the wires with the Minolta 400mm:





Not related to the initial test, but here is another interesting observation: The A77 + Minolta 400/4.5 record slightly more detail at pixel level than the A350 + Tamront200-500mm at 500mm. That's pretty impressive from the Minolta lens, considering the more densely packed sensor of the A77, and the 100mm differcence in focal lenth. The result is close however, and the advantage mostly due to the Minolta lens being slightly sharper, and having better micro contrast. And of course, it can not be ruled out that there are slight differences in focus between the two examples. They were the best ones of a series with each combo.









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