What do you need 51 focus points for ?

[NHL]

philgib wrote:

I was indeed speaking about a bird flying on the same distance from left to right, as it happens most of the time on the beach. when birds like tochase fishes parallelto the shore line

You mean like this?
http://forums.steves-digicams.com/fo...mp;forum_id=11

You don't need 51 AF points for birds chasing the shoreline... In fact if you do use the multiple AF points you would end up getting the waves in the background instead

-> Use the center AF point because it's more accurate plus most of the time you don't know what direction a bird is coming from...



lomitamike wrote:

I've missed many shots because the auto-focus point was focused on something other then what I was trying to focus on. Especially when shooting low light sports or "busy" backgrounds.

-> You would want the AF point to be highly selective
i.e. I use mainly the center AF point and in single shot AF

Continuous AF is nice, but then again if you can't keep the AF point on the bird trajectory then it would track focus on the background instead... You can try both way, but from my experience you'll get more keepers using one-shot AF on smaller birds

[JohnG]

NHL wrote:

You don't need 51 AF points for birds chasing the shoreline... In fact if you do use the multiple AF points you would end up getting the waves in the background instead

-> You would the AF point to be highly selective

Exactly - BUT, that's why it's nice to have MULTIPLE cross-sensor points to choose from - and if possible multiple HIGH PRECISION points. on some of the older DSLRs you're lucky if the center point is high precision and cross type.

So no you don't need 51 - but it sure is nice to be able to select a point OTHER than the center point for larger birds so the framing in-camera is better.

[NHL]

JohnG wrote:

So no you don't need 51 - but it sure is nice to be able to select a point OTHER than the center point for larger birds so the framing in-camera is better.

True

However in nature you don't know which direction a bird will take-off next nor where it's coming from - It's not as if they all fly toward a goal post then it would be nice to preselect another AF point to use...

Most of the time you'll be lucky to frame them at all :-) :lol::-)

[eric s]

I'd like to make a minor correction to something that JohnG said.
High precision cross-type sensors on the Canon 1-series cameras work in "high precision" mode at f/4 and wider. Not f/2.8, as he mentioned. At least this is true of my 1D MkII N.

The non-one-series cameras (40D, whatever the latest D-Rebel is) are only "high precisions" sensors on f/2.8 lenses (as he said.)

This is another subtle way the one-series cameras are better than Canon's other models.

I really, really, really wish they'd find a way to improve this to f/5.6. It's been f/4 for a long time (since long before digital SLRs existed.) I don't know what it up (some of its physics having to do with the size of the depth of field... but I bet some is cost, CPU speeds, battery power limitations.... I wonder if they *could* make it work at f/5.6, but choose not to to save money or meet their price point?)

I generally agree with NHL in the discussion about birds in flight.

Most use only the center AF point when doing BIF if there is any risk of the bird flying near something that the camera could lock on to by mistake (branches in front/behind the bird.)

On the other hand, I know almost no-one who shots BIF of birds as small or smaller than a baseball. They mostly shoot things like raptors or bigger (like heron-sized things.) Sure, it can be done. I've seen flight shots of tree swallows (lucky bastard!) But most people, not even the pros, actually try to do it... they move so fast and eratically that its nearly impossible. Ok, some do it for fun - but they don't actually expect to get the shots.

I spent the weekend shooting hawks from a Mountain. And let me tell you, when the sharp-shinned flys by, you wish you could use AF expansion. Have it lock with the center AF and then continue tracking with the rest of the AF points. But it doesn't work in practice. It will often lock on to the wing (which is closer on a flyby) and you won't get the body in focus. But trying to track something that fast with only one AF point is really hard. I'm certainly not as good at it as I'd like to be.

Eric

Excelent viewpoints & discussion gentlemen (I had to jump in here quick, before Jim wrote a 40 page dissertation on the subject)....lol!

[NHL]

eric s wrote:

On the other hand, I know almost no-one who shots BIF of birds as small or smaller than a baseball. They mostly shoot things like raptors or bigger (like heron-sized things.) Sure, it can be done. I've seen flight shots of tree swallows (lucky bastard!) But most people, not even the pros, actually try to do it... they move so fast and eratically that its nearly impossible. Ok, some do it for fun - but they don't actually expect to get the shots.

How about the size of a tennis ball then, is this small enough?
http://forums.steves-digicams.com/fo...mp;forum_id=11

-> Theses guys have no predetermined fly path, but zig zag on a dime at great speeds!!!
I have to try the A700 out: It has two double cross center AF points and early owners seem to believe this camera is quite fast... even without their SSM



Here's with the EF 500 f/4 with 1.4x TC (@ 700mm): One-Shot AF, tracking will not work since the background is quite busy while the subject is way too small, beside the wings are beating so fast that the AF will never lock in AI-servo!

[eric s]

Nice hummingbird.

-> Theses guys have no predetermined fly path, but zig zag on a dime at great speeds!!!

I have to completely disagree with you there. You didn't shoot him flying around doing the zig-zag thing. You shot him in a predicatable place doing a predictable thing - feeding.

Now, if you had a shot of one just flying by, then I'd be impressed by your flight skills.

Instead I'm impressed at your choice of composition and skill in exposing the shot. You did a good job taking a common type of shot (hummingbird feeding) and made it different from the behind-the-bird angle. Nicely done.

About every other baseball (or smaller) sized bird I can think of does not behave like a feeding hummingbird.
Try picking a more interesting example - like a warbler, swallow, vireo.... or almost any other small bird. 99% of all shots of them are seated, taking off, or landing. Not just flying by. (Note, I'm not going to say 100% 'cause people get lucky. I've seen it. But it was just that - luck.)

Eric

[NHL]

Eric

Did you look through the link? This one is definetly not feeding...






eric s wrote:

About every other baseball (or smaller) sized bird I can think of does not behave like a feeding hummingbird.
Try picking a more interesting example - like a warbler, swallow, vireo.... or almost any other small bird. 99% of all shots of them are seated, taking off, or landing. Not just flying by. (Note, I'm not going to say 100% 'cause people get lucky. I've seen it. But it was just that - luck.)

Do theses examples qualify ?
http://forums.steves-digicams.com/fo...mp;forum_id=11

[eric s]

Killdeer are certainly larger than a baseball at 10.5 inches long! (I don't believe that was a plover, the only US shorebird that has two black bibs is a killdeer.) And they certainly fly in predictable patterns. They can dart around, but they will also fly very straight and direct. Lovely shot, BTW.

And a hovering humming bird is more a testimate to your skill in getting the camera on it (and AF speed of the camera and lens.) That isn't a statement about why you should have 51 AF points or... What was your point?

I state again. I did not say that shots of small birds in flight (smaller than a baseball) were impossible, did I? What are you trying to demonstrate by showing the pictures (other than that you're a great photographer, which I already knew. )

One-Shot AF, tracking will not work since the background is quite busy while the subject is way too small, beside the wings are beating so fast that the AF will never lock in AI-servo!

Why wouldn't AI-Servo work on this shot? (I'm just thinking about this, I'm not trying to discredit the statement.) Background complexity would make no difference in that shot if you got the AF point on to the bird. Now, if the bird slipped out from under the AF, then you would be screwed. Is that what you're trying to say?

And wing beat speed shouldn't make a difference if you were close enough. Ya, if the AF sensor was big enough to get the body *and* a wing on the side then you'd be in trouble. But that would mess up one-shot as well because both AF mods lock on the closes thing under the AF sensor - the wings. So if you were close enough to use One-shot, then the wings shouldn't have effected Servo either.

I don't see how One-Shot or Servo would work differently because of the wings. It would definitely mess you up if the bird slipped off the AF point.

I've heard varying opinions on One-shot vs AI Servo over the years. I've seen stunning pictures taken both ways. I guess I just don't see how it works for flight shots because it doesn't let you easily track the subject to get the best bird position (like head angle.) I guess you could manually focus or repeatedly release and 1/2 press the shutter... that seems very awkward to me but I guess it could work.

When I do flight shots I try to pick the subject up at some distance and track them to the position I want and then start shooting when they are close enough and are properly posed. If the bird moves fast, your chance of success goes up dramatically if you can track them in (especially if you're using a big lens like I am. Combine a small field of view and the relativeistic speed different at closer distances and it's really hard to pick them up.)

Eric

[NHL]

eric s wrote:

Why wouldn't AI-Servo work on this shot? (I'm just thinking about this, I'm not trying to discredit the statement.) Background complexity would make no difference in that shot if you got the AF point on to the bird. Now, if the bird slipped out from under the AF, then you would be screwed. Is that what you're trying to say?

Exactly!

In theory AI-servo should work; however in practice (remember in real-life nothing is frozen like a still picture to analyze) several factors occur simultaneously:
1st - The bird is not posing still for you to keep an AF affixed to one spot (the body only for example)
2nd - With the long Tele, especially @ 700mm, you can not hold the lens still (try to handhold your 600mm for example), not that easy hey?
3rd - Can you track (see below) if you can't see?

-> Given that the AF point will move away from the tiny subject (beside the pictures were already cropped so the subject appears larger and off the center AF point).
o One-shot AF focus and stop so if your AF point is off it just take another 1/2 press of the shutter to get it lock back on because the focusing error is small, and you only tell the camera to focus when you manage to get the AF point back on the subject!
o In AI-servo however you can't tell the autofocus to stop (you can let go of the shutter, but that counter-intuitive) so when the AF point slip off the subject it goes so far out in the background that it takes an eternity to get the AF back on - That is if you can still track the subject with an out of focus lens...
o This is where the problem lies - Check the DOF on thoses shots, the flowers at the beak is merely a fraction away and it's already out of focus! If the AF point slips in AI-servo to the other flowers in the background you no longer see the bird. How can you track where the subject is anymore... if you can't locate it?
In one-shot AF "I guess you could... repeatedly release and 1/2 press the shutter... that seems very awkward to me but I guess it could work." ankward yes but you can follow the bird's zig zag path. In AI-servo you usually have to take your eye off the viewfinder to locate the bird again because of the "Combine a small field of view and the relativeistic speed different at closer distances and it's really hard to pick them up."


There's a few things to clarify too:
1. AI-servo is predictive so the actual focus area do not have to line up with exactly what the AF point 'sees' before the shutter is released - It could be slighly front or back focus depending on what the camera predicts the subject trajectory is before the curtain is up - You can google around but AI-servo "misses" still object all the time because to the camera, any movement is displacement including that of the camera relative to a perfectly still and fix object - This is no different than a radar gun clocking a park car(or a wall) going 10-15MPH when a person moves his radar gun!
-> One-shot AF just removes this uncertainty that's all (i.e. the focus area align with the AF point)
2. The wings on the hummer do not flap only to the sides, but rotate around the whole bird so it's body is mostly hidden behind - A good example here is the spokes of a rotating bicycle wheel even though every spokes are on the same plane the AF will have problem locking on the moving spokes!
3. You also seems get hang-up on 'baseball' size birds, but in practice it's the relative size of the target to the area of the AF point that count for example a big blue heron can also be small if it's far enough. On the otherhand a small bird can be quite large if you can get really close and fill-up the whole frame for the AF points to work on - Or a super Teles like ours and work near focus (almost macro like :-))



Trust me like everybody I would like nothing better than to switch to AI-servo and let all the 45 points on my camera do the work (and I do that too) - Why sweat? However more often than not I have found that the "ankward" way with one-shot AF works better for me for moving subjects that are fraction of the size of "gorilla" with helmet
-> So even though I think the 51 AF point on the D300 is great, I also believe the double cross center AF point on the A700 shows a lot of potential depending on what you're shooting