Factors that affect speed of AF

[Colin Southern]

One reason to love the new generation Canon lens. VR/IS does not kick in at all and only does when the shutter button is fully depressed. Have not seen that to have any adverse affect on sharpness. The older modes 1 and 2 are still there if needed.

I didn't know that. My latest IS lens is the EF 70-200mm F2.8L IS USM II - and that starts IS when I 1/2 press the release.

Are you sure you haven't just disassociated focusing from the release button?

[Bobobird]

They call that Mode 3 which only activates at the point of exposure.

I use the back button so IS has always been disassociated from release.

[Colin Southern]

They call that Mode 3 which only activates at the point of exposure.

I use the back button so IS has always been disassociated from release.

Ah - OK. Thanks for that.

[t6b9p]

Dan I think we are coming at this from different angles

My point earlier. VR is slow. Has nothing to do with AF. The AF is doing its thing a lot faster than the VR.

I do think one effect that VR has on AF has nothing to do with speed. With VR on, the image floats around a bit. So you can't hold the AF point exactly where you want it. .............
..... I shoot with VR off at high ss. It's simple logic. Why throw another variable into the equations when it's not doing any good anyway. It takes VR so long to settle down in the first place, I can't figure out what it's doing in the 1/10 of a second between frames

We agree that VR is slow and that VR is a separate function from AF. If you lock on fast with AF and then you activate VR it delays image capture by that annoying "1/10s".

So you can't hold the AF point exactly where you want it

Not a problem for static or large moving subjects however small fast moving subjects can be difficult to track with AF at the best of times, throw in a 1/10s delay and your subject has moved 7ft at 50mph. Shooting 300/2.8 at f/5.6 with a subject at 30ft gives a DOF under 1ft - with VR on you will probably lose focus while it is "making up its mind". So now any advantage of fast AF has been lost. While this does not directly affect the speed of AF, it negates having fast AF in the first place and in that respect, VR indirectly effects AF speed by degrading its performance.
The OP asked

What factors influence how fast AF focuses?

So my response is for fast moving subjects, VR is a degrading factor in how fast AF focuses.

[RustBeltRaw]

None of my current lenses have IS, though a couple relatively old ones I've sold did. I haven't missed it, really, and I usually kept it turned off unless I was more or less pure left-to-right panning. Since a vast majority of Canon's IS use instructions regard panning cases, that implies that most of the design effort was aimed at that.

For subjects approaching or leading the camera, shutter lag becomes important, so if IS does increase shutter lag, giving the subject more time to leave the focal plane, it makes sense to turn it off.

[NorthernFocus]

Dan I think we are coming at this from different angles


We agree that VR is slow and that VR is a separate function from AF. If you lock on fast with AF and then you activate VR it delays image capture by that annoying "1/10s".
Not a problem for static or large moving subjects however small fast moving subjects can be difficult to track with AF at the best of times, throw in a 1/10s delay and your subject has moved 7ft at 50mph. Shooting 300/2.8 at f/5.6 with a subject at 30ft gives a DOF under 1ft - with VR on you will probably lose focus while it is "making up its mind". So now any advantage of fast AF has been lost. While this does not directly affect the speed of AF, it negates having fast AF in the first place and in that respect, VR indirectly effects AF speed by degrading its performance.
The OP asked
So my response is for fast moving subjects, VR is a degrading factor in how fast AF focuses.

As much as I hate to stay on this merry-go-round, there are a lot of newbies who read these posts and I hate to think they get erroneous or confusing info. I hope what you wrote doesn't reflect what you were attempting to say. So why don't you re-read and edit it and save me a lengthy response

[t6b9p]

I'm already off the merry-go-round.

[PhotomanJohn]

Someone is confused. On my D7000, the shutter activates immediately when the button is pushed whether on not VR has even started to engage. My understanding is that focus is the only priority before the shutter will release on most cameras. I have that disabled so it goes when I say go.

John

[NorthernFocus]

Someone is confused. On my D7000, the shutter activates immediately when the button is pushed whether on not VR has even started to engage...John

Exactly so, John.

...We agree that VR is slow and that VR is a separate function from AF.

And yet...

If you lock on fast with AF and then you activate VR it delays image capture by that annoying "1/10s".

That's not only contradictory, but I'm not sure how you get a lock with AF and then activate VR. At least on Nikon gear. If I'm missing a function I would much appreciate sharing how this is accomplished. But on all of the Nikon gear that I've had the opportunity to use, VR activates when either the shutter or AF-ON button are depressed. So if one is utilizing BBF, it is possible to activate VR without AF, but not vice versa.

Not a problem for static or large moving subjects however small fast moving subjects can be difficult to track with AF at the best of times, throw in a 1/10s delay and your subject has moved 7ft at 50mph.

I'm still confused as to where the delay is coming from if we're agreed that AF and VR function independently of one another

... with VR on you will probably lose focus while it is "making up its mind".So now any advantage of fast AF has been lost. While this does not directly affect the speed of AF, it negates having fast AF in the first place and in that respect, VR indirectly effects AF speed by degrading its performance.

OOOOOK. Let's see if I'm following this. AF locks on, THEN VR is somehow engaged. But while VR is working, AF apparently stops functioning, then AF re-engages but it's too late to do any good. Well now I'm really confused. Rather than VR and AF being independent functions, this sounds like a mutually exclusive dependency.

So my response is for fast moving subjects, VR is a degrading factor in how fast AF focuses.

Confidently stated, clearly believed, and no doubt well intended. But this statement has no basis in fact.

[PhotomanJohn]

That's not only contradictory, but I'm not sure how you get a lock with AF and then activate VR. At least on Nikon gear.

Dan - I think this was mentioned in a thread awhile back but not all Nikons work exactly the same. In the case of the D7000 when you use the AE-L/AF-L button (since it doesn't have an AF-ON button) for BBF it doesn't activate the VR, only the focus. If I want the VR on while focusing I have to also press the shutter half way. I think that someone said the D7100 was not that way but I don't remember for sure.

John

[PhotomanJohn]

Thinking about it a little more I remembered that Nikon's VR system re-centers itself just before the exposure to allow to the maximum compensation in any direction during the exposure. The following is from the Nikon site.

"Nikon’s VR System changes operation algorithms when the shutter release button is lightly pressed and during exposure. Therefore, when the shutter release button is lightly pressed, the VR lens gives you a smooth viewfinder image. During the exposure, however, the algorithm changes to compensate for every slight movement. What’s more, just before exposure, the VR lens will reset to central position (optical axis) from an off-centered position which is a result of VR operation during the shutter release button is lightly pressed. Since the shift amount of the VR lens is limited, this operation maximizes VR effects as well as optical performance. Only Nikon has this "Centering Before Exposure" feature."

This would add some delay unless it is completed during the time the mirror is flipping up which I believe is the case??

John

[NorthernFocus]

Thinking about it a little more I remembered that Nikon's VR system re-centers itself just before the exposure to allow to the maximum compensation in any direction during the exposure....
This would add some delay unless it is completed during the time the mirror is flipping up which I believe is the case??

John

John, AF is still not defeated while VR is doing all of this, so, with regard to AF SPEED, it has no effect. HOWEVER, this is one of the things that I alluded to earlier about VR making the image move around and affecting the focus point. Though I've never seen it clearly stated, I believe for action type photography this is the issue that "degrades image quality" with VR turned on. It's hard enough to keep focus point on moving targets. Harder yet with the VR moving lens elements around too. So best to just turn VR off in those situations.

You know it's really amazing when you think about it. I typically shoot 10 fps when shooting BIF. So in 1/10s, the mirror flips up, shutter fires, mirror flips back down, AF adjusts, VR adjusts, and the cycle starts again. Cool, huh?

Oh and thanks for the point about the D7000. I only started using BBF with the current generation of bodies. I had a 7000 but didn't BBF at the time plus didn't use it for BIF anyway as the AF wasn't up to the task. Also on all previous bodies I used shutter button focus. I wish they'd go back to that. It is really aggravating having VR activate when you just want to check focus

[Brownbear]

Thank you for starting this thread...

So if one places an extender on their lens this reduces light and focusing speed?

And low light is why it is harder to focus on birds in flight in the fog (or just low light)? And low contrast might be why it is sometimes challenging to focus on a a single heron just floating on water (nothing else in the scene trying to grab focus) ?

[NorthernFocus]

Christina, AF is really mostly about contrast. There are other directional nuances when not using one of the "cross sensors", but contrast is the main factor. Low light, fog, smaller apertures all equate to less contrast available at the focus sensor. Assuming you're using AF-S lenses, the only effect of an extender is that they cut down light/decrease max aperture. So anything that reduces contrast negatively impacts AF speed/accuracy.

[Brownbear]

Thank you Dan..

Why is it that sometimes one can focus on a bird in a tree amongst a zillion branches, using either auto focus or manual focus... But that it is sometimes seemingly impossible to grab focus on a solitary bird on water using either auto focus or manual focus.. ie; even with manual focus the camera seems unable to grab focus? The latter doesn't make any sense to me, ie; it should be harder to grab focus on a bird sitting behind a bunch of branches.

Thank you.

Christina, AF is really mostly about contrast. There are other directional nuances when not using one of the "cross sensors", but contrast is the main factor. Low light, fog, smaller apertures all equate to less contrast available at the focus sensor. Assuming you're using AF-S lenses, the only effect of an extender is that they cut down light/decrease max aperture. So anything that reduces contrast negatively impacts AF speed/accuracy.

[PhotomanJohn]

Thank you Dan..

Why is it that sometimes one can focus on a bird in a tree amongst a zillion branches, using either auto focus or manual focus... But that it is sometimes seemingly impossible to grab focus on a solitary bird on water using either auto focus or manual focus..

Chritina,

I am not sure if you are using single or multiple focus points in these situations but in both these cases I would be using the center point only. I would be very surprised if you place the center of the focus point on an edge of the bird that it would not focus properly. As far as in manual focus, it is difficult to manually focus on a small object if that is the case with the bird on the water. When the bird is in the tree, you have the branches to help you home in on the proper focus.

John

[NorthernFocus]

Were you using the same focus mode in each situation? Same focus point selected? If you are using a single focus point (S as opposed to d9, d21, etc.) and one of the nine points in the middle, then it's simply what you've place that point on. If the focus point is on the bird's head then the branches are irrelevant. Same thing with the bird on the water, if the focus point is on the bird, then you should be good.

But if you are using multipoint focus modes, then squirrely things can happen. And the squirreliness is compounded by low contrast situations. Multipoint is designed for helping track moving objects. Definitely when shooting static subjects I recommend single point if you want to be assured of nailing critical focus.

[Bobobird]

Hey Dan - Just Af'd on something, low contrast etc but focus locked after a bit.

Confusius <> Confucius
I know gunpowder, paper, etc were invented in China. Photography too?

[Brownbear]

Thank you John and Dan for your helpful replies.

I was using single point auto focus...

Foggy morning, low light.

Worked well for an eagle sitting and landing in a tree. Yes, focusing on the birds head so that is good to know.

The image that gave me trouble was a heron on water. At first I tried a single point on far right side, and reverted to trying center point focus when I couldn't grab focus... Even harder in a vertical composition. I suppose the image is in focus but not sharp, and it was so hard to do... Ie; my camera just kept refusing to grab focus or keep the focus. Perhaps with more practice...

Thank you.

[PhotomanJohn]

Christina,

Are you using single or continuous focus mode? If you were in continuous maybe there was enough camera motion such that the focus point was falling off the subject then back on causing the camera to change the focus. If you were able to see it going in and out of focus you might try (if not already) using back button focus set to AF-C and disable the shutter button from focusing. This way you can play with the auto-focus until it looks right then stop focusing and take the shot.

John