Measuring Autofocus Speed

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taxboy

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Whenever a new camera model in a range is launched usually one of the much vaunted benefits is improved autofocus speed. Looking at camera reviews I often read that the autofocus is much faster than its predecessor.
However is this a subjective statement (which may be correct)? or is there objective data to support this?
 
I think it's both. Some aspects of autofocus can be measured for specific camera body and lens combinations (CIPA wrote a spec for that). Personally, the reliability of continuous autofocus tracking matters more than single-frame speed, and I don't think there is a standardised testing methodology for it; reviewers each do their own thing, so it's best to try it hands-on if you can.
 
TimHughes said:
I think it's both. Some aspects of autofocus can be measured for specific camera body and lens combinations (CIPA wrote a spec for that). Personally, the reliability of continuous autofocus tracking matters more than single-frame speed, and I don't think there is a standardised testing methodology for it; reviewers each do their own thing, so it's best to try it hands-on if you can.
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I did wonder and as you say tracking autofocus is what most photographers want in the real world. I think it's probably like taking a more modern car for a test drive; most things feel better but only having purchased it and driven for a while do the quirks start to become noticeable
 
taxboy said:
Whenever a new camera model in a range is launched usually one of the much vaunted benefits is improved autofocus speed. Looking at camera reviews I often read that the autofocus is much faster than its predecessor.
However is this a subjective statement (which may be correct)? or is there objective data to support this?
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I often think it’s just a perception, with some of the modern mirrorless cameras AF lock on is near instant, I don’t know how much faster it can be than that. Focus speed between near and far subjects can be detected more, however I would hazard a guess this is more down to the lens motors than the camera body.

Where you can (imo) see a noticeable difference in AF is subject recognition and the ability to track without getting distracted by backgrounds. However, we are now reaching a point where this is getting pretty flawless too so, barring the odd ‘anomaly’ I’m not sure how much better this can get either. If we’re not too careful we’re going to end up with 50 different subjects we can choose from.
 
snerkler said:
If we’re not too careful we’re going to end up with 50 different subjects we can choose from.
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right..... canon R1 has three subject types (people, animals and vehicles), and people tracking can be further refined by four sports, and you can pre-load up to 10 specific faces to prioritize. it takes a while to configure and learn to use, but you have a good chance of filling a card with 100% usable frames.
 
TimHughes said:
right..... canon R1 has three subject types (people, animals and vehicles), and people tracking can be further refined by four sports, and you can pre-load up to 10 specific faces to prioritize. it takes a while to configure and learn to use, but you have a good chance of filling a card with 100% usable frames.
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On top of a plethera of focus modes (tracking, AF-C, AF-S etc etc) and focus areas (single point, wide, centre etc etc) my A1 II has the following subject detection:-

Auto
People (with face memory and face priority select)
Bird/Animal
Bird
Animal
Insect
Car/Train
Plane

You can then choose which eye, or whether that's auto. Then there's

Tracking Shift Rnage
Recognition priority set
Recognition part
Recognition part select
Tracking persistence level
Recognition sensitivity
Animal Detailed settings
Bird details settings

And if this isn't enough you have:-

AF Level for crossing
AF tracking for speed changes
AF transition speed (video)
AF subject shift sensitivity
AF area registration

There's probably a few more bits, but as you can see it's getting ridiculous. Of course some of the things are super handy, but if we continue along this path are we going to get other subject option sub menus such as:-

Birds > Small Birds > Large Birds > Birds of Prey etc. etc.

Obviously with the last bit I'm being a bit facetious but you get my point ;)

One subject that I would like that's missing is Motorcyle/Motorcyle rider, I do believe some other systems have this.
 
snerkler said:
On top of a plethera of focus modes (tracking, AF-C, AF-S etc etc) and focus areas (single point, wide, centre etc etc) my A1 II has the following subject detection:-

Auto
People (with face memory and face priority select)
Bird/Animal
Bird
Animal
Insect
Car/Train
Plane

You can then choose which eye, or whether that's auto. Then there's

Tracking Shift Rnage
Recognition priority set
Recognition part
Recognition part select
Tracking persistence level
Recognition sensitivity
Animal Detailed settings
Bird details settings

And if this isn't enough you have:-

AF Level for crossing
AF tracking for speed changes
AF transition speed (video)
AF subject shift sensitivity
AF area registration

There's probably a few more bits, but as you can see it's getting ridiculous. Of course some of the things are super handy, but if we continue along this path are we going to get other subject option sub menus such as:-

Birds > Small Birds > Large Birds > Birds of Prey etc. etc.

Obviously with the last bit I'm being a bit facetious but you get my point ;)

One subject that I would like that's missing is Motorcyle/Motorcyle rider, I do believe some other systems have this.
Click to expand...

by the tine all that is set up a guy in a car will be home with his feet up having a coffee :exit:
 
Autofocus speed is highly dependent on environment/scene and camera setup (there are CIPA guidelines for that), but also/equally/moreso upon the lens in use. If you have a lens of high IQ, with fast drive motor(s), and lightweight focus elements, then any differences in focus speed will most likely be "incremental" and difficult to discern/measure without highly technical testing/equipment.

IME a lot of it is "impressions", and to some extent wishful thinking/"glow." In general, there are "differences," but not that one is necessarily better overall or in all situations... E.g. there are plenty of times where I find mirrorless AF to be lacking compared to the DSLR's dedicated PDAF system.
 
sk66 said:
. there are plenty of times where I find mirrorless AF to be lacking compared to the DSLR's dedicated PDAF system.
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That’s interesting, I’ve got to say the mirrorless I’ve used have been streets ahead in all areas of AF for me, such as lock on speed, subject recognition, subject tracking etc. However, I did only shoot Nikon DSLR and I know they had a history of the AF being distracted by backgrounds. I remember someone on here with a D5 (I think it was) having plenty of discussions about this with Nikon to try and resolve the issue of it focussing on the background when the backgrounds were ‘busy’.
 
snerkler said:
However, I did only shoot Nikon DSLR and I know they had a history of the AF being distracted by backgrounds.
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I don't find my Z9 to be any better in this respect. I think perhaps with easier subjects the mirrorless AF AI (subject recognition, etc) performs "better"... but I didn't/don't really have significant issues with DSLR's in those scenarios either (although I really didn't like the D7000 I had for a while, so maybe model dependent).
 
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sk66 said:
I don't find my Z9 to be any better in this respect. I think perhaps with easier subjects the mirrorless AF AI (subject recognition, etc) performs "better"... but I didn't/don't really have significant issues with DSLR's in those scenarios either (although I really didn't like the D7000 I had for a while, so maybe model dependent).
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In my experience, it varies a lot by camera body. My Fuji GFX, for example, has comparatively poor AF performance vs, say, a Canon 1DXM2 DSLR. On the other hand, the Canon R1 is a big step up from the 1DXM2. I understand that mirrorless bodies can't detect the low-light assist beams emitted by flashes (and which were designed for DSLRs), but I have never found that to be a problem.
 
TimHughes said:
I understand that mirrorless bodies can't detect the low-light assist beams emitted by flashes (and which were designed for DSLRs), but I have never found that to be a problem.
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Yeah, it's not about the focus assist with speedlights. It's about the lack of cross type sensors, and the fact that the DSLR's PDAF system is working with multiple real images that are (almost) always in-focus (as many as six) so it can (often) find subjects in/through distractions much better.

With mirrorless the AF is using the same image you see (actually two virtual images), so if the subject is way OOF the AF system can't see it; and it is likely to blow right past it if it is not large in the viewfinder. And the AI requires time to kick in and for the AF to switch modes (into subject recognition/tracking); it won't do that if it already locked onto something else w/o the subject also being discernable/recognizable and within the designated area (locked onto BG/FG).

There are tricks to help get the most out of the mirrorless AF, and those tricks also work with DSLR's... it's just that mirrorless is more dependent on using them. Of course, less demanding scenarios make the differences less apparent and even put the mirrorless ahead.

I wouldn't necessarily say the DSLR is way ahead in all demanding situations either; just "different." And I am comparing top level bodies (D4, D5, Z9)...
 
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sk66 said:
Yeah, it's not about the focus assist with speedlights. It's about the lack of cross type sensors, and the fact that the DSLR's PDAF system is almost always working with multiple real images that are (almost) always in-focus (as many as six) so it can (often) find subjects in/through distractions much better.

With mirrorless the AF is using the same image you see (actually two virtual images), so if the subject is way OOF the AF system can't see it; and it is likely to blow right past it if it is not large in the viewfinder. And the AI requires time to kick in and for the AF to switch modes (into subject recognition/tracking); it won't do that if it already locked onto something else w/o the subject also being discernable/recognizable and within the designated area (locked onto BG/FG).

There are tricks to help get the most out of the mirrorless AF, and those tricks also work with DSLR's... it's just that mirrorless is more dependent on using them. Of course, less demanding scenarios make the differences less apparent and even put the mirrorless ahead.

I wouldn't necessarily say the DSLR is way ahead in all demanding situations either; just "different." And I am comparing top level bodies (D4, D5, Z9)...
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I know you know your stuff but I find this surprising, I've never seen this reported or mentioned in any comparison. I understand the pros of cross type sensors, but the pros of modern algorithms outweigh this.

That being said you've had first hand experience using these bodies so I'm not disputing your findings, I just find it surprising that's all (y)
 
snerkler said:
I understand the pros of cross type sensors, but the pros of modern algorithms outweigh this.
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The algorithm takes time to work.

I.e. using my Z9 with bird subject recognition active and in 3D focus mode (color/pattern recognition).
Initially it is in 3D focus mode and it will lock onto/track a point of color under the selected focus point (as advertised/described); and it doesn't care if it is a bird or not. After the initial focus acquisition it may detect that it is a bird, and then it may jump to the bird's eye; even if it is not the same area or color initially acquired. I.e. it abandons the 3D focus mode and switches into subject/eye tracking (it can't do both). But if not, it does not refuse to focus/function; it stays in 3D mode instead. I.e. it will focus on a human face, but it won't switch to subject recognition or track an eye.

And it behaves similarly in the other focus modes (wide area, etc). The easier the subject/situation is, the less time the algorithm needs; but it cannot even begin to function until the subject is already (very nearly) in focus in the viewfinder. It also needs a pretty decent image to work with (light/contrast/etc)... e.g. auto capture (subject recognition) is worthless for foxes at night (even at close range and side lit, I expected more). To be honest, I haven't entirely figured out what it needs; sometimes it seems to work pretty well with a dim image/viewfinder.

Obviously I can't speak about every camera make/model; over the years I've owned/used quite the variety and there are always differences. But the basic premise holds for all AI autofocus systems... it must first be able to see/discern the subject (focus), before it can then determine what kind of subject it is, and then (hopefully) find/track an eye. And the more deterministic (picky) the system is, the slower it will be (my Z9 will sometimes pick out a highlight on a leaf as being an eye, so not terribly picky).

If you pick a mode without subject recognition, or disable it, then the AF is basically handicapped compared to a DSLR (but it may benefit from faster processing, etc, of newer technology). Not that that is necessarily a problem either...(and a few mirrorless do have cross type points).
 
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sk66 said:
The algorithm takes time to work.

I.e. using my Z9 with bird subject recognition active and in 3D focus mode (color/pattern recognition).
Initially it is in 3D focus mode and it will lock onto/track a point of color under the selected focus point (as advertised/described); and it doesn't care if it is a bird or not. After the initial focus acquisition it may detect that it is a bird, and then it may jump to the bird's eye; even if it is not the same area or color initially acquired. I.e. it abandons the 3D focus mode and switches into subject/eye tracking (it can't do both). But if not, it does not refuse to focus/function; it stays in 3D mode instead. I.e. it will focus on a human face, but it won't switch to subject recognition or track an eye.

And it behaves similarly in the other focus modes (wide area, etc). The easier the subject/situation is, the less time the algorithm needs; but it cannot even begin to function until the subject is already (very nearly) in focus in the viewfinder. It also needs a pretty decent image to work with (light/contrast/etc)... e.g. auto capture (subject recognition) is worthless for foxes at night (even at close range and side lit, I expected more). To be honest, I haven't entirely figured out what it needs; sometimes it seems to work pretty well with a dim image/viewfinder.

Obviously I can't speak about every camera make/model; over the years I've owned/used quite the variety and there are always differences. But the basic premise holds for all AI autofocus systems... it must first be able to see/discern the subject (focus), before it can then determine what kind of subject it is, and then (hopefully) find/track an eye. And the more deterministic (picky) the system is, the slower it will be (my Z9 will sometimes pick out a highlight on a leaf as being an eye, so not terribly picky).

If you pick a mode without subject recognition, or disable it, then the AF is basically handicapped compared to a DSLR (but it may benefit from faster processing, etc, of newer technology). Not that that is necessarily a problem either...(and a few mirrorless do have cross type points).
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My experience with the A1 and A1 II is somewhat different tbh, it’s almost telepathic.

Of course if you have it in subject detect mode and you’re not shooting that subject so it’s not in the frame it will still try and detect that subject, which on occasion can trip it up, but that’s user error imo and not a ‘fault’ of the AF.

Obviously in such situations it’s better to turn off subject recognition , but even then I’ve found every aspect of AF better than the DSLRs I’ve owned. Even the examples you’ve mentioned, i.e. when the subject is initially completely OOF. Of course there’s so many variables to this that it makes sense we can all have different experiences (y)
 
I had Canon DSLR's, 300D, 10D, 20D and 5D. Admittedly maybe not earth shattering technology there. Every mirrorless camera I've had apart from the Fuji's has been in a different league, a better one. I remember reading on the Canon website that if you took 3 pictures you'd see focus differences between them and this was normal. I don't think I care how fast a focus system like that is if it's that inconsistent plus there was that whole Micro Adjust fiasco and differences between bodies and lenses. Nightmare. Give me mirrorless every time :D
 
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