Can the Autofocus performance of a lens be quantified?

For the purpose of comparing attributes of different lenses, I want to know if there are standards used to measure or quantify the speed of acquiring focus or the time it takes to acquire focus.

I've read many formal and informal lens reviews and AF performance is often mentioned, but the point tends to be subjective. Take two of my lenses, for example: the EF-S 17-55 f/2.8 is often described as one of Canon's fastest lenses, with regard to AF performance, but, when describing my EF-S 60 macro, the word "hunts" is often used. Based on personal experience, I completely agree with those assessments of these lenses; but are there any standards by which to compare in order to quantify that?

A quick search on goggle yielded little insight. One post (on another forum) suggested that simply measuring the time it takes for the motor to move the elements from the shortest focus distance to ∞ should be used because anything else is too subjective. And while I understand the point, there are many variables to muddy a study, body for example: I would expect most lenses to perform better, in the field, while on a 5DIII than a 6D, but not necessarily in a studio. It seems that some controlled tests could be (should have been) devised by which the AF performance of a lens can be quantified for comparison purposes.

BTW: what got me thinking about this: there is a person who posted because he is considering the worthiness of upgrading his older 70-200 f/2.8L (non IS) to the 70-200 f/2.8L II. I was trying to come up with the benefits of such an upgrade. I believe that AF on the newer lens is faster, but I don't know that for sure, and don't know where to turn for data that would either confirm or disprove that belief that have: does it exist?

hairy_moth wrote in post #16542053
For the purpose of comparing attributes of different lenses, I want to know if there are standards used to measure or quantify the speed of acquiring focus or the time it takes to acquire focus.

I've read many formal and informal lens reviews and AF performance is often mentioned, but the point tends to be subjective. Take two of my lenses, for example: the EF-S 17-55 f/2.8 is often described as one of Canon's fastest lenses, with regard to AF performance, but, when describing my EF-S 60 macro, the word "hunts" is often used. Based on personal experience, I completely agree with those assessments of these lenses; but are there any standards by which to compare in order to quantify that?

A quick search on goggle yielded little insight. One post (on another forum) suggested that simply measuring the time it takes for the motor to move the elements from the shortest focus distance to ∞ should be used because anything else is to subjective. And while I understand the point, there are many variables to muddy a study, body for example: I would expect most lenses to perform better, in the field, while on a 5DIII than a 6D, but not necessarily in a studio. It seems that some controlled tests could be (should have been) devised by which the AF performance of a lens can be quantified for comparison purposes.

BTW: what got me thinking about this: there is a person who posted because he is considering the worthiness of upgrading his older 70-200 f/2.8L (non IS) to the 70-200 f/2.8L II. I was trying to come up with the benefits of such an upgrade. I believe that AF on the newer lens is faster, but I don't know that for sure, and don't know where to turn for data that would either confirm or disprove that belief that have: does it exist?

Unfortunately, autofocus performance has to be considered as a combination of a lens and a body. Even under those conditions, there are no standard tests.

Since each photographer is going to have different demands, there's no good way to judge autofocus performance except when the lens and camera are put to use in the intended task.

Some photographers want constant tracking of the nearest subject, and others want a camera and lens to guess the best settings when a subject is moving through a crowded frame.

It's easy to test a camera using a static optical bench and a chart, but when subjects are rapidly and unpredictably moving, there never will be a "standard." If you've ever photographed at a football field or a basketball court or tried to track a rapidly approaching subject, you can understand the challenges.

It's subjective. After time with any equipment you can feel if it's working the way you want, but that may be different from what someone else wants. That's why the more sophisticated camera autofocus systems have so many user adjustments.

It would be quite easy to measure the AF performance of any particular lens. The two quantities to measure are: time (ms) from pressing the button to acquiring focus, and accuracy (mm), how close the point of focus to the desired target. To be sure, the entire exercise would be quite pointless. It would only be meaningful when comparing two copies of the same lens, under EXACTLY the same conditions. The number of variables is huge, and quite uncontrollable: camera body, drive mode, focus mode, selected aperture, amount of light, temperature of light, color of subject, contrast at the AF point, and so on.

I have lenses that I can use indoors with any AF point on my 60D and they just work. Put that same lens on a 5Dc, use an outer point, and it hunts in broad-daylight.

I don't know of a standard test, and while one could be developed (and I'm sure Canon and Nikon have internal metrics for this), it's hard to write on to paper. Simply saying speed from min focus distance to max isn't a good measure. A macro lens has a much further range to cover, a f/1.2 needs to be much more accurate. The body the lens is attached to can affect the performance as well.

http://www.imaging-resource.com …ity-part-3b-canon-cameras

EOS5DC wrote in post #16542105
It would be quite easy to measure the AF performance of any particular lens. The two quantities to measure are: time (ms) from pressing the button to acquiring focus, and accuracy (mm), how close the point of focus to the desired target. To be sure, the entire exercise would be quite pointless. It would only be meaningful when comparing two copies of the same lens, under EXACTLY the same conditions. The number of variables is huge, and quite uncontrollable: camera body, drive mode, focus mode, selected aperture, amount of light, temperature of light, color of subject, contrast at the AF point, and so on.

I have lenses that I can use indoors with any AF point on my 60D and they just work. Put that same lens on a 5Dc, use an outer point, and it hunts in broad-daylight.

Bingo! We have a winner... if by "and so on" we include the photographer's skill level and practices, speed of subject movement (if any), direction of movement (if any), whether or not the ideal focus mode and focus parameters are being employed, what and how focus-related Custom Functions have been set (if available), whether or not Micro Focus Adjustment is available and in use (correctly).... and so on.

Popular Photography Magazine used to do a basic lab test of camera bodies, just sheer speed of acquisition under different light levels. Dunno if they still do, but there is so much more to it than that. It was just a point of comparison. AF performance is always going to be somewhat subjective.

Wrong, for manual focus lenses it can be measured pretty easy without considering the body or the task.

Sorry just had to :P

Static af performance should be pretty easy to quantify. In fact I believ lensrentals or someone did just that but only to illustrate differences across body models. As to why it's not done for all lenses I do not know. Maybe too time consuming.

However.... In my experience af accuracy (as opposed to speed) though varied greatly relative to other lenses matters faaaaaar less than just having a lens calibrated well or used with a body that is compatible with its calibration. I don't miss significantly more shots with a less precise lens but I do miss tons of shots cause a lens likes to switch between 0 and +7 ma randomly such as my 50 1.2.

Thanks for the feedback. The links were especially good reads.

ed rader wrote in post #16542366
http://www.imaging-resource.com …ity-part-3b-canon-cameras

Good read ed, thanks. It certainly answers my question of why I get more keepers with my 5d3, as compared to my 7d, with certain lenses.

Colt4570 wrote in post #16551270
Good read ed, thanks. It certainly answers my question of why I get more keepers with my 5d3, as compared to my 7d, with certain lenses.

Still using my 7D as my primary, but with a 5DIII on my shopping list; I'm still trying to figure out of that was good news or disappointing.

I was surprised to see how poorly they ranked the 7D, it was always been know for its feature rich AF system.

Colt4570 wrote in post #16551270
Good read ed, thanks. It certainly answers my question of why I get more keepers with my 5d3, as compared to my 7d, with certain lenses.

thanks. 5d3 + 24-70L II + auto iso = who needs IS ? most fantastic lens/camera combination I have used. easily.