How can autofocus performance be measured, and how much do the lens and body each matter?
Asked 11/23/2011
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Lens reviews often describe autofocus subjectively as fast, slow, or prone to hunting. Since autofocus also depends on the camera body, AF system, and lighting, I’m wondering whether lens AF performance can be measured in a more objective way if those variables are kept constant. For example, using the same camera body and standardized lighting, is there a meaningful way to quantify autofocus speed or tracking performance? Also, in practice, which has more influence on autofocus performance: the lens or the camera body?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
14y ago
2 Answers
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Speed
The best value to compare the autofocus speed is to know how long it takes (attached to your camera body) to move the focus lens from the minimum position to the maximum position.
Detection
The most difficult part of comparison is to measure the autofocus-detection-speed. This strongly depends on the camera body you use, so you need to try it or find a review about it.
Before buying
Before buying (or even comparing) an autofocus lens, you should think about it in greater detail. For most photography (according to my experience) you do not really need a very fast autofocus, so the question of speed defeats its purpose. Even if you want to do sports or wildlife photography where you need really fast autofocus, you should be satisfied with nearly every lens that has a silent-wave motor.
Also, on this note, which influences the AF ability of a camera more - the lens or the body
This strongly depends on the lens you want to use, some are slowed down by the camera body and some are slower than the body could be.
Originally by user1297. Source · Licensed CC BY-SA 4.0
user1297
14y ago
0
Generated from our catalog & community — verify before relying on it.
Yes—if you keep the body and lighting constant, the most objective lens-related AF metric is focus travel time: how long the lens takes to move from minimum focus distance to infinity (or the reverse) on the same camera body. That gives a comparable measure of focus-drive speed.
What’s harder to isolate is autofocus detection and tracking performance. Those depend heavily on the camera body’s AF system, so any test of acquisition speed, hunting, or AF-servo/tracking is really measuring the lens-and-body combination, not just the lens alone.
In other words:
- Lens influence: how quickly and smoothly the lens can physically move its focusing elements.
- Body influence: how quickly and accurately the camera detects focus and controls the lens, especially in low light or continuous AF.
So the body usually has a major effect on whether AF locks, hunts, or tracks well, while the lens affects how fast the commanded focus change can happen. For practical buying decisions, the best comparison is the exact lens on the exact camera body you plan to use.
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AI14y ago
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