Why can DSLR autofocus seem faster than mirrorless autofocus?
Asked 9/20/2017
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I’m trying to understand autofocus differences between mirrorless cameras and DSLRs. In general use, DSLRs are often described as having faster autofocus, while mirrorless cameras are sometimes said to be slower. Why is that? Is mirrorless autofocus actually less accurate, or is the main difference about speed and how the autofocus system works?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
8y ago
2 Answers
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There seems to be some confusion as to what you are asking. This answer takes under assumption that you mean to compare AF in mirrorless cameras with through-the-OVF autofocus of DSLRs. In Live-View, both types of cameras behave the same and could theoretically perform identically. They do not in practice because components and processing are not optimized with the same priorities.
Wrong. Mirrorless camera focus is even more accurate than DSLR autofocus. Contrast-Detect AF used in mirrorless cameras is handled by a feedback loop reading the sensor and adjusting the lens and so has no alignment issues. Unlike the autofocus system used in DSLRs, it cannot suffer from back or front focusing issues.
Phase-Detect AF used in DSLRs is generally faster since knows which direction it needs to adjust focus and does not need to hunt. Panasonic is trying to achieve similar results by using Depth-From-Defocus to determine the amount of adjustment need to autofocus using Contrast-Detect and close the gap. To some extent, they have managed. The difference between Contrast-Detect and Phase-Detect autofocus in terms of speed is now very small.
Both types of systems are equally sensitive. Top DSLRs and mirrorless cameras can autofocus now down to -4 EV which is very very dark.
Many manufacturers of mirrorless cameras now use on-sensor Phase-Detect. While they use the same principal as DSLR Phase-Detect AF, they have more limitations since these are built-into the sensor while DSLRs uses separate specialized units.
Being able to read the sensor while performing autofocus is a significant advantage for mirrorless cameras which can perform Face-Detect, Eye-Detect and other features which are impossible with the Phase-Detect units used by DSLRs, even though when Live-View is engaged, a DSLR behaves the same as a mirrorless and indeed can (but does not always) have the same features as a mirrorless.
Of course both camps are also fighting to improve their systems and we have more and more choice to balance feature, sensitivity, accuracy and speed than ever before.
Originally by user1620. Source · Licensed CC BY-SA 4.0
user1620
8y ago
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Generated from our catalog & community — verify before relying on it.
Mirrorless autofocus is not inherently less accurate than DSLR autofocus. In fact, sensor-based contrast-detect autofocus used by many mirrorless cameras can be very accurate because it measures focus directly on the imaging sensor, so it avoids DSLR-style front- or back-focus calibration errors.
The main traditional advantage of DSLRs is speed when using the optical viewfinder. Their dedicated phase-detect AF module can determine both how far and in which direction focus must move, so it can drive the lens quickly toward focus. Contrast-detect AF, common in earlier mirrorless cameras, uses a feedback process that checks image contrast on the sensor and adjusts focus iteratively, which is typically slower.
In live view, DSLRs and mirrorless cameras work more similarly because both rely on the imaging sensor. In theory they can perform similarly, though actual performance depends on how the camera’s hardware, software, and processing are optimized.
So the short version is: DSLRs have often been faster; mirrorless has often been more inherently accurate; and the exact result depends on the AF technology and implementation.
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AI8y ago
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