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10-18-2015, 12:30 PM   #1
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So why is mirrorless autofocus not up there with dslrs?

Many pros out there are being cautioned against switching to mirrorless for the af (from what ive been its perfectly fine for weddings) so i wanted to ask is there any certain reason why mirrorless ends up comming up behind dslrs for af? One has on sensor autofocus and the other one bounces light into an af module. Not the most technically astute of explainations but its essentially true. Correct me if im wrong. From the point of someone is not very well shall we say technically informed, it seems like the mirror less would actually be faster? The samsung nx1 has a 6.5k sensor that it downscales in real time to 4k. It makes your average nikon dslr with its 1080/30p look like one of the original smartphones


10-18-2015, 12:46 PM   #2
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I think its just because contrast detect focusing needs to move the focus mechanism, then check the focus to see if contrast is optimized, and so on. And then when it overshoots, it has to go back.
While PD AF just looks at two wavelengths and can probably even use lens profiles to predict where focus most likely is. PD AF has also been around for a very long time, so it highly optimized and has its own AF modules; while CD AF is a rather new thing and uses CPU (which may or may not be super fast)

Phones are different because it uses much smaller sensors with relatively low aperture, so DoF is big, hyperfocal and pan focusing are not difficult. All of this really helps mask any kind of AF errors and makes AF easier (only need to move a little bit of glass a small distance)
10-18-2015, 02:18 PM   #3
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My LG G3 improved focus by adding a laser.

Hybrid pdaf / cdaf on sensor focus is relatively new innovation and still lags PDAF in speed.
10-18-2015, 03:25 PM   #4
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The problem is with auto focus guessing which direction to move to move. CD AF has to move make an assessment and then continue or back track. PD AF on the sensor on the highest end cameras works quite well, however. I don't know that it is quite as good at low light focus as an SLRs auto focus -- probably depends. Tracking also has been a little more problematic on mirrorless cameras as well.

If your interest is in video, then mirrorless is fine. Most videographers don't use auto focus for video anyway.

10-18-2015, 06:00 PM   #5
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my phone lens goes infinity after less than 2ft... there is a setting to lock infinity which i use because 99% of my photos are past it and it speeds up shots.
10-18-2015, 08:11 PM   #6
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I have a friend that's a pro. He switched from Canon full frame to Panasonic GH4. Says AF is just as good.

My Nikon 1V1 AF is better than my K-3.
10-18-2015, 08:33 PM   #7
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Mirrorless AF is more dependent on processing power and how many times per second can the sensor be read and AF updated. If the sensor is only capable of reading 5 fps, then AF tracking is going to be awful. We are just now seeing sensors that can be read fast enough, but the processing power is killing batteries in mirrorless bodies. Then there is the issue of lenses designed for CDAF vs PDAF and the size of the focusing elements. Smaller formats have an advantage because is easier to move smaller groups. M4/3 has a very quick lenses. We are starting to see a huge increase in processing power. The Samsung NX-1 was the first and Sony followed. This is where 4K video at 60fps is going to help still photographers. As the camera manufactures are pushing for better video specification they are creating better still cameras. If your camera AF can read the sensor AF points at 60fps, then it will have amazing AF tracking. This is one reason why the GH-4 has such great AF.

For mirrorless cameras its about processing power and how fast the sensor can refresh. Combining PDAF and CDAF on sensor adds to the processor load but has a lot of advantage. More processing power, more battery power, faster sensors..

10-19-2015, 05:39 AM   #8
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That said, I quite enjoy the K-01, its AF is fast enough for pretty much all my uses, it works well with MF, and it has a good battery life. So this difference in AF speed is not something that everyone must care about. But it can be important for some types of photography
10-19-2015, 03:49 PM   #9
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QuoteOriginally posted by Na Horuk Quote
That said, I quite enjoy the K-01, its AF is fast enough for pretty much all my uses, it works well with MF, and it has a good battery life. So this difference in AF speed is not something that everyone must care about. But it can be important for some types of photography
How about AF accuracy - is that important? In general, mirrorless AF is more accurate than DSLRs in that it doesn't require all those lens tests by the owner to micro adjust the camera to the lenses. Each mirrorless AF operation is essentially a calibration test because it adjusts to the image on the sensor itself. Since zoom lenses can have an infinite number of focal lengths, calibrating phase focus adjustments on a zoom lens was always an approximation.
10-19-2015, 04:00 PM   #10
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QuoteOriginally posted by philbaum Quote
How about AF accuracy - is that important? In general, mirrorless AF is more accurate than DSLRs in that it doesn't require all those lens tests by the owner to micro adjust the camera to the lenses. Each mirrorless AF operation is essentially a calibration test because it adjusts to the image on the sensor itself. Since zoom lenses can have an infinite number of focal lengths, calibrating phase focus adjustments on a zoom lens was always an approximation.
With CDAF that should be true - not sure if PDAF is subject to calibration on sensor or not. Remember that PDAF is now making inroads on the sensors.
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