AF on Mirrorless cameras

[Harlequin565]

I've been shooting film pretty much exclusively for the last 5 years. My digital camera is a Fuji X-T2.

On Monday I went to a wedding and took a film body with the Canon EF 50mm f/1.8 & 40mm f/2.8 as well as the X-T2 with the 50-140 f/2.8, 18-135 and the 35 f/1.4.

One glaring issue I had was that the X-T2 was positively sluggish in AF response (on all lenses - I know the 35 f/1.4 is not renowned for speed) and I missed a lot of focus, or the moment had passed by the time the camera had decided to take the picture. Picking out people in crowds meant the AF just went where it felt like. Conversely with the EOS30 (eye controlled AF off) and the 2 film lenses, I had a surprisingly superior hit rate. In good light, it was less of a problem, but in low light (at f/2.8 on the zoom and f/2 on the 35) it was dreadful compared to the EF 50mm at f/1.8-2.8

Is this (what I would call) poor AF performance "because it's a Fuji", or "because it's an older camera", or is it something more fundamental in EVF/Mirrorless cameras? If the latter - are there any mirrorless bodies out there that have cured this issue?

Don't get me wrong, I love the X-T2, but the vast majority of my photography has generally been stuff that sits relatively still, where slow/inaccurate AF isn't such an issue. I probably wouldn't have noticed if not for the wedding and my style of documentary photography - especially when it's the evening and everyone is having the most fun.

 

[woof woof]

I have a Sony A7 which is anything from reasonably fast to focus to rather leisurely depending on the lens so I'd say that the lens does make a difference. Things also slow down in lower light. I also have Panasonic MFT cameras and with most of my lenses they're blisteringly fast and still fast in low light. With some lenses you don't need to wait for any confirmation bleep you just point the camera and mash the shutter, the Panasonic 20mm f1.7 is a slug though.

So I'd say both the body and the lens matter.

 

[TCR4x4]

The xt2 isn’t very fast. The xt3 is slightly faster.
However I now have a Sony a9 and it’s faster than pretty much anything. You can shoot 20fps with a spaniel running towards you at full chat and every shot will be in focus.

 

[cambsno]

I have an XT3 after shooting 10years + with Nikon DSLR. The D750 for example was very fast and accurate. But I find that while i will get more OOF than I used to its not that much. Maybe if my hit rate before was 95% its now still above 90%

 

[sk66]

There are a number of very significant differences in how mirrorless on-sensor PDAF works in comparison to a DSLR's dedicated PDAF sensor/module. Some of the differences are:

It is very dependent on lens aperture for both low light effectiveness (f/1.x rated) and for Depth of Focus (ease of acquisition).
It is using a color filtered sensor which discards ~ 60% of available light (see above for low light).
It autofocuses at the selected aperture up to ~ f/8 typically, for increased Depth of Focus and exposure preview (at the expense of light).
The autofocus system sees what you see (a DSLR does not)... if what you see is dim/low contrast/significantly out of focus it will have more of an issue.
The mirrorless PDAF is functionally the same as a split prism viewfinder, a DSLR's PDAF module is quite different (although the very basis is the same).
And there are more possible issues/differences...

To compensate for all of these shortcomings the mirrorless PDAF function is typically operating in some form of fully Auto Mode (i.e. face detection, eye tracking, etc)... the newer, smarter, and more advanced those Auto algorithms are, the better the AF will be.

 

[the black fox]

I have a Olympus omd1-mkiii usually used with a 100-400 with or without t.c , it’s virtually instant AF , and used with a fast lens unreal focus speed

 

[Winslowe]

... the moment had passed by the time the camera had decided to take the picture. Picking out people in crowds meant the AF just went where it felt like.

We know the camera performs poorly when left to it's own devices - it would be interesting to know how it does with a photographer behind the controls.

 

[ukaskew]

I've shot weddings on mirrorless cameras for about 5 years now and haven't had any particular AF concerns, I started with the X-T2 interestingly enough! I used a D750 before that, whilst the X-T2 AF was slower it was certainly more accurate.

The 35mm 1.4 is pretty slow, most Fuji wedding shooters (and there are many) seem to use the 23mm 1.4 and 56mm 1.2, or the f2 versions which are substantially quicker.

I then moved to the Sony a7III which had/has the fastest and most accurate AF on any system I've ever used, Eye AF was a genuine game changer, I understand the latest Canon R bodies are exceptional too.

 

[nandbytes]

From what I know of Fuji their AF only really improved and caught up with other mirrorless systems from mk3 generation. Even then it's not fully caught up.

Also the older Fuji lenses like 35/1.4 or 56/1.2 are rather slow focussing lenses. I borrowed both and while I liked the image quality the AF was painful in comparison to what i had on other systems including older Minolta screw driven lenses.

Perhaps a body upgrade with careful lenses choices will help resolve your issue but it's certainly not a mirrorless wide issue.

 

[Gadget-Guy]

Have now had Fuji, Sony and Canon mirrorless cameras and a few 1 series canon bodies but the A/F on the little R6 i have seems to out perform them all and even the eye A/F of the Sony.

 

[robj20]

I've had the A7R and now the A7C which currently has Sony's best AF system and it often feels like cheating at times it's so good. I use AF-C the majority of the time now.

 

[the black fox]

money where mouth is time ,subject peregrine falcon the fastest bird in the world . camera olympus omd1-mkiii ,lens a old four thirds 18-180 (10 years old model) totally no problem locking on to this , and several other shots in the same burst all in focus .
done playing by jeff and jan cohen, on Flickr

 

[Nod]

Updating the firmware in the body and all the lenses can speed things up a bit.

 

[tijuana taxi]

Panasonic G9 is very fast acquiring focus

 

[Nod]

money where mouth is time ,subject peregrine falcon the fastest bird in the world . camera olympus omd1-mkiii ,lens a old four thirds 18-180 (10 years old model) totally no problem locking on to this , and several other shots in the same burst all in focus .

Not a particularly challenging scenario - the bird's flying flat and level, parallel to the plane of focus, not to mention being at relatively slow speed.

 

[dancook]

Sony A1 arguably the best/fastest AF a camera can offer and it’s mirrorless.

So no not an inherent thing with mirrorless, maybe perhaps early mirrorless.

 

[LCPete]

There are a number of very significant differences in how mirrorless on-sensor PDAF works in comparison to a DSLR's dedicated PDAF sensor/module. Some of the differences are:

It is very dependent on lens aperture for both low light effectiveness (f/1.x rated) and for Depth of Focus (ease of acquisition).
It is using a color filtered sensor which discards ~ 60% of available light (see above for low light).
It autofocuses at the selected aperture up to ~ f/8 typically, for increased Depth of Focus and exposure preview (at the expense of light).
The autofocus system sees what you see (a DSLR does not)... if what you see is dim/low contrast/significantly out of focus it will have more of an issue.
The mirrorless PDAF is functionally the same as a split prism viewfinder, a DSLR's PDAF module is quite different (although the very basis is the same).
And there are more possible issues/differences...

To compensate for all of these shortcomings the mirrorless PDAF function is typically operating in some form of fully Auto Mode (i.e. face detection, eye tracking, etc)... the newer, smarter, and more advanced those Auto algorithms are, the better the AF will be.

Thanks for the excellent explanation
Am I correct in assuming that the mirrorless system won’t have the same focus errors that you can have have with DSLR systems ? On my DSLR kit I needed to do micro focus adjustments
I have changed to mirrorless, R5 it’s amazing the focus is spot on every time

 

[robj20]

Thanks for the excellent explanation
Am I correct in assuming that the mirrorless system won’t have the same focus errors that you can have have with DSLR systems ? On my DSLR kit I needed to do micro focus adjustments
I have changed to mirrorless, R5 it’s amazing the focus is spot on every time

No mirrorless also use contrast detect focus which means accurate focus. Also because it's on the sensor it means no need for micro adjust.

 

[simon ess]

Perhaps I' ve got used to it but I don't find my X-E3 to be noticeably slower than my old Nikon D7000.

It's always accurate though.

 

[LCPete]

No mirrorless also use contrast detect focus which means accurate focus.

Ahh I see thanks, so as it works from the sensor if the lens calibration is out it doesn’t matter

 

[the black fox]

Not a particularly challenging scenario - the bird's flying flat and level, parallel to the plane of focus, not to mention being at relatively slow speed.

I think the expression is “whatever”

 

[sk66]

Ahh I see thanks, so as it works from the sensor if the lens calibration is out it doesn’t matter

No, if the lens is messed up it can still matter; but that's not what AFMA actually compensates for.
With a DSLR there is a secondary light path for the PDAF module's separate images (as many as six per focus point). And if the two light paths are not exactly the same distance then the two will be focused at different times/points (sensor image/PDAF images). And since they don't talk to each other, the recorded image is out of focus. AFMA is actually a software offset telling the PDAF images to be less in focus (offset in phase/position) so that the sensor image is more in focus... it's easier and more practical than adjusting either sensor's physical position. (to a lesser degree it also compensates for focus (aperture) shift and spherical aberration effects, which are variable by lens)

No mirrorless also use contrast detect focus which means accurate focus.

Contrast detect AF is not necessarily more accurate... it can be more accurate than the PDAF of a DSLR due to the distances variable above.
A mirrorless needs to switch to contrast detection, because once the image is in focus there is no longer two images to compare for a phase offset (but it can continue to monitor for a phase offset to reoccur and then recorrect). Whether the contrast detection mode will be sharper really depends on the resolution of the two modes and what they are given to work with. It can actually be less accurate because it is slower and dumber.

 

[LCPete]

No, if the lens is messed up it can still matter; but that's not what AFMA actually compensates for.
With a DSLR there is a secondary light path for the PDAF module's separate images (as many as six per focus point). And if the two light paths are not exactly the same distance then the two will be focused at different times/points (sensor image/PDAF images). And since they don't talk to each other, the recorded image is out of focus. AFMA is actually a software offset telling the PDAF images to be less in focus (offset in phase/position) so that the sensor image is more in focus... it's easier and more practical than adjusting either sensor's physical position.


Contrast detect AF is not necessarily more accurate... it can be more accurate than the PDAF of a DSLR due to the distances variable above.
A mirrorless needs to switch to contrast detection, because once the image is in focus there is no longer two images to compare for a phase offset (but it can continue to monitor for a phase offset to reoccur and then recorrect). Whether the contrast detection mode will be sharper really depends on the resolution of the two modes and what they are given to work with. It can actually be less accurate because it is slower and dumber.

Thanks Steven for the excellent explanation I understand now

 

[saltireblue]

I have the X-T3 and have never had cause to complain about the AF on it, no matter what lens is attached...
Except for the 35mm f/1.4. It would hunt all over the place and take its time about it too. So much so, that despite loving using it wide open, I was so frustrated that I got rid of it.

 

[sk66]

money where mouth is time ,subject peregrine falcon the fastest bird in the world.

I would suggest that a smaller passerine photographed at a higher magnification would be much more challenging... but that doesn't mean anything really. There are times it can be surprisingly good/better, and times/situations where it can be surprisingly bad/worse.

 

[gman]

Literally just posted this elsewhere but I guess relative to the OP's opening post, so this is my money where mouth is lol:

Sony A9 + Sony 35mm f/1.4 so a big old bit of glass to shift:

An unexpected fast grab shot with a puppy coming straight at me full speed, so a fairly challenging scenario and although I did have good light I don't think it would have been a problem if it were darker as the A9 excels at ISO640+. Focus is perfect on her eyes:

 

[gman]

This one I was ready for:

 

[andrewwnbanks]

The Fuji system AF is just poor. Sony and Canon have the best AF currently, but you have to learn to love the Sony cameras. Very irritating menus and sensors are so prone to dirt. Currently loving my R5.

I always wanted to love Fuji but damn why can’t they fix the focusing.

 

[nandbytes]

The Fuji system AF is just poor. Sony and Canon have the best AF currently, but you have to learn to love the Sony cameras. Very irritating menus and sensors are so prone to dirt. Currently loving my R5.

I always wanted to love Fuji but damn why can’t they fix the focusing.

You seem to be enjoying reviving some old threads

Sony's menu system has since changed. It is no more or no less prone to dirt than any other brands. It's not like they install dirt magnets.

 

[AndrewFlannigan]

You seem to be enjoying reviving some old threads

Always a fun pastime!

The focussing speed champion in my stable is the Panasonic G9 / 100~400. It's not perfect but this example is much less than 1/10th of the original image area...

 

[cambsno]

The Fuji system AF is just poor. Sony and Canon have the best AF currently, but you have to learn to love the Sony cameras. Very irritating menus and sensors are so prone to dirt. Currently loving my R5.

I always wanted to love Fuji but damn why can’t they fix the focusing.

User error?

While the focussing is not up to my old D750 it’s pretty good and not had issues with it.

 

[Plain Nev]

I have the X-T3 and have never had cause to complain about the AF on it, no matter what lens is attached...
Except for the 35mm f/1.4. It would hunt all over the place and take its time about it too. So much so, that despite loving using it wide open, I was so frustrated that I got rid of it.

You should have switched it to manual and used peaking.

 

[nandbytes]

User error?

While the focussing is not up to my old D750 it’s pretty good and not had issues with it.

It's very lens dependant on Fuji. Some of the newer lenses are great at focusing and some of the older ones rather slow and sometimes "jerky" (like older screw driven lenses)
That is not to say it is bad but others (a lot of them being newer too) have faster and smoother AF motors.