Contrast detect vs phase detect AF

[jaapv]

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On 1/4/2021 at 12:04 AM, adan said:

and the places from which they buy their sensors are not Sony

Err.. Digilux 2, all APS cameras....

[sillbeers15]

There would be no need for the Back Button Focus Technique to be developed and popular among photographers who used the Phase Detect AF DSLRs to override camera AF 'Hit & Miss' error if Phase Detect focusing AF is perfect.

No AF system today is perfect.

Most of the time, user error of not optimising the camera settings is the main contributor of poor AF performance regardless of PDAF or CDAF system.

If user cannot even identify the AF weakness in locking focus vs sustaining focus tracking, it shows no sign of user wanting to improve AF success rate but just complaining about the matter. I find that spending time understanding the camera and more practice on different AF settings to accomodate different situations would yield better success and make a happier user.

[Tp2000]

 

I'm pretty sure back button focus came about in the early 00s in particular with press and sports photographers who spent most of the time with cameras in AF-C modes, but didn't want to have to mess around (in early cameras) with what was a less intuitive in camera experience to moving autofocus points around. So decoupling focus from the shutter button enabled that and it wasn't a byproduct of poor focus systems (I would still content that the autofocus of the 1dmk2 would be perfectly performant these days), but allowed focus and recompose for photographers who didn't have the time to quickly switch AF modes either. 

I agree that understanding the limitations and features of an autofocus system is an important consideration for any user (and if you're spending this much on a camera, expecting it to just work without taking time to optimise the performance is arguably lazy).

However, you can only optimise something to perform within the limitations ultimately defined by the camera system itself. Which takes you beyond user error. 

No AF system is perfect, some some are considerably more performant in certain situations than others. 

 

 

 

 

[Tp2000]

1 hour ago, sillbeers15 said:

There would be no need for the Back Button Focus Technique to be developed and popular among photographers who used the Phase Detect AF DSLRs to override camera AF 'Hit & Miss' error if Phase Detect focusing AF is perfect.

No AF system today is perfect.

Most of the time, user error of not optimising the camera settings is the main contributor of poor AF performance regardless of PDAF or CDAF system.

If user cannot even identify the AF weakness in locking focus vs sustaining focus tracking, it shows no sign of user wanting to improve AF success rate but just complaining about the matter. I find that spending time understanding the camera and more practice on different AF settings to accomodate different situations would yield better success and make a happier user.

I should add, I see some of the photos that you post of birds (including the one just now in the SL2 image thread) and it is clear that you have mastered the autofocus on the SL2  

[adan]

3 hours ago, jaapv said:

Err.. Digilux 2, —for which Panasonic sourced the sensor, not Leica. Leica just glued their Dot on the front - while negotiating with Kodak for their own sensor purchases (DMR, M8).

all APS cameras.... <<no comment >>

 

[jaapv]

4 minutes ago, adan said:

 

There are suggestions that Panasonic relied on Leica for the design. So who rebranded whom?

[tom0511]

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With all respect and love for the SL/SL2 and other contrast AF cameras, with all its advantages.

I disagree that it is just about the user learning the camera and AF. C-AF from a good sports camera like for example the Nikon D500 is just in another league.

I dont think one needs this for occasional kids and pet shots, and therefore I prefer the SL2 as my most used camera system. I still hope for a sensor with contrast and phase AF (like the Sony A9) in future SL models.

[hillavoider]

On 1/5/2021 at 11:29 PM, sillbeers15 said:

There would be no need for the Back Button Focus Technique to be developed and popular among photographers who used the Phase Detect AF DSLRs to override camera AF 'Hit & Miss' error if Phase Detect focusing AF is perfect.

No AF system today is perfect.

Most of the time, user error of not optimising the camera settings is the main contributor of poor AF performance regardless of PDAF or CDAF system.

If user cannot even identify the AF weakness in locking focus vs sustaining focus tracking, it shows no sign of user wanting to improve AF success rate but just complaining about the matter. I find that spending time understanding the camera and more practice on different AF settings to accomodate different situations would yield better success and make a happier user.

you have drank alot of leica cool aid bud, the AF on the SL2 is CRAP and the whole world knows it 

[sillbeers15]

1 hour ago, hillavoider said:

you have drank alot of leica cool aid bud, the AF on the SL2 is CRAP and the whole world knows it 

Leica cool aid I had none.

Real world experience on getting sharp AFC tracking results from SL2 I have many. Below shot was only taken 3 days ago on SL2.

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Blue Throated Bee Eaters after bath-1020663 by sillbeers15

 

[RBB]

On 1/3/2021 at 5:30 PM, BernardC said:

Summary: Phase-detect = speed; contrast-detect = accuracy.

Good to know: Mirrorless phase-detect cameras try to switch to contrast-detect for fine focusing, when time allows. This would be the best of both worlds, except that sensors with phase-detect elements often exhibit banding issues. Phase-detect SLR cameras have sensors in the mirror box, so they don't have that problem.

In-Depth: Phase detect works by using two sensors: one in front of the image plane, and one behind. That's how it finds the direction of focus really fast (unless the lens is severely de-focused). The distance between these two sensors determines the minimum aperture that the sensors can work with. Basically, if the distance is within the depth of field for a certain lens, the camera can't tell front from back anymore. That's why you often hear about cameras that can't AF with slower (5.6 or 8.0) lenses. What you don't hear as often, but is equally true, is that phase sensors have a maximum aperture. For instance, a phase sensor might only "see" f:2.8, even if you mount an f:1.4 lens. What happens in this case? The CPU splits the difference, hoping to get something in focus. That's why you read about lenses that front-focus or back-focus on a particular body: the CPU's default guess is wrong, and their need correction tables to tell it things like "at 28mm and 1 meter, focus two nudges ahead of your best guess; however at 5 meters and 70mm, focus three nudges behind your best guess."

The Leica S medium format SLR system gets around that issue by having a lens lineup with a very narrow range of maximum apertures: f:2.5 and f:2.8 for the main range, and f:2.0 to f:3.5 for the extremes. They can pick a phase-detect sensor that matches these apertures. Note: they also offer a slower zoom, and people often complain about focus issues with that lens...

Other systems get around the limitation by combining "fast" and "slow" phase sensors. If you spread enough of them around the image plane, you'll stand a decent chance that there will be one that is close at hand. Of course, that still leaves the issue of "how fast?" and "how slow?", which can be quite a wide range: roughly between f:1.0 and f:8.0 for recent hybrid systems. Clearly not all of these lenses will work well with phase-detect AF.

Contrast-detect, which is what Leica Panasonic and Sigma use in L-Mount cameras, is potentially much more accurate. It can find the focus point with the highest contrast, which is usually also the desired sharpest point (but not always, depending on the subject). It does this the same way that many of us did with manual focus SLRs: by rocking the focus back-and-forth around the sharpest point until it is satisfied.

Panasonic's "DFD" system adds some smarts to that very basic strategy. First-off, it knows a little bit about your specific lens, so it knows how sharp the image can get at a given distance/focus point. That means it stops focusing when it gets close to optimal sharpness. It also knows a little bit about how the image looks when it is focused in-front-of or behind the image plane. In other words, it's still guessing which way to turn the focus ring, but it's an informed guess. Another thing that it can do is to apply constant micro-corrections, essentially doing a back-and-forth at a tiny scale. That's fine for stills, but it's annoying in video where backgrounds will shimmer. You can turn that off if you want.

Conclusion: You can tell why contrast-detect appeals to Leica. It's sharper, and higher-quality (less heat-inducing, space-wasting circuitry on the sensor). Modern contrast-detect is also very fast, certainly faster than anything but a pro-level SLR from a decade ago. The downside is that it's still not "the fastest." That crown still belongs to pro-level SLRs.

What's next? Unknown to many, Leica is a world leader in time-of-flight (ToF) sensor technology. These sensors build a 3D maps of your image, telling the camera where everything is. In many ways, that is the ideal design, but it hasn't been applied to cameras yet. The big money will be in machine vision.

 

thank you, very helpful

Rob

[RBB]

There is always is a lot of discusion about the AFC capabilities of the SL2. I have shot with Nikon camera's for more than 20 years and owned several camera's including the D3s and D500 en for me does are some of the fastest sports camera's then and possible still available. But it's about compare to what. If you bought the SL2 for mainly sports, you bought the wrong camera. I bought the SL2 after a comparison with the Fuji GFX 50 R and S (don't know the GFX100). I find the SL2 much more useful then the fuji's, pleasant colours, the lovely Leica look and as a bonus a much faster autofocus. Besides that's a kind of "equally" priced. There is no such thing as the perfect camera and if I use the SL2 for wildlife the AFC works for me.

[frame-it]

14 minutes ago, RBB said:

But it's about compare to what. If you bought the SL2 for mainly sports, you bought the wrong camera. I bought the SL2 after a comparison with the Fuji GFX 50 R and S

so you compared a 35mm camera to a medium format camera? 😇

[Siran]

Just a random thought, but as there is so much difference in experience some have to others with AF, is it possible that some cameras have quality control issues. The only reason I say this is the first SL2 I had was way off with AF. With the replacement I was sent, things were better, but there is no way I would be able to get a brilliant shot like Sillbeers15 posted earlier, or the lovely image TP2000 posted of his daughter with the SL2 I have. I would have to take 30 shots to get a fluky good one. If I stop down on apature my keep rate gets better but then ISO comes into play, and sometimes that's the DOF I'm looking for.

I'm confident that the issue is not my skill as a photographer (I don't mean that in an arrogant way - please dont troll me :-)) as I have owned and shot with Olympus, Sony and Nikon prior to the Leica.

[tom0511]

vor 2 Stunden schrieb sillbeers15:

Leica cool aid I had none.

Real world experience on getting sharp AFC tracking results from SL2 I have many. Below shot was only taken 3 days ago on SL2.

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Blue Throated Bee Eaters after bath-1020663 by sillbeers15

 

thats a lovely image, but I dont see why you need C-AF for such subject. IMO ciritcal are images, where the subject is moving fast towards you or away, or where the subject changes direction of movement fast.

[tom0511]

for example this are images, which I find very hard to catch with my SL2...

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[sillbeers15]

58 minutes ago, RBB said:

There is always is a lot of discusion about the AFC capabilities of the SL2. I have shot with Nikon camera's for more than 20 years and owned several camera's including the D3s and D500 en for me does are some of the fastest sports camera's then and possible still available. But it's about compare to what. If you bought the SL2 for mainly sports, you bought the wrong camera. I bought the SL2 after a comparison with the Fuji GFX 50 R and S (don't know the GFX100). I find the SL2 much more useful then the fuji's, pleasant colours, the lovely Leica look and as a bonus a much faster autofocus. Besides that's a kind of "equally" priced. There is no such thing as the perfect camera and if I use the SL2 for wildlife the AFC works for me.

Your comments about the SL2 is fair. There is no perfect camera to start with and end with.

My story with sticking only to Leica FF cameras (SL2 & M10R) is only because of the IQ produced by Leica glasses.

Leica does not have the glass & body to support sports & wildlife. Even if Leica produces beyond the 280mm focal length range, I doubt I'll be interested to own such a lens as it would be bulky & costly, making international travel tedious. My SL2 is my all rounder workhorse from landscape to wildlife and I almost only mount SL lenses on my SL2 except using M50Noctilux on it for portraits. I just enjoy taking my SL2 on to the limits of Off camera flash & AFC tracking where most Leica users shy away.

[sillbeers15]

5 minutes ago, tom0511 said:

thats a lovely image, but I dont see why you need C-AF for such subject. IMO ciritcal are images, where the subject is moving fast towards you or away, or where the subject changes direction of movement fast.

I've mentioned it in my post of the image earlier in the SL2 Images tread that I would have preferred to use MF with a reduced apeture from F4 to F5.6 using prefocus on the branch. However I was tracking the birds while they were flying in on AFC / tracking and I did not have the time to switch over to MF as it was just a short stay before both bee eaters took off.

Yeap. For fast moving subject towards the camera with a bird no longer than 20cm, the SL2 on AFC/tracking had no problem nailing sharp focus on the Stork Billed Kingfisher coming my direction at my eye level as below.

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Stork billed kingfisher in flight - 1010052 by sillbeers15

[SrMi]

Bird photography is certainly possible, see Jasper Doest's Pandemic Pigeon :). AFAIK, all images were shot with SL2 (there could be an M10R image there as well).

[sillbeers15]

10 minutes ago, tom0511 said:

for example this are images, which I find very hard to catch with my SL2...

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Did you mean you found it hard to lock focus or find difficulty in keeping the focus tracking on the subject frame after frame?

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Hallo,

Look here: Leica L-Mount

[sillbeers15]

4 minutes ago, SrMi said:

Bird photography is certainly possible, see Jasper Doest's Pandemic Pigeon :). AFAIK, all images were shot with SL2 (there could be an M10R image there as well).

I shot this with my M240 seven years ago.

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Butterfly-2 by sillbeers15