Sony A7 series AF behavior – taking you back to 1930s technology

Normally I am not good in ranting. It’s just not my kind of thinking. Especially with camera gear, I am more the laid-back type and can work around a lot of technical shortcomings, still feeling very comfortable and content with my equipment. No machine is perfect and why should I always worry about some stuff instead of being happy that such amazing machinery exists, giving me perfect shots with top quality?

But this time, I am really upset. And this is because of one of the weirdest decisions I have ever seen in the last years, a decision made by Sony some time ago about auto focus:

My A7 II focuses at working aperture. No matter how much you fiddle with your settings.

The result? This results in a lot of blurry shots when you stop down your aperture. And, what’s even worse, this is really unnecessary, given today’s technology and decades-old best practice in camera and lens design.

What? Why are they doing this?

Sony sends us back 80 years in camera history … seriously?

In 1936, the first 35mm SLR system camera appeared on the market: The Kine Exacta. (A russian SLR camera called Sport also was designed around the same time, but experts agree that the Exacta was the first to enter production.) The Kine Exacta offered exchangeable lenses and also, in contrast to the Contax and Leica rangefinder systems that already existed for some years, a real through-the-lens viewfinder image. This SLR system was crucial for achieving perfect focus and composition – no matter the focal length of your lens.

There was a catch, though: When you stopped down your lens, this would immediately show in your viewfinder image. The one positive side effect: You got an impression of how background blur would change. The multiple negative side effects: (1) You would also have a very hard time to fine adjust your focus as you stopped down – the added depth of field meant that it was much harder to judge focus compared to open-aperture focusing. (2) The next downside of stop-down focusing is that a stopped down lens doesn’t deliver much light to the viewfinder – so the image that you saw was much darker.

So what happened in 1936? Kine Exacta photographers manually opened the aperture of their lens to focus. Then they stopped down to take the picture.

Of course, this annoyance was noticed very early in SLR history. Mechanisms were designed to make the lenses stay at open aperture all the time, providing a crisp view for perfect focusing. Only if you took the actual shot, the aperture would automatically stop down. Since the 1950s – let’s just pick the mighty Nikon F as an example that dates back to 1959 – every serious photographer is used to this feature. The automatic diaphragm.

This was my second Nikon F, made in 1963. Of course, with automatic diaphragm.
This was my second Nikon F, made in 1963. Of course, it came with automatic diaphragm. As of late 2016, in some respect this makes it a more modern camera than my A7 II.

A technology that has proven to be right since the 1950s should not be discarded, Sony, should it? But you just did that:

My 2015 Sony A7 II – with newest firmware as of October 2016 – focuses at working aperture. Like a 1936 Kine Exacta. Wow. There’s no easy way to change that. No menu option, no nothing.

Take as an example my Sony FE 50/1.8 lens. Focusing is cool at f/1.8; as working aperture = open aperture. Focusing is still cool at f/2.8 – a lot of lenses start there and the sensor-based focusing is still up to the job. Things get worse at f/5.6 or f/8. Much worse. Let me show an example. It took me 3 shots to be sure that one of them was spot-on. No fancy AF-C or anything – just a picture of a tree.

AF showdown tree – take 1 at f/8.
AF showdown tree – take 1 at f/8.
AF showdown tree – take 1 at f/8. 100% crop.
AF showdown tree – take 1 at f/8. 100% crop.

Obviously, the picture came out blurry. See the 100% crop (click on the picture above to see it in full resolution). Was it the 1/50 of a second? The camera has an image stabiliser and I was calm. I know how to take pics. But still, my first thought was that opening slightly to f/6.3 and selecting a shorter exposure time could help. So this is what I then got:

AF showdown tree – take 2 at f/6.3.
AF showdown tree – take 2 at f/6.3.
AF showdown tree – take 2 at f/6.3. 100% crop.
AF showdown tree – take 2 at f/6.3. 100% crop.

Yeah the second picture still sucked … another try:

De Loonse en Drunense Duinen.
De Loonse en Drunense Duinen.
AF showdown tree – take 3 at f/6.3. 100% crop.
AF showdown tree – take 3 at f/6.3. 100% crop.

This time it worked. Wow. What an achievement for a 2015’s high-tech system cameras’s AF!

Please note that above I only show one example. I have actually hundreds of frames with the same problem. In fact, it took me some time to figure out what was going on at all. A camera that focuses perfectly at open aperture but fails when you stop down – that’s really something you would not expect.

I went to the Internet – into the forums and discussion groups – and yes, others have the same issues. Many other A7 series photographers. Here is just one example of such a discussion.

The crucial part is that, with several 100 frames experience, I know that not all the “blurred” ones come out as clearly blurred as those shown above. There might be much more subtle blur. As an example, this inaccurate stop-down focus might just lead to very slight errors that can increase blur only at the edges of the frame – due to field curvarture and the lens focusing just so slightly “in front” of the subject that that curvature becomes more apparent in the end. Or you have a general feeling that the picture lacks some “bite” and then think your lens is subpar.

No. It’s not the lens. It’s the AF system of your A7 series camera. It stuggles to find perfect focus if your lens is stopped down. Like the human eye would when using a Kine Exakta.

Why do they do it?

Sony of course has thought of a reason why their cameras currently behave like this. They say that some of their lenses have such a severe focus shift – that means, when you stop down after focusing, the focal plane will move so much that you then end up with a blurred picture. They are in a way correct – that focus shift exists and it is a real problem for some lenses.

I don’t see, though, why they come up with such a clumsy solution that so clearly fails. Every FE lens communicates with the camera when it is mounted. They could apply stop-down focusing only to lenses where they know they have real focus shift errors. They could also program the firmware that it would, for instance, only apply stop-down metering from open aperture to, say f/4 or something – and if you close your aperture past that setting, it would at least open to f/4 for focusing.

Last not least they could give users a menu setting that disables or enables the setting.

If you have lenses that are not affected by focus shift – and if you constantly experience real world problems like shown above – why don’t you get a choice?

There is a workaround – it takes you back to 1936 but it works.

I definitely need my camera to focus at open aperture. If you feel the same and use only AF-S and more static subjects, this might also work for you:

  1. Disable “AF on shutter” – this means the camera won’t auto focus every time you touch the shutter button
  2. Select one of the custom buttons and then assign “AF on” to this button – I selected C2 as it is located near the shutter button itself on the A7 II

Now the procedure to take a picture is as follows:

  1. Compose and open aperture
  2. Press the C2 button (or whatever one you assigned “AF on” to) to focus
  3. Close aperture manually
  4. Take picture

Easy, huh? Your index finger needs to move three times to just take one pic: From the front dial (to open aperture) to C2 to the front dial (to close aperture) to the shutter button. Clearly, Sony engineers loved how awkward camera handling back in the 1930s was?

The only good side: All this could be fixed with a firmware update. We have to hope and wait for Sony.

Cheers,
Thomas

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