Lens review

Sony FE 50 mm f/1.4 GM

21 February 2023
Maciej Latałło

10. Autofocus and focus breathing


The Sony FE 50 mm f/1.4 GM is equipped with two XD linear autofocus motors and, according to the producers, they are supposed to ensure 1.9x faster performance than in the case of the predecessor, the Planar FE 50 mm f/1.4 ZA. Additionally, they claim the mechanism will be completely fluent even during filming as fast as 120 fps.

After attaching the tested lens to the Sony A7R III the autofocus is indeed noiseless and quick. Running through the whole distance range and confirming the focus takes 0.5-0.6 of a second without any wavering or play. The mechanism works very smoothly and is equally quick no matter from what direction you start.

After attaching the lens to the newer body of the Sony A7R V we haven't seen any distinct changes. The speed and efficiency of the mechanism remained very similar and it means there will be no problems connected to it.

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Photos taken both in the studio and outside showed that the Sony FE 1.4/50 GM doesn't have any problems with accuracy. The autofocus worked well and misses were few and far between.

The new Sony lens didn't show any front or back focus tendencies on any of the bodies we used in our test.

A7R III, f/1.4
Sony FE 50 mm f/1.4 GM - Autofocus and focus breathing
A7R V, f/1.4
Sony FE 50 mm f/1.4 GM - Autofocus and focus breathing

Focus breathing

Reframing images as you pass from the minimum focusing distance to infinity is presented by the following video:

A superficial measurement, consisting of a comparison between freeze-frames showed that the difference of the frame content between extreme points is about 10%. As our lens breathing tests are just being implemented, we don't have a clear scale that would allow us to assess with utter precision how high or low this level is. From a practical point of view you can say it's somewhere near medium level – this breathing will be noticeable in real life.

After attaching the tested lens to the newer Sony A7R V body it was possible to switch on breathing compensation function. It performed very well and was able to reduce breathing to practically zero but, of course, you had to pay for it with additional image cropping. It's possible that Sony engineers gave up on breathing correction deliberately, knowing that a camera software is able to do it anyway. Of course it would be better if the lens just kept the whole frame content while oversharpening – then the breathing compensation function wouldn't be needed at all.

It is also possible that the producers decided to use a slightly shorter focal length, amounting to 48 mm, just because of breathing compensation – it provides a bit of reserve in the field of view when compared to the classic 50 mm value.

Finally, let's mention the fact that, after passing to the minimum focusing distance, the lens gets noticeably 'slower' – such an effect is very pronounced in the video even though we used fully manual exposition. It stems from laws of optics and concerns mainly macro lenses with the 1:1 mapping scale. Here the scale is visibly smaller because the magnification in the minimum distance mode amounts to 0.18x; the effective aperture should have reached near f/1.6-1.7 but is evidently lower.