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June 13, 2012

Sony Nex-5n AF Testing with LA-EA2 and A-Mount lens vs Native E-Mount Lenses

Sony Nex-5n AutoFocus Testing using the LA-EA2 Lens Adapter vs Standard E-Mount Lenses

I did a quick test today with the Sony Nex-5n, LA-EA2 lens adapter, and the Sony DT 35mm f/1.8 Lens.Β  I then compared the Sigma 30mm f/2.8 EX DN lens and the Sony 50mm f/1.8 OSS lens to see how each of these lenses performed in comparison. I was in pretty decent light, so the camera had a relatively easy time.

In theory the Phase detection capable LA-EA2 lens adapter should make the focusing faster as the contrast detection auto focus is slower by design. In addition to that the focus motor of the particular lens is ultimately going to determine the max focus speed as the AF motor can only go so fast. I wish I had a SSM lens so I could show you how fast that is in comparison to these lenses. It’s at least twice as fast going from memory.

Nex-5n, Sony DT 35mm f/1.8 Lens Mounted to the Sony La-ea2 Lens Adapter

Nex-5n, Sony DT 35mm f/1.8 Lens Mounted to the Sony La-ea2 Lens Adapter

Just so you know, I shot wide open (f/1.8 and f/2.8) with all these lenses to make the focusing as hard as possible as it relates to depth of field. Note, when using the LA-EA2 lens adapter the Aperture is automatically stopped down to f/3.5 in video mode. So for the Sony DT 35mm f/1.8 lens, even though it was set to f/1.8 the camera automatically switched it to f/3.5 when I started recording video. Why exactly Sony does this is still unknown, but I was told it’s so beginners wouldn’t blow out the scene do to the 1/4000sec shutter speed limitation in combination with fast apertures. Personally, I think they did this in order to save the camcorder market and professional grade equipment. Who knows really?

The narrower the depth of field, the harder it is for the lens to focus. This makes sense as the “high contrast” area the camera is looking for is only visible for a fraction of a second with a super narrow depth of field. In other words the camera will tend to search front to back for something with high contrast. If it doesn’t find anything, it will just continue to hunt. You may have run into this issue in low light shooting wide open πŸ˜‰Β  Best bet is to switch to manual focus when this happens. When the depth of field is large, most of the scene will be in focus, so finding a high contrast area is much easier for the camera and the auto focus performance is usually much better.


Nex-5n AF Testing Video



Closing Remarks

I was in pretty decent light, so the camera had a relatively easy time. I’m going to do a low light low contrast test tomorrow!!

As you can see from the video all three lenses performed pretty good in my opinion with the A-Mount DT 35mm f/1.8 and LA-EA2 lens adapter combo performing the best. The focus transitions were smooth and the af locked on as soon as sharpness was achieved.

The Sigmas 30mm f/2.8 EX DN lens always locked on, but hunted a little bit back and forth just before it locked focus. Almost like it was making sure it locked on or something. I actually did tried this lens twice in the video to make sure it did that hunting dance both times, and it did.

The Sony f/1.8 OSS Lens performed better than the Sigma and almost as good as the LA-EA2 combo!! It transitioned a bit different though from one focal point to another. Super smooth transitions which this lens is know for, and it makes for a better viewing experience as it’s almost an ease in effect.

The Optical Steady Shot of the 50mm lens stands out to me as the most in the video however. I was hand holdingΒ  with all the lens combinations and you can clearly see how shaky the camera is. Once I put the E-Mount 50mm f/1.8 OSS lens on, it smooths right out on the video. Check it out again if you didn’t notice, as it’s really drastic how well the OSS works.

One other odd thing I noticed was both the Sony lenses focused automatically as I moved the camera from spot to spot, but the Sigma 30mm lens did not. I had to actually press the shutter re-lease to get the Sigma to re-auto focus. I’m not sure why this happened though, as I just tried it again and it worked just like the Sony lenses. Perhaps some kind of user error, but I don’t think so. A SAL (SonyAlphaLab) reader (Eli), actually reported an issue with the sigma lenses failing to focus all together and having to re-boot the camera to fix it. Perhaps it was something similar to that issue, but I’m honestly not sure. I can’t seem re-produce it.

In any event, I hope you all got something out of this video auto focus test, and please let me know what you think. I can do more tests for you if you want, just let me know and please be specific πŸ˜‰ I’ll have some time this evening to try a few things if anybody wants.

Later on,


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  1. Michael D

    Thanks for test. I didn’t like the hunting on the Sigma at all. I was shooting video on the Sony 55-210 E-Mount and I panned down from something in the far distance to something much closer, and it looked like a lovely rack focus shot. Good stuff.

    • Jay

      Hi Michael,

      I did not care for that either, but to the sigma’s defense it doesn’t do that every time. It depends what it’s focusing on. The Sony lenses are so smooth though, and the transitions are incredible!! Killer for video and in that regard, much better than the Sigma’s. The Optical Steady Shot also makes the Sony a much better option for video in my opinion. I love the 55-210mm E-Mount lens!!! That was one of favorite lenses to use as of late. My hands on review is over Here >> if you haven’t check it out yet πŸ˜‰

  2. Ro

    Hi thanks for the video, I’ve been wondering how all of these compare especially in video mode. I have just recently bought the LA-EA2 adapter and was wondering how did you get the lens to shoot at f1.8 while in video mode? Mine defaults to f3.5 and sets itself to auto exposure (P-mode).

    • Jay

      Ro, I did not get that the lens to shoot at f/1.8 in video. It’s impossible with autofocus as it stops down to f/3.5 as you said. Unless you use manual focus of course πŸ˜‰


      • Ro

        Thanks for confirming Jay. That’s what I kind of thought, but when you put “Sony DT 35mm f/1.8 Lens @ f1.8” on the titles and in the article I was hoping quite excitedly there was a trick I was missing. Maybe putting an update on the article and video to confirm the fixed f3.5 with LA-EA2 will help other passers-by not jump for joy over wide open aperture with this adapter πŸ™‚ The E-Mount 50mm f/1.8 OSS is looking very tempting to me, especially for video. Thanks again.

      • Jay


        No problem at all, and I updated the Article with a note about that specific f/3.5 issue with video and auto focus using the LA-EA2 πŸ˜‰ Thanks again for the comments and suggestion!!


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