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Archive 2015 · So what's the deal with AF on the FE 28-70?

Jman13
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p.1 #1 · So what's the deal with AF on the FE 28-70?

So, I'm testing the FE 28-70 for potential purchase to have a lens that's convenient for tripod work stopped down on the cheap, and I'm finding that optically it's a pretty good lens. Up close, I'm getting fantastic results, with things look usable even into the corners. Of course, things are softer there than in the center, but not bad at all, really.

However, at wider focal lengths, I've noticed that the outer 50% of the frame has been utterly dreadful when focused further away, and I just couldn't figure it out. Then a few people mentioned poor AF accuracy and I started checking, and seriously: What the heck is going on here?

I noticed that when focusing further away than about 2-3m, the camera will show what appears to be a pretty accurate measurement of focus distance from me to the point I'm focusing on. Problem is, the lens isn't actually focused at that point at all. There appears to be some sweeping away field curvature at the wide end here, but I'm assuming this is due to PDAF being used on my A7 II instead of contrast detect...it detects the distance and moves the lens there. Problem is, this sucker focuses WAY past infinity at the wide end, and when focusing on a subject, say, 15m away, this is already beyond infinity for the outer regions of the frame. Focus at 4m or so and f/8, and everything is nice and sharp across the frame.

The question is, why, with this hybrid AF, does Sony not use PDAF to get the lens close, then finalize position with CDAF, like most hybrid systems do in single shot? It would seem to solve this issue that apparently many have. It's not a deal-breaker for me, as most of my work with this lens would be on a tripod anyway, and for the times it wouldn't be (general purpose work with people or sorts), I'd probably be closer up, where it seems to do fine with accuracy. But still...this really shouldn't be happening. Especially because I'm sure the engineers who designed the 28-70 know it has this behavior.

Anyway, for outdoor work and any moderately distant stuff, this is a manual focus lens, IMO. In that scenario it does fairly well. See the examples below. This is at 28mm, f/11, near the lower left corner of the frame. Now, 28mm appears to be one of the weaker areas of this lens anyway, but when manually focused, it's at least usable. Autofocus (and the AF point was put on the bottom of the tree at this framing), and it's complete garbage.

Here's the test scene (just random park/road). This is the AF frame, BTW:
http://www.jordansteele.com/2015/28test.jpg

100% crop AF:
http://www.jordansteele.com/2015/28testAF.jpg

100% crop MF:
http://www.jordansteele.com/2015/28testMF.jpg

Apr 30, 2015 at 11:58 AM

VaughnA
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p.1 #2 · So what's the deal with AF on the FE 28-70?

It works. Just like any other lens.. IMHO the 28-70 is a hidden gem of a lens for the money.

Apr 30, 2015 at 12:09 PM

Jman13
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p.1 #3 · So what's the deal with AF on the FE 28-70?

Except it doesn't. As shown above, it has real issues with stuff at the wide end at further distances. It focuses beyond infinity at these distances when using AF. I've seen two others in the past week comment similarly about odd AF accuracy issues. Optically the lens is pretty good, especially for the price.

Apr 30, 2015 at 12:12 PM

snapsy
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p.1 #4 · So what's the deal with AF on the FE 28-70?

Does it only happen when you use an outer AF area or in the center as well?

Apr 30, 2015 at 12:25 PM

Jman13
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p.1 #5 · So what's the deal with AF on the FE 28-70?

It happens when I focus anywhere in the frame. There is field curvature with the edges going away from the center, however when focusing at a distance even the center seems to be slightly beyond the optimal point of focus while the edges go completely off beyond infinity. Focusing at longer focal lengths or at the wide and when focusing closer than about 2 m is no problem.

snapsy wrote:
Does it only happen when you use an outer AF area or in the center as well?

Apr 30, 2015 at 12:32 PM

snapsy
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p.1 #6 · So what's the deal with AF on the FE 28-70?

Jman13 wrote:
It happens when I focus anywhere in the frame. There is field curvature with the edges going away from the center, however when focusing at a distance even the center seems to be slightly beyond the optimal point of focus while the edges go completely off beyond infinity. Focusing at longer focal lengths or at the wide and when focusing closer than about 2 m is no problem.

I have this lens and will try some focusing experiments with my A7 later today. Until then here is an infinity IQ test I did on my copy a long time ago. I believe these were all MF:

Sony 28-70 FE on A7 Landscape IQ

Apr 30, 2015 at 12:45 PM

snapsy
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p.1 #7 · So what's the deal with AF on the FE 28-70?

Also, try with Live View Effect OFF and ON. This will indirectly control whether the lens is stopped down during AF.

Apr 30, 2015 at 01:18 PM

VaughnA
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p.1 #8 · So what's the deal with AF on the FE 28-70?

Why can't I see the original post on this thread? I thought it was a thread title with no entry.

Apr 30, 2015 at 02:05 PM

Jman13
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p.1 #9 · So what's the deal with AF on the FE 28-70?

I don't know. Do you have me hidden? (I suppose if you do, you won't see this either)

Apr 30, 2015 at 02:10 PM

TheEmrys
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p.1 #10 · So what's the deal with AF on the FE 28-70?

Pdaf only is on for af-c/tracking. I believe it was in Friedman book that it is for power savings.

What were the settings for your shots? Mostly aperture and af method.

Apr 30, 2015 at 02:14 PM

TheEmrys
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p.1 #11 · So what's the deal with AF on the FE 28-70?

After re-reading, its f/11 and probably single point af. What happens in dmf?

Apr 30, 2015 at 02:17 PM

Jman13
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p.1 #12 · So what's the deal with AF on the FE 28-70?

I was using DMF, as I'd focus and take the shot, but then found that if I would adjust the focus closer with manual, the shots were tremendously sharper.

What's odd is that it's only at the wide end (28-40mm) and only beyond about 3m. Close up, it's bang on.

Apr 30, 2015 at 02:19 PM

shirozina
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p.1 #13 · So what's the deal with AF on the FE 28-70?

AF rubbish on these cameras for speed and accuracy. Use MF with the mode set to stopped down and use the focus magnifier. Turn up sharpness to max I the picture profile to help if you shoot RAW. This lens is not bad at all when used like this at f11.

Apr 30, 2015 at 03:37 PM

TheEmrys
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p.1 #14 · So what's the deal with AF on the FE 28-70?

And DMF showed it in-focus? Did you try it with Focus Magnify? If not, it would probably be worth your time. Something is a bit off. Not sure if it is all of them, or just your copy. Very odd behavior.

Apr 30, 2015 at 03:38 PM

lonleyppl
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p.1 #15 · So what's the deal with AF on the FE 28-70?

I feel like I've seen this with my copy as well, though I just dismissed it as iffy AF.

Of course, when I look at a few pictures from yesterday, at least the center is fairly sharp at infinity, for a shot at 28mm and f/8... This was using AF-S, in single shot drive mode and center focus area though.

Unfortunately, focus settings are saved in EXIF, so I'll have to do some test shots to check. I can do this if you're interested, though it may take me a few days to get around to it...

Apr 30, 2015 at 04:21 PM

Jman13
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p.1 #16 · So what's the deal with AF on the FE 28-70?

If I AF at a distance, the edges are focused beyond infinity. If I correct it with DMF, of course, the images are fine, but when I first start manually focusing you can see the edges are out of focus.

I did many tests after work, though not as controlled as I'd like after viewing the images at home. There's definitely some funky stuff going on with how the lens works, not just with regards to AF, though it is part of the issue. When the center is truly at infiinity, the center is crazy sharp, but the edges (and by this I mean anything outside the center 1/3) go to complete mush. Focus near hyperfocal distance, and the center isn't quite as sharp, but the lens shows pretty darn good cross-frame sharpness. I don't know if the design just doesn't handle the wide focal lengths when set to infinity focus or if it's something else. It's just bizarre that focusing with the edge doesn't help.

I did get some OK shots when I manually focused and checked for sharpness in foreground and background. It's good here (though not excellent) even into the corners. These are all manually focused.

@28mm:
http://www.jordansteele.com/2015/stump_city.jpg

@35mm:
http://www.jordansteele.com/2015/northbank_patio.jpg

100% crops from near to far of the one above:
Lower left corner:
http://www.jordansteele.com/2015/northbank_crop1.jpg

And now the distant scene on the left edge:
http://www.jordansteele.com/2015/northbank_crop2.jpg

I'll take that all day long....I just need to be really careful where I put the focus when shooting at the wide end at a distance.

TheEmrys wrote:
And DMF showed it in-focus? Did you try it with Focus Magnify? If not, it would probably be worth your time. Something is a bit off. Not sure if it is all of them, or just your copy. Very odd behavior.

Apr 30, 2015 at 05:15 PM

mmurph
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p.1 #17 · So what's the deal with AF on the FE 28-70?

Thank you for sharing!

I just got my A7II yesterday. I have a 28-70 on the way, that will be here sometime next week.

It may take me a while to get some other basic things out of the way first, but I will try to test my kit out when I get the time.

+++

And if it finally gets warm enough. I left Florida April 15, because family stuff back here in Michigan. Florida was getting too hot (after being perfect in Dec, Jan, Feb, Mar). Michigan has been too cold - 40's and grey yesterday (perfect today & tomorrow though). I suppose that Tennessee would have been "just right" - "The Goldilocks State!"

Cheers!

May 01, 2015 at 12:34 PM

TheEmrys
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p.1 #18 · So what's the deal with AF on the FE 28-70?

I think it could also be the Baby Bear, also.

May 01, 2015 at 02:12 PM

Jman13
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p.1 #19 · So what's the deal with AF on the FE 28-70?

Well, after shooting with the lens a fair bit this morning, I think I'm going to go ahead and keep it. It's still annoying that I have to pay close attention on wide distant focusing, but given my typical use scenario here it's not a big deal, and the optics are pretty good, especially considering the price, if I manually focus for landscape work. It also does great if I'm shooting people or events (likely with flash), since I'm going to be closer to them and not generally shooting at 28mm and 15m away.

Anyway, most of my work will be done with my FD glass, which is performing very well. I may just have to pick up a 55/1.8, just because it's so good, but that's going to be it for the native glass for quite a while, as the rest is just so expensive, and it's not my primary system, but I'll likely use it for a lot of landscape work, where manual focus is just fine.

May 01, 2015 at 02:36 PM

uscmatt99
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p.1 #20 · So what's the deal with AF on the FE 28-70?

I had a frustrating learning curve with the 55/1.8 on an A7, coming from using mostly manual focus glass on Sony cameras, or Nikon cameras with AF lenses. Focus with the A7 and 55/1.8 was completely inconsistent, sometimes perfect, sometimes beyond infinity, sometimes slightly off. I tried single point, multipoint, always in AF-S. I tried DMF but fine-tuning the focus is a pain on the focus by wire lenses.

My issues were solved by using back button focus and disabling AF with the shutter release button. Interestingly and painfully, I have to release the back button before firing the shutter release for it to maintain perfect focus. This works nearly 100% of the time, and maintains perfect focus when I recompose. If I keep the back button depressed while firing the shutter release, it will often miss focus by a smidge, almost as if it starts hunting anew again.

Between that and having one of the 55/1.8 lenses with weird left sided field curvature, I almost returned the lens. But I'm glad I kept it as I've gotten some photos that would have been tough with MF lenses. I hope that future iterations of these cameras work out the AF like the other mirrorless makers seem to have done more successfully.

May 01, 2015 at 10:16 PM

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