50mm f/1.4 G Focus Shift Problems

I just picked up my new 50mm f/1.4 G yesterday and I'm quite surprised by some of its behavior. I was expecting some focus shift as the lens aperture changed from f/1.4 to f/16, but I wasn't expecting the extreme shifting that I'm observing.

Testing at about 3 feet, at f/1.4 the lens focus is mostly in front of the focus point; at f/4.0 to f/5.6 the lens exhibits normal zone of focus behavior relative to the focus point, but it begins to shift towards back focus by f/8.0. By f/16 the zone of focus is mostly behind the focus point.

Testing near infinity shows similar beahvior, but not as pronounced. F/1.4, however, is totally out of focus and I'm assuming there's still significant front focus.

I had thought briefly of adjusting the front focus, but i rejected the idea believing that this would make the back focus at the smaller apertures even worse.

Are any other owners of this lens having the same problems, or am I just lucky?

-Bruce

This is a normal phenomenon for a lens with a nice boceh at the rear site of the focus point.

http://forums.dpreview.com/forums/read.asp?forum=1021&message=30567486&q=

DB McDonald said:

Testing at about 3 feet, at f/1.4 the lens focus is mostly in front
of the focus point; at f/4.0 to f/5.6 the lens exhibits normal zone
of focus behavior relative to the focus point, but it begins to shift
towards back focus by f/8.0. By f/16 the zone of focus is mostly
behind the focus point.

Click to expand...

I don't own this lens so I can't comment from direct experience.

Did you see this test in Photozone. The focus shift at close range is quite apparent. It seems to continue well beyond the large apertures.

http://www.photozone.de/nikon--nikkor-aps-c-lens-tests/413-nikkor_50_14g?start=1

DB McDonald said:

Testing near infinity shows similar beahvior, but not as pronounced.
F/1.4, however, is totally out of focus and I'm assuming there's
still significant front focus.

Click to expand...

Yes, at further distance the focus shift shouldn't be as much of a problem.

According to this review in BJP the lens is not supposed to suffer from this focus shift.

http://www.bjp-online.com/public/showPage.html?page=836697

DB McDonald said:

I had thought briefly of adjusting the front focus, but i rejected
the idea believing that this would make the back focus at the smaller
apertures even worse.

Click to expand...

Why don't you try AF fine tuning? I suspect the increased DOF will mask the focus shift as the lens is stopped down, particularly at normal distances.

Steve

I'm hoping to avoid AF Tuning because based on the research I've done regarding this problem, I'll most likely need to adjust the lens for portrait shots and landscape shots and possibly more. This will be a huge pain ...

To be honest, if what this lens is doing is normal, I'm going to replace it with a lens doesn't exhibit such large amounts of focus shift.

Bruce

i

I don't notice this problem with my AFS 50mm.

One question though, at smaller apertures, the DOF is SOOO large that I don't think any back focus will have any visible effect. Why are u worried about focusing accuracy at smaller apertures? Is the back focus really that bad? I find it hard to believe that a 50mm lens can have focus issues at apertures like f8.

DB McDonald said:

I had thought briefly of adjusting the front focus, but i rejected
the idea believing that this would make the back focus at the smaller
apertures even worse.

Are any other owners of this lens having the same problems, or am I
just lucky?

-Bruce

Click to expand...

--
my gallery
http://www.keehian.com/gallery

My concern is more about the zone of focus than the actual focus shift. Depending upon the aperture, the zone of focus may not be where I expect it to be and elements of the image that I was expecting to be in focus may not be in focus. This will be more of a problem for portrait shots than landscape shots, but in even in landscape shots, there may be foreground focus issues.

Interesting, because in this article it is defined as a lens with only a very little focus shifr:
http://www.bjp-online.com/public/showPage.html?page=836697
.............................................................................
http://www.aczelpeter.uw.hu

Thanks for the link. The article on the lens was interesting indeed.

My copy of the lens on the D3X definitely shows significant focus shift as the lens is stopped down. After hearing my results, the dealer I purchased the lens from is going to check with Nikon and also test other samples and verify one way or another whether its inherent to the lens, or just my copy. I'm hoping it's just my copy of the lens.

DB McDonald said:

My concern is more about the zone of focus than the actual focus
shift. Depending upon the aperture, the zone of focus may not be
where I expect it to be and elements of the image that I was
expecting to be in focus may not be in focus. This will be more of a
problem for portrait shots than landscape shots, but in even in
landscape shots, there may be foreground focus issues.

Click to expand...

With your re-statement of your issue here, aren't you referring to depth-of-field as opposed to "focus shift"? As far as your expectations of what will be and will not be sharp at a given aperture, the main question I would think, is whether the object on which you specifically focused was in focus. As you probably know, at an aperture as wide as 1.4, your DOF is going to be paper thin, and will provide challenges for portrature. For example, at that aperture, you will probably only get one of the subject's eyes in perfect focus where the other will be soft. This can be good for "creative" images but for general portraiture you probably want to stop down.

What I'm saying is that because the focus shifts from front focus at large apertures to a back focus at small apertures, the zone of focus is also a moving target.

What prompted me to dig into this was when I discovered the lens front focusing on a portrait shot. A 100% crop clearly showed that the parts of the shot in focus were in front of where the AF was actually focussing. The problem is obviously worse at close distances, but even distance shots show the effect. And, before anyone asks, my other lenses focus perfectly using AF.

I am having this issue as well. Anybody else in this forum?