Sigma 35mm f1.4 DG HSM

AchimT

AchimT

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On my lens, with manual focus and AF, objects in the infinite range are sharp when the infinite marker on the lens matches the fixed marker. But the focussing ring can still be rotated a couple of millimeters further, which makes things in the infinite range unsharp again.

Is this the same for other users of this lens?

I also noticed that I have an area between approx. 12 and 14 meters in which AF cannot get a sharp focus at f1.4, and even with the aperture closed a few stops, objects in that range look a tad blurry.

The lens is tack sharp everywhere below and beyond that area and takes beautiful pictures, but in that area AF doesn't get a sharp focus.

Has anyone done sharpness tests using AF like me (testing AF at f1.4 and e.g. f8 for a range of distances from 1ft, 2ft, 3ft, 4ft, 2 meters, 3 meters 5 meters etc. up to maybe 20 meters and then to infinite) and can confirm that they have either found or not found such a behaviour?
 
Don't own it so can't help on that front, but it might be worth buying or borrowing the Sigma USB dock.
 
On my lens, with manual focus and AF, objects in the infinite range are sharp when the infinite marker on the lens matches the fixed marker. But the focussing ring can still be rotated a couple of millimeters further, which makes things in the infinite range unsharp again.

That movement beyond infinity is necessary to permit the autofocus system to work. To get the lens focussed on infinity it will seek to focus beyond that then move back until sharp focus is achieved.
 
Thanks Laudrup.

I have the dock, and in the process of testing/making adjustments noticed that when everything else was perfectly sharp, that particular area was not. The software only offers one range for everything beyond around 4ft, so no separate adjustments possible in that range. For the area below approx. 4ft, you have 3 sliders.
 
I have not noticed any of these issues with my lens. I will try your specific settings when I'm back from work and report back
 
e-FhPro, I might not have noticed this issue, had I not been experimenting with the USB dock. In that process I looked very closely, of course. If I would just have taken pics of my kids or the landscape, I'm not sure I would have noticed it anytime soon, or maybe not at all. I have not seen it in any of the 'real' images I took, but I will search them when I have time to see if that issue becomes apparent in any of them.
 
Just as a side note garnished with a slightly bitter smile, when I asked my local dealer about it, he said this was a sign of my sample of this lens not being good. He said making sure infinite is at the end of the scale, is one way of testing whether the innards of the lens have been assembled properly.

Please understand me correctly, I think what you say is true. I just tell this as an example how difficult it is sometimes to gather reliable information.

Maybe I should add that I tested the blurred area with the D800, but on AF-S (single point, with only the center point used). So it has nothing to do with the left AF issue on some D880s.
 
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I got the dock and simply updated the firmware using it - I have yet to really test MA and then try understand how to tweak the results using the dock software. It's not the simplest program to use from the off. I'm happy for now that the lens profile has been updated and all seems well. At least for standard shooting.
 
Many lenses will "focus" past infinity.

Don't worry about it.
 
Thanks for confirming this Alan.

Keith, I read elsewhere that the D800 has still not been incorporated into this lenses firmware. So I guess there could still be improvements to come.

As for the dock software, I set up a slanted line made of dominoes, the dominoes standing on their short side (i.e. long side vertical), each domino one centimeter closer to the camera than the previous one (the 'first' one being the farthest one at the far end of the slanted line), and a tad over one width of a domino to the right from the previous domino.

Then I set the camera to f1.4, focussed on each of the dominoes, and took a picture of it. This I repeated 3 times, from approx. 1ft away, 2ft away, and 3 ft away. That way, I could quickly see if there's a front or a back focus in that range.

After I had set this up perfectly for all three ranges the software offers, I went to the garden, and took pictures of concrete fence poles (nicely structured, rough surface). They're about 3 meters apart (at first I thought it's two meters, but later on I measured the distance), so in my test I initially checked distances of 3, 6, 9, 12, 15, 18 meters and infinity.

Then I noticed that there seems to be a blurry range towards the end of the test range, but inifity was sharp. First I thought maybe the poles are too far away and too maybe getting too narrow for the AF, so I photographed the grass near the poles in question, but while that looked sharper, it was far away and at an angle, so I asked my wife to stand next to the three poles in that range. When she did, I saw that near one of the poles she looked unsharp. Not dramatically so, but because I was looking for it, I noticed it.

Then I got my folding rule and started taking pictures of the house at various distances, with the result described in the opening post. The wall did not only look washed out, but actually was not sharp, not even when I stopped down to f8, although there it was almost sharp, without looking for it I would not have noticed anything I guess.

In between that, I took a couple of perfectly well focussed 'natural' pictures of people and scenery, but again I noticed that my playing kids in a certain distance were not entirely sharp. Without the testing I'd have put this down to them moving, a normal case of motion blur :) but apparently with my lens, there was more to it than that.

Meanwhile I don't think anymore that it was me doing something wrong with the dock and the software, because basically, that range is affected by only one slider, so what could I have done wrong?

The only thing I might have done wrong is if e.g. the 1/2/3ft sliders somehow affect the infinite range too in some way. But I couldn't find any info regarding this.
 
woof woof said:
Many lenses will "focus" past infinity.

Don't worry about it.
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Auto lenses need to so that the auto focus processor can make comparisons in front and beyond the spot that on which it is being directed to obtain sharp focus before locking on.
You have probably encountered the situation (perhaps in bad light) where the auto focus cannot lock on and hunts back and forth. That happens all the time, but it is usually only for a tiny fraction of a second and is not seen.

Richard (Hoppy UK), if he sees this, will probably have a much better explanation.

Prior to the advent of auto focus all my lenses were purely manual and would not focus beyond infinity. The focussing ring was physically prevented from moving past the litttle infinity symbol.
 
Had a go at my Sigma 35mm f1.4 on my D800 - F1.4 with a focus distance roughly at and between 12-14 meters and I am getting very sharp results. I am not sure if that is of any help
 
Thanks, e-FhPro. The fact that you don't have such an phenomenon in the range where I have it IMO at least hints to the fact that it is not a design flaw of the lens in that range, but just a hickup of my lens.

It would of course be interesting to see if you have such a phenomenon in another range, or if others can see something like this too.
 
AchimT said:
Thanks, e-FhPro. The fact that you don't have such an phenomenon in the range where I have it IMO at least hints to the fact that it is not a design flaw of the lens in that range, but just a hickup of my lens.

It would of course be interesting to see if you have such a phenomenon in another range, or if others can see something like this too.
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What you are finding AT seems unlikely to me, and I can't help thinking that very often AF microadjust problems are usually down to user error ;)

The only reliable way to establish focus accuracy is to choose a target where a) the camera cannot be confused (ie target is flat and square to the camera), and b) there is a 3-D element so you can clearly see where the point of sharpest focus is (ie with conclusive out of focus areas both in front and behind to confirm it).

This is much more difficult at the longer distances you're having trouble with, especially with a wide-angle with inherently deep depth of field, even at f/1.4. It's very hard to spot the exact sharpest point. Can you post an example image?

I have mixed views on the Sigma Dock, and clever though it may be, it is still entirely dependent on having accurate data to work with, provided by the user. And that is often the hardest bit.
 
The dock is the only way to update the firmware for this lens. if nothing else, it does that. And the lens + dock are still waaaaaaaaay cheaper than the Nikon.
 
HoppyUK said:
What you are finding AT seems unlikely to me, and I can't help thinking that very often AF microadjust problems are usually down to user error ;)

The only reliable way to establish focus accuracy is to choose a target where a) the camera cannot be confused (ie target is flat and square to the camera), and b) there is a 3-D element so you can clearly see where the point of sharpest focus is...

This is much more difficult at the longer distances you're having trouble with, especially with a wide-angle with inherently deep depth of field, even at f/1.4. It's very hard to spot the exact sharpest point. Can you post an example image?
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Hi Hoppy, I do by no means deny the possibility of this being a user error :) and I'm not looking for a solution, or trying to complain or 'report a bug' or some such.

I would just like to know whether others have seen this too (in which case it is probably not user error, or at least it is no longer embarrassing for me ;) ) or not (in which case I either got a bad lens, or am doing something wrong).

I agree to what you say regarding things getting difficult in that distance. Difficult to focus, and difficult to assess.

It was not a minor unsharpness, though. There was no pixel peeping necessary to see it, it was something nobody would have missed under these 'test bed' circumstances.

Unfortunately I don't have example images anymore, I deleted everything as I've returned the lens.

But I pretty much did what you described, in the end I used the wall of my house which has an excellent structure, there was good light, and I tried it even at f8, with the result that the image was sharper, but not perfectly sharp in that range.

It could well be that in that area there is a fairly substantial focus shift, I did not test this because I could not have fixed this anyway (the focus is good everywhere in that adjustment range the dock gives you except in these two meters, so if I would change anything, I'd make things worse elsewhere), and my wife and kids got tired of me running back and forth between the garden and the computer room :)

When I get the new lens, I'll test it, adjust it using the dock if necessary, and then I will report back at some time next week. Only if it was not a user error, of course. If it was, I'll pretend nothing ever happened ;)
 
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