Sigma USB Dock for 35mm 1.4

So I just received my 35mm 1.4 and the focus seems to inconsistent (back focusing). So my question is, do any of you guys have experience with the USB Dock and would you recommend it?

Also, is front/back focusing supposed to be consistent? For me, the majority of my shots are sharp. About 1 in 10 will be slightly out of focus.

Thanks!

Does your camera offer manual focus adjustment?

You could read this to see what its like.

HTH

hsiehjon said:

So I just received my 35mm 1.4 and the focus seems to inconsistent (back focusing). So my question is, do any of you guys have experience with the USB Dock and would you recommend it?

Also, is front/back focusing supposed to be consistent? For me, the majority of my shots are sharp. About 1 in 10 will be slightly out of focus.

Thanks!

Click to expand...

Front/Back focus is consistent in that it is always one, or the other (at the same focusing distance) and to the same degree. That being said, a lens can front or back focus at one focusing distance and do the other at a different distance. Auto-focus is not always "spot on", however, and that might be partly to blame.

Still, I like Sigma's approach to AF Fine Tuning, in that the correction is applied to the lens, not the camera body; it's a far, far more elegant solution in my opinion. The USB Docks works just fine, even if I did find it a little awkward to to use and fine tuning your lenses for Front/Back focus is something that absolutely should be done if at all possible. Since the D5300 body does not support AF Fine Tuning, the Sigma Dock is pretty much your only option.
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That makes sense. Well I've been taking photos of the same object (at the same focusing distance) and the results are inconsistent. Some will be sharp, others will be soft. Because of it's inconsistency, would you say this is caused by camera's auto focus and not the lens?

hsiehjon said:

That makes sense. Well I've been taking photos of the same object (at the same focusing distance) and the results are inconsistent. Some will be sharp, others will be soft. Because of it's inconsistency, would you say this is caused by camera's auto focus and not the lens?

Click to expand...

Hmmm... I might. But a lot of things can affect the accuracy of auto-focus. Are you shooting off a tripod, do you have good lighting conditions and are you seeing the focus confirmation dot in the viewfinder and/or hearing the focus confirmation "beep"? Also, it can be a lot more difficult to get sharp shots at, say, f/1.4 than if you were shooting at, say, f/4 or below.

Have you tried using Live View for focusing? I'm just curious if you could get consistently tack-sharp focus using LV instead. If you can, it would seem to indicate the issue is NOT with the lens.
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I was just shooting around in the house at various objects. Lighting condition was slightly dim, equivalent to ~1/30-1/80 shutter speed at f1.4. And yes, I always wait for the focus confirmation in the viewfinder.

Are there any reliable test methods to check for back/front focusing?

hsiehjon said:

I was just shooting around in the house at various objects. Lighting condition was slightly dim, equivalent to ~1/30-1/80 shutter speed at f1.4. And yes, I always wait for the focus confirmation in the viewfinder.

Are there any reliable test methods to check for back/front focusing?

Click to expand...

Okay, that's actually good because shooting that wide and that slow is one of THE BEST ways I can think of to get soft, out-of-focus shots. One of the best things you can do to help get consistently sharp shots is keeping the shutter speed at twice the focal length you're shooting at. For instance, if you're shooting at 35mm, you want your shutter speed at 1/70 or above. If you are shooting at 100mm you want your shutter speed at no less than 1/200. In order to make this happen you may need to increase your ISO. That's fine, digital noise is easily corrected for in post, an out of focus shot is pretty much a lost cause. 1/80 probably had you in a pretty safe zone, but anything slower and yeah, I'd expect some soft shots. And the depth of field at f/1.4 is going to be pretty much razor thin.

Now, if you want to fine tune the Auto-focus of your camera you're going to need get scientific on this. AF Fine Tuning means making very minute adjustments and this is no place for hand held shots in crappy light.

There are numerous ways to check to for front/back focus issues but I'd suggest you start by reading How to Use the AF Fine Tune Function. Your D5300 does not have this particular function BUT... You can use the testing procedure explained in the tutorial to find out if you need to make any adjustments to correct for front/back focus. If you do, you'll use your Sigma USB dock to make those changes.
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Alright, I'll take a look at the AF fine tune function and test the lens again when I have better lighting.

Thanks for the help!