Sigma 50 1.4 - soft wide open or is it me?

[Alliecakes82]

Hi All,

Just received my Sigma 50 1.4 Art, it's on a D750 body and I can't get well focused image any wider than f/4. Here are a few sample images. I have never shot wider than f/2.8 before so this is all new to me. I was expecting to be blown away, but it seems grossly disappointing. Is it me or is it the lens?

Images are at 1.4, 2.0, and 4.0. The ones on top are crops.

The eye looks like it front focused maybe? I am sure I had my focus point on the eye lashed though. Argh!

Thank you in advance for your insight!

 

[Nyarlathotep]

Hi All,

Just received my Sigma 50 1.4 Art, it's on a D750 body and I can't get well focused image any wider than f/4. Here are a few sample images. I have never shot wider than f/2.8 before so this is all new to me. I was expecting to be blown away, but it seems grossly disappointing. Is it me or is it the lens?

Images are at 1.4, 2.0, and 4.0. The ones on top are crops.

The eye looks like it front focused maybe? I am sure I had my focus point on the eye lashed though. Argh!

Thank you in advance for your insight!

I think the sharpness is there, but the focus is missed in a number of these shots. If you look at the first and second shot of the battery, the focal plane is actually several mm behind the "Duracell" label. The text on the side is sharp. At high reproduction values and f/1.4, the depth of field is pretty small. Same goes for the eye. The focal plane looks to be slightly in front of the eyebrow, putting the eyelid out of focus. Same seem to hold true with the 4th and 5th shot of the batteries.

The third battery shot is right now, and at 100% and at f/1.4, this is pretty darn sharp.

You may want to check your focus technique and/or see if focus fine adjustments need to be made. For testing lens sharpness, use live view to get the appropriate focus, then when you know focus is dead on, your can rule out missed focus if the lens is still soft.

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Aaron Killen

 

[Alliecakes82]

I used LV and focused on the "+", used autofocus, and the camera was on a flat surface.

The third shot that looks really in focus at that crop is at f/4.

Sounds like I need to do more tests.

I just don't get it...playing some more...I am at 50mm, fairly close to my subject, my focus point is clearly on the eye, and the eyes look blurry.

 

[Nyarlathotep]

I used LV and focused on the "+", used autofocus, and the camera was on a flat surface.

The third shot that looks really in focus at that crop is at f/4.

Sounds like I need to do more tests.

I just don't get it...playing some more...I am at 50mm, fairly close to my subject, my focus point is clearly on the eye, and the eyes look blurry.

Even so, the focal plane seems off on a few of these images. Contrast detect isn't perfect and can lead to missed focus. Use manual focus and zoom in the view while in live view after you have used the contrast detect. See if that helps. You might find it is still missing the battery a bit.

It is quite possible your lens needs some AF fine tune. That can be performed either in-body or with the Sigma dock, assuming you have the new Sigma 50mm "Art" lens.

With regards to being in focus at f/4, it is both a bigger depth of field and spherical aberrations may be at play, causing some focus shift. Some fast lenses focal plane shifts a bit between wide open and stopped down. Generally you have to find the "best" adjustment that works for your preferred aperture. So you can make f/1.4 nail focus, but f/4 will be a bit back focused. The Sigma 50s both exhibit this to a degree.

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Aaron Killen

 

[DAVID MANZE]

Use targets that are not round, the focus point is on the side of the battery, when calibrating use flat objects so as not to confuse the AF system and AF micro adjust from there!

 

[mrjpack]

Get the dock & calibrate the lens, my 35 needed adjustment, its amazing now that it is dialed in...

 

[Island Golfer]

While I am certainly no expert in either lens calibration, or auto focus alignment, I have owned two Sigma 35mm Art lenses and two accompanying Sigma USB calibration docks. As such, I have had quite a bit of experience with the process. When I received the first lens and dock, I spent an inordinate amount of time reading and re-reading every review and tutorial I could find. Then, I put something like 10 hours, and multiple attempts at calibration, into it. But, no matter how many times I repeated the laborious process, I could not get accurate focus results. I was not experiencing the ultra-sharp images everyone was raving about. This first lens was so difficult to calibrate that I finally gave up on it; and sold both the lens and the USB dock. About a month and a half went by, during which I kept reading how spectacularly sharp this lens was. I began to think that I may have initially received a bad copy of the lens (or, even a defective dock). It happens. So, I ventured out a second time; and bought a new 35mm ART lens and USB dock. I spent about 4 hours attempting to calibrate the four zones. My results were better than what the first lens had produced; but certainly not as spectacular as I had expected. Yesterday morning, I began again. I pulled out the 35mm ART lens and mounted it on my Nikon D800E. I mounted the camera onto a tripod, and used time-exposure shots to eliminate any camera shake. Four hours later, I had the first two zones set at +20. The lens was still slightly out of focus. But, there was no more adjustment available in the USB dock. I had reached the maximum. I was about to put this second lens and dock up for sale, when it occurred to me that the camera, itself, had adjustments. So, without changing the dock adjustments, I started with the camera adjustment. When I reached +14 in the camera adjustment, it began to produce sharp images. I left the camera at +14. As for the USB dock adjustments, zones 1 and 2 are set at +20. Zone 3 is set at +10. And infinity is at +2. I was wondering if anyone else has experienced this issue? Here are two results with those adjustments. I used the near and the far end of the spectrum, as examples. Click on them to enlarge. The first was shot in the 12" zone (zone 1); and cropped to 100%. The second was shot at infinity (zone 4); and cropped to 100%.





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truview

 

[Marianne Oelund]

Hi All,

Just received my Sigma 50 1.4 Art, it's on a D750 body and I can't get well focused image any wider than f/4. Here are a few sample images. I have never shot wider than f/2.8 before so this is all new to me. I was expecting to be blown away, but it seems grossly disappointing. Is it me or is it the lens?

Images are at 1.4, 2.0, and 4.0. The ones on top are crops.

First, you are working right at the lens minimum-focus distance, which could cause a problem. Try again with the camera a little further away from the target.

Looking carefully at the f/1.4 and f/2 examples, you can see that the battery immediately behind the target is focused better than the one immediately in front. This indicates that focus has fallen further back than intended (also note the edge of the target battery is in much better focus than the center). This may simply be due to the reflections on the battery, which create a false subject at a greater distance. You should use a non-reflective target, which is also flat. The DOF in this case is much smaller than the radius of the battery, so to be fair, if any detail on the battery (even the edge) is focused, you have to give the camera credit for having focused correctly.

When focused accurately, the 50/1.4 Art will give very good detail at f/1.4, but not quite as sharp as your example at f/4, so keep your expectations in line with that. At f/1.4 and close distance like this, the DOF is only about 1mm, so very little will be in precise focus on a curved surface.

On my D800E with no AF fine-tune, this lens will very slightly front-focus, but the focus error is much less than shown in your examples.

The eye looks like it front focused maybe? I am sure I had my focus point on the eye lashed though. Argh!

The distance between the eyelashes (intended target) and the eyebrow is just a bit less than the distance between adjacent AF points. If you want to control AF precisely, you must use single-point AF, and AF-S (instead of AF-C) mode. The selected AF point must be carefully placed where you want it, before you let AF start working, and you need to make sure that neither the camera nor your subject move at all after focusing has completed.

The problem with AF-C mode, is that the camera may elect to use an AF point adjacent to the one you have selected, if the detail at the selected point is poor for focusing. You cannot control this, except by switching to AF-S mode. I do not recommend using AF-A mode, either.

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Source credit: Prov 2:6
- Marianne