Sigma 50mm f1.4 DG HSM focus woes...
I just bought one myself and I had to learn t use it before I could really evaluate it. At first I thought it was front focusing horribly. For starters, it is usually front focused a litle to allow for distant objects to be in focus as well. Then, people with FF bodies like me are upset when we shoot at 1.4 just a couple feet away near MFD and expect sharp, consistent images, which is fairly unrealistic. I'll copy a post here that I made on the sample thread for this lens over at PoTN so you can read my thoughts on it. here you go:
Continuing to test, I am hoping that I have it the best I can do with MA at a simple +2. On my FF 5D2, I really am getting the picture just how thin this depth of field can be.
I was at 1.8 and focusing on a perfume bottle using 1.8. And as I took each pic I made a mental note of whether I felt that I had stayed exactly still or not. If I felt even like I had moved the slightest bit, I made a mental note of which pic I though I moved in.
Sure enough, pretty much every shot where I had the feeling I had moved, the focus was slightly out of the dof. I was amazed. And each where I nade a note that I felt like I had really been still, the shot was sharp and within the dof. These were at 1.8 with FF. That makes me realize that at 1.4 and 1.6, there are going to be several shots where it may look like the lens is misfocusing or inconsistent where the real truth is that I ever so slightly rocked back and forth out of the dof.
I am thinking that there have to have been a whole lot of people thinking this lens was inconsistent simply because they don't realize that even the slightest movement back and forth wide open can pull or push them out of the dof.
And then I was confused because I would maybe be outside or in good light and my shutter would be way up, like 1/1000, and I would think to myself "How can the blur be caused by camera movement when my shutter is so fast? Then I realized that this is not the same kind of movement. This is not movement while the shutter is open, causing equal blur all over the picture. This is swaying back & forth BEFORE you fire the shutter. If you pull back almost imperceptibly after you get focus confirmation, especially at 1.4 and 1.6, you are making that move before the shutter fires, so having a very fast shutter won't help at all. It's a completely different thing than hand shake while the shutter is open at say, 1/30 of a second.
I have heard many say they felt like this lens had an even thinner dof than 1.4 should be. I believe it, and it makes me now think that this lens has probably gotten a lot of unfair blame because of this dof.
I think I was blaming this lens and now I realize how crazy it was to move to minimum focus distance, with a FF camera, and at 1.4 and trying to get sharp pics when even the tiniest of sway can throw you out of the dof. I am thinking that with FF, and the amount of steadiness I have, that 1.8 should be as far wide as I should attempt when I am fairly close to the subject, like just beyond MFD. Since dof increases as you get further from the subject, then maybe I could go even more wide if I am quite a bit further away. I was expecting to be a couple feet away on my FF with not so steady hands and get sharp pics at 1.4, and for me, that's just crazy.
I wanted to post this so it might help others to make sure and give the lens a good work out and learn what it, and more importantly, what YOU are capable of considering your steady hands and stance. Everyone that buys one of these needs to learn its ins and outs completely to really know if it's the lens that's the problem or our own understanding of it and our own abilities to use it.
I wish everyone who first tries this lens would follow a simple formula. If you are full frame, and you get in close to the MFD, then since you are that close you really shouldn't need more than 1.8-2.2 to get loads of bokeh because being so close gives you more. Only go down to 1.4 and 1.6 if you are backed off the subject to like a waist up portrait with room on both sides.
Anyway, I am hoping plus 2 will work fine for me, I'll report back as I get more comfortable with it and post some pics too.