Got the Sigma 10-20mm f4-5.6

[PaulWog]

I'm having fun with it. It's definitely fun playing with the ultra wide.

I'm wondering if the cropped 1:1 portions of test photos are within tolerance. On the left is regular focus, and on the right is liveview focus. I don't have focus calibration on my camera. I'm going to go do some more test shots, but I did 5 test shots in each mode of the bricks, and every single one turned out this way (same settings) @ 20mm.

Both images shot at f/7.1. Both at ISO 250. Image on the left is 1/400 of a second, image on the right is 1/640 of a second. I was very still with handholding technique. The difference in shutter is just due to aperture priority. I'll go do full manual test later. I want feedback asap though since I have a small exchange time-window. Otherwise, I'm having a ton of fun with the lens.

 

[dxqcanada2 1]

Hmm, the left looks out of focus.

 

[PaulWog]

Hmm, the left looks out of focus.

It is. The lens is backfocussing consistently under certain circumstances, and under other circumstances it's behaving just fine. Live View, as expected, focuses bang on perfectly. I just want to make sure the lens is acceptable throughout the 10-20mm range if I'm doing a closer focus & not entirely landscape.

I'm *extremely* happy about this lens, but I'm suppressing the celebration phase until I've finished running a gamut of tests.

edit - I just ran a series of other photos through. A few at 10mm, a few at 14mm, and a few at 20mm. I compared regular focus vs. liveview contrast focus. Liveview is basically the reference point of perfect focus. 18/20 photos turned out super sharp in regular focus mode compared to the liveview contrast focus ones. The only big issue I had was a test I did taking a shot of my dog at 10mm from about a meter away. I had consistent and bothersome backfocus unless if I used liveview.

I'm pretty happy since most of the issues I've encountered so far are non-issues. I'll be taking this lens out for a spin tomorrow for a day with the girlfriend. If all goes well, it's a keeper

 

[Derrel]

That flat concrete, or dog fur for that matter, might not be providing enough contrast for the focus system. The thing is, phase detection AF, like d-slrs use, depends on the system being able to compare data and determine if it's "IN" focus, or "OUT" of focus...the problem is, at 10mm, a lens of f/4 has deep depth of field, so the difference between "in" and "out" of focus is like a looooong, slippery slope; Phase detect works much better when the differences are like a plateau, and the drop-off. With a telephoto, like say a 300mm f/2.8, focus is either wayyyyy out, out, in, a little out,k then suddenly wayyyy out, so a 300/2.8 focuses smartly, easily, readily. Wide-angle lenses, especially ultra-wide lenses, have sooooo little magnification, and thus so much depth of field, that at f/4, or f/5.6, there's not a clear-cut in/out, and the AF system once it thinks it's on, will let you shoot. Because, after the lens is stopped down, beyond three feet, there's a lot of DOF. Phase detection AF is, at one level, a dumb machine, trying to think.

My experience is this: focus by scale, then shoot. 1 meter, 1.5 meters, 2 meters, 3 meters, 5 meters, done. Estimate the range, set it, and shoot.

THe concrete pavers are a LOW-contrast target to a low-magnification lens. Using a multi-area AF pattern on a flat target might help.

Also, at low magnification and wide-angle, the AF area brackets cover a loooot of real estate. You might "think" or even be "shown" by the finder's AF bracket that you've selected the dog...but at 10,15,20mm, the dog might actually be missed. The AF sensors are sometimes a bit offset from the AF indicators.

Focusing wide-angle lenses has always been a problem because of the above issues.

 

[PaulWog]

WONDERFUL information. Thank you so much

I'm going to begin celebrating.

 

[PaulWog]

Oh, something interesting to mention: The box says "D5300 compatible". It's not a sticker, it's the box itself that the lens came in. Interesting. I guess Sigma still produces the f4-5.6 lens?

 

[PaulWog]

Backfocus is still an issue after taking it out today. Not major since it's a wife, but it makes 20mm a bit annoying. In live view it's perfect. I'm keeping the lens pretty happy.

I may actually only manual focus with this lens due to the aperture and width. Might be quicker and more convenient. I don't need to really even look through the viewfinder to get the focus on manually.