Right before our "historic" snowfall started -- the second one of the season already -- my 85 1.8 arrived. I've never really tested a lens before, and I don't usually read many in-depth tests of lenses myself, but I wanted to try this one out. So, I tested it for sharpness and focus last night at a few apertures between 1.8 and 5.0. All of the shots were at ISO 400. I tried to focus directly on the second (middle) "A" on "SARASA." All shots were hand-held, and these are small crops of larger scenes.
f/1.8, 1/125 sec:
f/2.0, 1/125 sec:
f/2.5, 1/80 sec:
f/3.5, 1/40 sec:
f/4.0, 1/30 sec:
As you can see, the image starts to get pretty fuzzy around f/4.0, but we're also looking at a significantly decreased shutter speed. I would like to do this same test outside, in sunshine, at ISO 100. Wonder what those results would look like. Thanks to The Great Blizzard of 2010 (not trademarked :)), it will be several days before I'm able to try a test like that.
At any rate, I'm extremely pleased with the sharpness at 1.8. The focus seems to be spot-on. I don't have a lot of experience evaluating lenses, and when I read about the problems people describe with new equipment on photography sites like dpreview.com, I get worried that I should test X, Y, and Z before being satisfied with the lens. But I consider "field use" the real test -- does it take the photos I want to take and perform as expected? Again, thanks to the arrival of The Great Blizzard, it will be a few days before I know the answers.
Meanwhile, on with testing ;)
Here's one of the first shots I took after getting the lens on my 350D. It was taken at ISO 400, f/1.8, 1/250 sec:
And here's a small crop:
Now, the first thing I notice in this crop (other than the noise in the image thanks to the ISO) is a bit of what I believe is called chromatic aberration (CA) -- the purple coloring on the top of the piece, and anywhere the light is shining directly on it. The conditions for this shot were a little funky, as you can see from the full image above -- the container is sitting directly under a lamp, which is basically providing the only light for the scene. I don't know if that is contributing to the amount of CA I'm seeing here, or if this is a "flaw" of the lens at f/1.8 (and maybe the higher ISO has something to do with it?).
Anyway, the good news seems to be that it's pretty sharp (at least to my eyes). I believe I focused on the horizontal cross-piece, where the two "wings" curve around to. Considering the cropping I've done here, and the limited capabilities of my 350D's 8 megapixels, the image seems to be evidence of a sharp lens -- even at f/1.8.
I'm pretty pleased with my amateur tests, but I'm more excited to get outside and use it -- as soon as this snow stops!