Friday, May 01, 2009

Vivitar K11 On Test


This post is part of the continuing saga of the Vivitar 28mm lenses made for the Pentax K-mount. Thanks to David Whiteley in Quebec I just received the Kiron 28mm f/2, which is a very well regarded lens. Though not branded Vivitar, it is in fact very similar to one of the Vivitar 28mm variants, denoted K11 at the Vivitar Bestiary I maintain. I'm going to treat them as identical for testing purposes. Read on for my first impressions.

cross of St. Mary's
That's a quick grab shot of St. Mary's Church in my neighbourhood, shot at ISO400 and f/4 on the Pentax K20D. It's been processed as I would any of my shots, and further I've toned it in a pleasing enough fashion. You can click through to Flickr for a larger version.

Here's what it looks like without some of the post-processing, again at f/4:
K11 test: cross at f/4

A similar shot now with the lens wide open for comparison purposes. Since these were hand-held the framing is not identical. This is hardly a scientific test, but the qualitative results were consistent across several other comparison pairs of photos I made. So I would say this is typical performance.
K11 test: cross at f/2

You can judge the bokeh on that photo for yourself. I think the framing is a bit nicer and the greater contrast in sharpness between foreground and background is also more pleasing. But the actual image quality leaves something to be desired. Here are a pair of 100% crops to make this more obvious.

First at f/4:
K11 test: cross at f/4

Then at f/2:
K11 test: cross at f/2

Even if you don't click through to my lens test set to see the full-size images, the difference is quite obvious. I have observed the same with all of the Vivitar 28mms; they are distinctly soft wide open. While this can be used for effect, it is not to my taste most of the time. The solution is to keep the lenses stopped down one, and treat them as through the maximum aperture was f/2.8.

Why bother buying an f/2 if it's going to be used at f/2.8? Two reasons. First, I have observed in previous tests published here that the f/2 variants are sharper across their whole range than the f/2.8 lenses. Second, the extra stop of light gives you a brighter viewfinder, something that is always useful when manually focusing.

Here are a couple more 100% crops, this time of a statue with focus at infinity. Now, the statue itself was not that far away, so the image is mis-focused. But the qualitative IQ difference is still evident, and seems to be of the same order as when the lens is close focused.

First, f/4:
K11 test: statue at f/4

Next, f/2:
K11 test: statue at f/2

Finally, I direct you to Pentax Forums where I have posted some other images in the thread First day out with Kiron 28/2. Or check out my Flickr stream.

I hope to do a head-to-head comparison against some of the other popular Vivitar variants in a couple of weeks. But for now I can say I love this lens as a "normal" on the K20D. It seems to meter faithfully and is not difficult to focus. The only down side is that the focus ring on my copy is stiff -- something I might want to have seen to eventually.

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