Looking at the lenses I have right now, there's what seems to be a plethora around 50mm. In fact, all the lenses I'm using right now either are 50mm or are close to it. While it would be nice to say there's a master plan behind that, it's really part by design, part coincidence. Not counting lenses which I haven't used in a while and will end up selling (a Focal 135mm f/2.8 and a Kiron 70-150 f/4), my lenses fall into two categories, AF zoom and manual, legacy lenses.
The AF zoom lenses are the kit lens (14-42mm f/3.5-5.6) and tele-zoom (45-200mm f/4-5.6), which both have one end around 50mm. For many outings I take both lenses but keep one of them on the camera for most of the time. Which one I have on the camera depends on the situation, but it's also not too much trouble to swap. My camera bag is set up so it's easy to get lenses in and out, and the slowest part is taking the rear lens cap off.
What prompted this post, however, is I currently have a Canon FD 50mm f/1.4, Micro-Nikkor 55mm f/3.5, and Nikon Series E 50mm f/1.8. While it may seem strange to have three lenses of the same focal length, their purchase actually makes sense, at least to me. But there's a fourth lens in the mix, a Pentax 50mm f/2.
Pentax 50mm f/2
This lens was the first of the collection, purchased along with the Focal 135mm f/2.8 and a Pentax K1000 body (which I've since sold). I actually liked the lens quite a bit; it was small and made great pictures.
While I liked the lens, I felt I would want something a bit faster, since I ended up using it mostly because it was the fastest lens I had. It's not that I couldn't hold the lens still (image stabilization on my other lenses more than made up the difference) but I wanted shallower depth of field. For the most part I could get pretty good isolation with the tele-zoom, but wanted to experiment with wider apertures.
The other downside of the Pentax is it took 49mm filters. All my other lenses are 52mm, so not only does my polarizer fit, but I can use my reversing ring (which goes to a Nikon F mount).
Canon FD 50mm f/1.4
When I saw the FD for $30 used, I felt it would be a good swap for the Pentax. I'd gain one stop, and could use the Canon adapter which was sitting there (I used it with the Kiron zoom). It's a hefty lens, but not surprising, with all that glass.
The increased subject isolation was indeed nice, but I started to notice flaring around highlights. The following photos have quite a bit of contrast between the daisies and the background, but represent what I've been seeing. Note that the flaring is mostly cleaned up by f/2.
While in many cases the artifacts can be either avoided or won't be very noticable, but in extreme cases I also saw flare on the complementary location (relative to the image center), which I attribute to reflections between the CCD and the rear lens element.
I decided to hang onto the lens for a while, since by knowing the limitations I could hopefully work around them. I next tried putting the lens on the reversing ring to take macros. The stack was impressive, with the Canon adapter (so I could control the aperture), the lens, the reversing ring, and finally the Nikon adapter, which was attached to the camera. I didn't have much control over the magnification unless I used my bellows. However, the highlight flaring showed itself even more, and I had trouble getting any detail with this set-up.
In the end, I was less satisfied with the FD than I expected to be. However, rather than going through a lot of 50mm f/1.4 lenses (I got lucky with this one; most of them are quite a bit more) or going with the Panasonic 20mm f/1.7 (which still intrigues me), I decided to concentrate on macro.
Micro-Nikkor 50mm f/3.5
I used to do quite a bit of experimenting with macro photography, and found it quite interesting. I know I got Kellen hooked on it when I started getting back into it. When he switched over from Canon to Nikon, he was glad he'd be able to use the bellows. However, I didn't have any good lenses for macro work, so decided to get a dedicated macro lens, settling on the Micro-Nikkor 55mm f/3.5; I also picked up a 27.5mm extension tube.
This lens is extremely sharp and has very pleasing color. What's nice is it also works well at non-macro distances. If it weren't a relatively slow lens, I would have been happy with it for general 50mm-ish use.
Nikon Series E 50mm f/1.8
I had been keeping my eye on used Nikon Series E 50mm f/1.8 lenses, and when I saw one bundled with a Nikon EM hovering around $30 near the end of a Goodwill auction, I took a chance and was the winning bidder. The body seems in good shape (except the self timer seems to not work), so I should be able to get a good part (or all) of the purchase price back by selling the body.
The lens is extremely tiny, and optically seems in good shape. The focusing mechanism is a little off. I think the threads are slightly worn, since sometimes it feels like it's grinding, but I'm able to work it back to being smooth.
Wide open, it also exhibits lots of flaring, but as you can see, it's completely cleared up by f/2.8. In fact, it's greatly reduced by f/2 (about like the Canon FD at f/2). The sun was out a bit more for these photos than those for the Canon, so the Nikon shouldn't show as much flare if the lighting matched.
Which to keep?
I've already sold off the Pentax f/2, and also think I'll sell the Canon f/1.4. The Nikon f/1.8 is very close in speed, and flare cleans up on both of them up by f/2. The Nikon is much smaller and lighter (half the weight, 8 oz. vs. 16 oz. including adapters) and I can share the same adapter as the macro lens, which I'll also keep. While it's more convenient to have one adapter per lens, it doesn't take that long to swap.