The Tamron 500 mm f/8 Adaptall model 55B is an interesting beast. At 600 g, it is very light and can be used without a tripod at 1/300-1/500s. Being an f/8, one and only aperture, the lens requires high ISO values to be used even on sunny days, which is less of a problem with a current dSLR than once was with film photography. These mirror lenses are not for everyone and everything but are a compact alternative to “normal” long lenses for moon shots or birds and animals. Using it for portraits is hard and not very convenient, despite the close focusing capabilities of the lens (1.7 meters, a record).
What’s nice about the Tamron is that it can be used either on Nikon or Pentax dSLRs bodies with the original Adaptall rings. Additional adapters are required to fit the Adaptall lenses on Canon or Sony dSLRs.
My experience with the lens is shallow. I don’t use a tripod most of the time, and with such focal lenght and aperture it is a must. The out of focus area mirror the central part of the lens to give some pictural effects:
In terms of sharpness, I would most likely use a faster shorter lens for a given subject. In real life use, I remember about a year ago taking pictures of the 14th of July fireworks. First, the overall setting (135mm Tokina f/2.8 lens, at f/4):
The center of the same scene, as seen by the Tamron 500 mm lens (on an APS-C size sensor). Motion blur is obvious even at web site size of the picture:
I have sold this lens for the same price that I bought it. It was an interesting experience well worth the money :-). The mirror had some slight fungi growth but was very easy to clean (the tricky part was to unscrew the ring retaining the front element). The lens built is excellent.
If interested, you can also look at the photozone review.