asahi pentax tele-takumar 5.6/400mm
A heavy, black lens that comes in
a chunky rigid leather case, the Tele-Takumar is not a wildlife photographer's
dream, unless the wildlife happens to be asleep or in rigormortis.
I bought it for my old Pentax
Super A, but it was hardly ever used. It is a Pentax/Pentacon M42
screw mount lens, that came with a Pentax K bayonet mount adapter when
I purchased it from a 2nd hand store.
Recently, I obtained an M42 - Canon EOS adapter ring,
which makes it possible for me to use this lens on my D60. Here's a
sample of what this combination can do:

Canon D60, Asahi Pentax Tele-Takumar 400mm, f/5.6,
ISO 400, hand-held at 1/2000
Here is a 100% crop from the above image, with no post-processing
(complete with ISO 400 noise present). Note that this cactus plant is
about 150 feet away. The needles are reasonably well resolved, but I
don't expect to be counting the hairs on a rhino's snout with it.

Canon D60, Asahi Pentax Tele-Takumar 400mm, f/5.6,
ISO 400, 1/2000
More Sample Pictures
More examples of photographs from this lens can be
found in the Tele-Takumar 400mm
Samples folder.