A mirror lens is usually cheaper, easier to focus,
always a lot lighter (allowing it to be handheld) and
easier to construct so it might be sharper (big might
there though).
Cons are that it almost always has a fixed apeture
(usually at f8 or so). Might not have a tripod mount
so its tougher on the camera when mounted on a tripod.
The biggest drawback though is that it'll always have
doughnut out of focus highlights which can look simply
horrible so it has bad bokeh.
A glass lens at that length is usually very
substantial meaning its a tripod or bust, however
there are advantages. Variable apeture which is almost
always faster. Much better out of focus highlights.
This comes with a big weight/expense penalty though.
If you buy a long faster telephoto the price
skyrockets.
Basically if you are just rarely going to use a long
tele like that a cheaper mirror lens will probably
suffice. If you are going to be using long lenses a
lot though a glass lens would be a better match.
Mark Lloyd
--- Charles Monroe <chasmnro@xxxxxxxxxxx> wrote:
What are the pros and cons of a long focus versus
a mirror lens of
the same effective mm length?
> Charles Monroe
I got interested in a mirror lens for a while, but sort of lost
interest because of the doughnuts on out of focus highlights, and
even when there are no sparkly highlights the examples of bokeh I saw
on the web are really ugly, sometimes even creating out of focus
double images. Many of them also have poor contrast and light loss.
There are exceptions to that and I think the Oly is one of the better
ones.
--
Winsor Crosby
Long Beach, California
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