20 January 2009

LBA - Opteka 500mm F/8 mirror lens

Size comparison between the 50mm refractive lens and the 500mm cadioptric lens:
The implement has a 2" imperial scale, which is the one closest to the lens, should you not be reflexively familiar with the size of the Pentax FA 50/1.4.

This is a t-mount lens, and it is not a sharp lens. (Without the neutral sky filter in place, it's a hopelessly not-sharp lens; the filter is part of the optical formula.)

On the other hand, it's very inexpensive (~100 USD), the K20D meters exposure through it just fine, and the manual focus (the only kind it's got) works admirably with the K20D focus confirmation. The usual factor of four downscaling corrects much that might be objectionable in the sharpness department, as well; certainly this is good enough to tell what bird this is.

Calving front of a roof-glacier. It turns out one can use the annular highlights as a focus guide; if they are the smallest points they can be caused to appear as, the image is in focus.
I rather like the depth of field side effects in this one, though I can quite see how someone wouldn't want their trees to look quite so much as though the air were water.
Aoife's "smokey jazz" portrait; like the chimney, but unlike the previous three, this was taken hand held. (Also unlike the others, this got significant post processing for light levels, as well as being converted into black and white.)

Only really useful for birds in the field in the blazing bright day, but it's also outright teeny and very light; the whole package was under a pound. The lens itself is supposed to be around 300 grammes.

It does rather make me think there's a lot of development room for this class of lenses; the Minolta (now Sony) 500mm version has autofocus, and I don't see why with the modern, stuff-some-refractive-lens-in-the-optical-out designs, automated aperture couldn't be arranged.

I expect I shall get some use out of it for distant creatures. It's not like it'll be painful to carry around.

No comments: