[Peterg984]

what are these lenses like? they seem very small in length to be 500mm.

cheers

Pete

[Joe T]

Mirror lenses are always a compromise. They usually offer a fairly small aperture too - I assume the one you are looking at is f8?

Are you looking at this one by any chance? My adivce: dont tuch with a very very very long stick!

[CT]

Originally Posted by Peterg984

what are these lenses like? they seem very small in length to be 500mm.

cheers

Pete

Mirror (catadioptric) lenses achieve the short physical length and the long focal length by bouncing the image back and forth off mirrors within the lens. They usually have a fixed aperture of f8 or f11 so you're limited to using them only in the best light. They also typically give a pronounced doughnut effect with out of focus highlights in shots.

Best avoided IMHO, unless you're going to go for a recognized brand, and even then, they're really a cheap alternative to a conventional lens. You can usually fit small neutral density filters over the rear lens element which is the only way (with the fixed aperture) to have any control over exposure.

They're optically not as good as a normal lens, and that one on fleabay looks really cheap and nasty as Joe says.

[Peterg984]

thanks for the replys and yes i did see it on fleebay, I woundered how they worked and now i know so i`ll keep well away.
Thanks

[dazzajl]

They're optically not as good as a normal lens, and that one on fleabay looks really cheap and nasty as Joe says

But.....

If I was looking to spend a little over a hundred quid on a (mostly) pointless toy I could be tempted. It's not going to produce anything like great images but I've always liked the little donuts on OOF light points.

[CT]

Originally Posted by dazzajl

But.....

If I was looking to spend a little over a hundred quid on a (mostly) pointless toy I could be tempted. It's not going to produce anything like great images but I've always liked the little donuts on OOF light points.

I don't dislike the donuts either.

When I were a lad I bought two Carrenar lenses from a special offer in AP. One was a 135mm tele and the other was a 28mm wide angle. The two lenses cost me 35 quid IIRC. The 135 was OK, but the 28mm!!

I went up Long Mynd in Shropshire to do some infra red landscape shots and I used my car parked in the foreground in a couple of them. You could see the the resolution blurring before you got to the edge of the number plate.