[Buddha Jones]

To make a 50mm Macro go from 1:2 to 1:1, do I need 50mm worth of tubes?

[X Man]

Yes. ...and 10 char...

*EDIT* Err, wait. You said it's already @ 1:2 didn't you? My bad. I've got no idea. Maybe half that, or less would do it. You'll have to wait a sec for someone who knows, you know. Math. ;-)

*EDIT2* Ooh, ooh! I was right, I was right... Half that will do it. So, 25mm of "tubage" should get you to 1:1 according to the Lord Google.

Regards,
Mike

[Buddha Jones]

I googled it and only got more confused.... but that is what I thought I read as well but wanted to make sure.

[gofour3]

Use a #3 Pentax Auto Extension tube, which is 26mm or a Manual tube #3 which is 28.5mm.

Phil.

[Canada_Rockies]

To make a 50mm Macro go from 1:2 to 1:1, do I need 50mm worth of tubes?

Buddha, to take a 1:2 lens to 1:1, you need additional extension of half the focal length of the lens. 1:1 means that the lens has extension of exactly the same amount as the lens' focal length. If the lens already has enough extension to get to 1:2, it has half its focal length in the focusing helical, and you need another half.

My M 100mm macro uses a 50mm tube to switch the range to between 1:2 and 1:1 from infinity to 1:2.

[gofour3]

Buddha, to take a 1:2 lens to 1:1, you need additional extension of half the focal length of the lens. 1:1 means that the lens has extension of exactly the same amount as the lens' focal length. If the lens already has enough extension to get to 1:2, it has half its focal length in the focusing helical, and you need another half.

My M 100mm macro uses a 50mm tube to switch the range to between 1:2 and 1:1 from infinity to 1:2.

Yep I also have a Pentax 50mm extension tube for my K100/4 macro and it does the trick.

Pentax does not make a 25mm tube for the 50mm macro, so you need to get the set and use the #3 tube, in either the auto or manual version.

Phil.