macro - focus to infinity?

[amk1977]

Originally Posted by PaulMontgomery

Just to add my 2p. As already said, most macros can focus to infinity. However, mounting any lens on an extension tube will take away its infinity focus capability.

You're not wrong there!

I just mounted 3 stacked Teleplus AF extension tubes (12, 20, 36) on my Tamron SP90. Infinity focus is approximately 35cm (from sensor). At the macro end, closest focussing distance ss reduced from 29cm to 25cm (basically 6cm from the end or the lens).

Incidentally, does anyone know what the ratio is increased from by using the tubes?

[greenwing]

Originally Posted by amk1977

Incidentally, does anyone know what the ratio is increased from by using the tubes?

According to the formulae supplied with my Kenko tubes, you have about 1.2x magnification with the tubes at closest focus. I've scanned the formulae & would post the images, but can't be bothered with the convoluted way of posting that this forum requires.

Chris