This item is mainly designed for Canon EOS 50mm f2.5 Macro 1:2 lens. With this adapter you can upgrade the lens to an image resolution of 1:1 or double. Be sure to add it to your lens before attaching it to your camera so your electronics are properly compensated during measurement. Although you'll lose an aperture or two with this adapter, I've still taken many photos that have paid for themselves many times over with this accessory. Add a Lite Ring to your setup and watch it all really happen! A NOTICE. Since then others have reported that the 1:2 adapter can also complement other 1.7x lenses like the 100mm macro. I'd add that the use of extension tubes, bellows, and 1.4x and 2x converters provide additional interesting imaging opportunities, but be aware of the f-number deprecation. I find the enlarged rectangular eyepiece to be the icing on the cake as an observation accessory!