I recently purchased a Canon 20D and a Canon 1DmkII. Since I'm used to using the 105mm Nikkor on a 1.5x cropped camera, I wanted something that would give me a similar field of view when used on a full frame camera as I hope to own one in the future. Sigma just released a new macro lens called the 150mm f2.8 APO DG HSM (it's quite a mouthful) at a price of $600. I purchased this macro lens based on advice from Wetpixel moderator Craig Jones. It uses an ultrasonic motor for focusing, so FTMF is possible, and it's also an internal focusing lens, so the front doesn't rack out. I believe it is the fastest macro lens at this focal length and working distance.
Since I have two 8 megapixel cameras, one with a 1.25x cropped sensor, and one with a 1.6x cropped sensor, I decided to take some test photos to see what the lens is cabable of. The first set of photos was taken with the 20D and the second set with the 1DmkII:
20D Test Photos
In air, close focus with the Sigma 150 yields a field of view of about 22 mm
With the Canon 500D diopter mounted the far focus (lens focused at infinity) field of view is restricted to a field of ~87mm
With the Canon 500D diopter mounted, the close focus field of view is an astounding 16mm!
1DmkII Test Photos
On the 1D, in air, close focus with the Sigma 150 yields a field of view of about 28 mm
On the 1D, with the Canon 500D diopter mounted, the far focus (lens focused at infinity) field of view is restricted to a field of ~112mm
On the 1D, with the Canon 500D diopter mounted, the close focus field of view is about 20mm
Multiply these numbers by ~3/4 to get the field of focus behind a flat port. This will need to be tested in water to make sure that the close focus distance is not changed by shooting underwater. That's a test for another day though - hopefully on a real dive. One thing is clear though, regardless of which camera you use, this lens will shoot greater than 1:1 (35mm equivalent). In the meantime - what these tests tell me is that this lens is going to be excellent for underwater macro photography. Because of its fast f2.8 aperture, it should be able to AF in many situations. When used in MF, and in combination with a teleconverter, wet-mate diopter, or both, this lens will be capable of very high magnification.