Just got back from a week of diving with my Bluefin Pro/XA10.
KFish saw the pentamirror from XIT404 at DEMA and bought it for me.
They're also available for some still housings too.
SUMMARY: Don't just stand there, get one!
DETAILS: The pentamirror is a boxlike plastic gadget (sorry for all the technospeak ;-) ) that contains two mirrors. It has a small frame that fastens to the L&M housing with two small screws (allen wrench included) at the rear of the housing, using existing tapped holes, and partly surrounds the L&M video viewfinder. For photos, go to their web site: XIT404
In use, the rear of the box is open to allow you to look through the normal viewfinder, which on the L&M housing is tilted about 15 degrees upward. I did not find the mirror box interfered with my normal viewing. You may or may not have the same experience.
I do some closeup video, often requiring looking horizontally at the bottom of say an anemone to video a shrimp or crab. Previously this was frustrating because I couldn't always get low enough to see through the viewfinder. If there was enough bare sand, then, yes I could. But too much of this produces a crick in my neck. Now, all I do is put the housing down flat on the sand and look straight down into the pentamirror - what amazing convenience! The image is exactly the same as looking through the viewfinder, that is, up is up and left is left. As a result I got some shots that were previously impossible for me to get.
Another wonderful feature I discovered was that when nearer the surface on a sunlit day, videoing a tarpon or maybe a diver, sometimes glare would "white out" the L&M viewfinder, making it impossible to frame correctly. I noticed that when the normal viewfinder succumbed to glare, the other part of the pentamirror was perfectly viewable. So now when I encounter glare, I just look down into the box instead of horizontally, and - no glare. A very nice benefit I didn't expect.
Bottom line: If you have either problem, "whiteout" or "viewfinder too low to see through," run right out and get one!
Disclaimer: my wife bought this for me. XIT404 didn't compensate me for this review.
Edited by wydeangle, 12 December 2011 - 11:55 AM.