I noticed a Wetpixel post regarding the Seacam D100 that expressed concern that the S180 would block a portion of the LCD screen. Which is in fact true. Because of the space needed for all the mirrors and lenses inside both the S180 and S45 viewfinders, they are larger than a conventional housing's viewfinder. That's the tradeoff to get 1:1 viewing and +/- 3 diopter vision correction.
But with a camera like the D100, where the LCD is directly adjacent to the camera viewfinder, that can be perceived to be a problem. Fortunately Seacam also offers a Pro viewfinder. I hadn't seen one of those actually mounted on a D100 until last week, so I shot a couple of photographs of that product to supplement the Seacam D100 shots that Brant Shenkarow shot for us.
The link below shows Brant's photos, plus a few of mine illustrating:
1. D100/S180
2. D100/Pro
3. The S180 with the adjustment port off. You unscrew the back viewfinder cap to cusomize the diopter for your own vision (topside of course) and then screw the threaded/O-ringed part back in before diving.
http://www.stephenfrink.com/seacam/sc-albu...00/inc-d100.php
I happen to still prefer the S180 for my personal use, but the Pro viewfinder is a good choice for those wishing to preserve the full view of the LCD, or those who prefer to save some money. The S180 is quite a bit more expensive than the Pro viewfinder.