One of the problems I have had in migrating from a compact housed camera system (G9/Ikelite) to a dSLR (D80/Ikelite) has been a difficulty in properly seeing the image in the viewfinder. Having been used to reviewing the whole scene on a decent sized LCD held some way in front of my mask, I found it a challenge cramming my face up against the dSLR viewfinder, usually letting a bit of water into the mask in the process, and then seeing just a pokey bit of the central frame and having to peer around to review the exposure information. Evidently many others don’t seem to see this as a problem (pun intended) so perhaps it’s down to my advancing years, prescription lens mask, or just lack of practice. Whatever, the outcome for the last year has been a reversion to the compact system and the dSLR housing has gathered dust. I felt I couldn’t go on like this and having read praise of the new Nauticam 180 degree viewfinder, I took the expensive plunge of purchasing one together with an adapter for the Ikelite housing. Until the recent post “Nauticam Viewfinder and Ikelite 7d Housing warning” I hadn’t seen any reviews of this viewfinder in other than Nauticam housings, so I thought that a brief posting of my experience so far might be of interest. I should point out that this experience is to date entirely above water as my buddy has been banned from donning his dive gear until imminent end of year exams are completed.
The adapter is nicely machined stainless steel and screws easily into the Ike polycarbonate housing, sealing with a single O-ring compressed against the milled recess on the outside of the housing. The viewfinder itself then piston fits into the adapter, sealing with two circumferential O-rings in grooves. The viewfinder is secured from slipping out by an internal O-ring captured in a groove and can easily be attached/detached for travelling. Externally there is an indexing plate with two small holes that serve to locate the viewfinder pins and keep the viewfinder square to the camera base. This plate is held in place by an external screwed nut. Another O-ring is supplied to go in a machined groove beneath the indexing plate and to provide smooth friction when adjusting the position of the indexing plate. Unfortunately here lies an apparent problem as either the O-ring is too fat or the groove isn’t machined deep enough, and with that O-ring in position, there’s no way the barrel of the viewfinder will project far enough through the adapter to get its internal securing O-ring on. 
All is not lost however as the adapter works perfectly well without the indexing plate O-ring. 
Perhaps this is just an initial manufacturing teething problem?
As others have commented, the viewfinder itself is a very solid and quite heavy piece of kit and beautifully finished. There is a further minor snag when fitting the viewfinder to the Ike D80 housing which may or may not be problematic with other Ike housings. The viewfinder partially overlies the 9 o’clock and 12 o’clock direction pad buttons (see photograph). As supplied, the Ike 6 and12 o’clock buttons are longer than those at 9 and 3 and as the viewfinder is pushed home, the 9 o’clock button is operated. 
This is easily remedied by swapping out the long 9 o’clock button for one of the shorter ones elsewhere in the housing. This still leaves the two direction buttons partially obstructed by the viewfinder, which is not ideal, but my naked finger can adequately operate them. I think with a gloved hand that would be more problematic. The workaround here is to set the camera to “Focus Area Selection Wrap” (Custom setting #20) so that the obstructed buttons aren’t needed. The two command dials of course duplicate other controls that use the direction pad buttons. On the other side of the viewfinder, the clearance from the Exposure Mode Dial knob is minimal, but clearance there is and I don’t see that as a problem. However it does prevent the viewfinder from being mounted upside down to avoid obstructing the direction buttons.
Now for the view. I have attempted to demonstrate the difference in view between Ike’s “Super-Eye Magnifier” (IMHO not so super and not magnified) and the Nauticam 180. The photographs below were taken through each finder with my Canon G9. All are reproduced at the same magnification/crop both with the Canon G9 lens virtually against each viewfinder guard and more realistically with a 12mm (~half inch) gap, representing eye to mask lens distance. These show the much better view with the Nauticam. For some reason I struggled to get the G9 to focus on the D80 screen image using the Ike viewfinder – not a problem using the diopter adjustment of the Nauticam viewfinder. I accept that these photographs may not be an entirely accurate representation of real life as my eye’s entrance pupil and that of the camera will be different. However these appearances do seem to accurately reflect what I see. In fact these images possibly underestimate the Nauticam advantage, as there seems to be greater flexibility of eye positioning without vignetting.
Above: Viewfinder fitted
Above: Nauticam Viewfinder view taken close to viewfinder guard
Above: Nauticam Viewfinder view taken 12mm from viewfinder guard
Above: Ikelite Viewfinder view taken close to viewfinder guard
Above: Ikelite Viewfinder view taken 12mm from viewfinder guard
I hope someone finds this useful.
Mark
