What can you say about a (now) $800 accessory finder?  No one else apparently could think of anything, so I did.  Originally conceived as an accessory finder for the 16-18-21mm Tri-Elmar, and dubbed "Frankenfinder" by the Leica cognoscenti, this piece is available as a separate unit for those with a lot of wideangle lenses and more money than time to change finders along with changing lenses.

The view.  Clear.  Very, very clear.  Multicoating throughout, one aspheric element and one achromat make it just about the clearest accessory finder around.  There is some barrel distortion, but this finder covers 16mm on a film camera.  Did I mention that it is amazingly clear?   Magnification is about 0.3x.  This is quite a bit clearer than the 21-28mm Leica varifocal finder, although you have to take size into account.

The eyepiece.  Huge, rubberized, and capable of taking R diopters (the big round one).  Score!  On a Leica M camera, the eyepiece is directly over the lens; on a Hexar RF, it's slightly off to the right but close enough not to have too much parallax.  The point of view and wide angle of the finder sometimes allows you to see the lens's aperture ring - if not focus setting - through the finder.

The projected brightlines.   Illuminated by a separate window (a la the 65mm viewfinder for the Fuji G690), these are just like the ones on your M camera body.  The brightlines change size for various lenses: 16mm, 18mm, 21mm, 24mm and 28mm.  The framelines change position to match five parallax settings: 0.5m, 0.7m, 1m, 2m and infinity.  The framelines are dazzlingly bright and the framing is fairly conservative.

Meeting on the square and leaving on the level.  This is the most ingenious part.  The finder has an integrated bullseye spirit level that is visible below the frame.  Although it is not usable when the camera is in portrait orientation, it is invaluable in leveling the camera for handheld wideangle shots (although you need the steadiness of a target pistol shooter sometimes).  The level has a greenish glow-in-the-dark background that helps make it visible in poor light.  The level is fairly important because the barrel distortion of the framelines makes them challenging to use as a reference for leveling the camera.  There is nothing else like this on the market.

Size and construction.  This is not a toy.  The body appears to be black anodized aluminum.  The mounting foot is a substantial, screw-lock wheel that resembles the one you might find on a flash. All of this fits in a real leather case that could hold three rolls of 35mm film.  On an M camera, this pretty much takes up the top plate between the rewind knob and the shutter speed dial.  On an M8 or a Hexar RF, it lets you see the frame counter and the shutter speed dial.  It does allow you to see the exposure comp dial on the Hexar.

Weaknesses.  As a user, I think this item could have been designed slightly better.  I have three comments.  First, a spirit level should be visible in each orientation - not just landscape.  This would really help in portrait mode, where currently the only real way to level the camera is to match the bowing of straight lines in the subject to the bowing of the framelines.  Second, the spirit level should be illuminated by something other than glow-in-the-dark plastic.  Maybe a tritium tube like on high end watches or gun sights.  In fact, since this unit prevents the use of a flash, maybe the camera could provide a small amount of power through the flash shoe to light the level and the framelines.  Which brings me to my third question - why not pass through a TTL signal for a flash on something like a Nikon-style mini-DIN socket?

Perverse alternative uses.  Since this fits any camera that has (or can do) a 2:3 aspect ratio and has a standard ISO accessory shoe, you could easily adapt it to a medium format camera for wideangle use (see table above).  You could also use it on an SLR for mirror lockup wideangles and fisheyes.  Or to shoot infrared pictures where the filter blocks your view.  The most perverse single use I have found so far is on the Ricoh GR Digital II (which the Leica finder dwarfs).

Against the competition.  There are three basic types of competition for this finder (at least currently made).  The first category is made up of inexpensive Cosina Voigtlander, Ricoh, Sigma, and Epson finders.  The 15mm and 25mm CV finders have no framelines, which means you have to buy a double shoe and a spirit level to get straight pictures.  The other plastic fantastics are ok, but it's $169-200 a pop, five finders gets you to $845. 

The second category is the higher-end Leica and Zeiss single-focal-length finders.  These give a less distorted view.  And the clarity is excellent.  But for that kind of money, the parallax correction is basic (usually nothing more than a dotted line), and there generally is no locking mechanism, putting that very expensive bauble at the mercy of spring tension in your camera's accessory shoe.  But at a usual price around $400, these finders are not a great solution if you are living with an M8 and a 35mm rangefinder.  For example, if your main lens was a 21mm, you would need both a 21mm finder for the 35mm camera and a 28mm for the M8 (total $800).  And if you need a bubble level, you are out of luck.

The final category is not so much a category as a single finder, the Leica 21-24-28.  Barely a current item, and selling used for around $200, it is manufactured by Cosina, has solid metal construction, sports a locking mechanism, and features a zoom mechanism for framing.  There is no parallax correction and no brightlines, but eventually, you can get used to the black frame edges for lining things up.  This is by no means a complete solution, but it provides some ability to use the same lens on different bodies.

Conclusion.  Expensive, but not as difficult to justify as you would guess simply looking at the price.