I'm quoted rather extensively in that piece so feel duty-bound to comment.
SLIDING BACKS
If you don't trust sliding backs (I didn't) then try the following:
1) Set the back to live view mode hooked up to a computer,
2) Focus it on a test scale like the Lens-Align one, getting the shot pin sharp with the lens wide open on the computer screen,
3) Slide the back backwards and forwards with the sliding back,
4) Look at the focus on the screen, (shoot if you like),
5) Check if you are sharp at exactly the point on the scale that was originally focused,
6) Repeat with different lenses
We did this with a well-worn, rental Arca Rotaslide and two different P65 backs. It was sharp every time with every lens (including the Rodenstock 40mm at F4). I didn't like the feel of play in it one bit but this didn't actually impinge on sharpness. The Alpa argument might sound impressive in principle but this experiment proves it false. I then went on to shoot 3-9 part stitched shots in several different countries in very difficult conditions and not one frame of one stitch had lost focus. This included shooting in pouring rain in the middle of the night with the camera perched right up on the top of a Gitzo 5561. (I was using my M-line and it was a bloody nightmare to focus in the first place but that's a discussion for later in the story...). Alpa are just wrong about this.
The second point is this, the major reason I want a sliding back is to compose on the ground glass. I love composing on ground glass, I've done it for years with film and I think for certain purposes it makes you take a better photograph, or at the very least, a different kind of photograph to anything you get from even the most beautiful of prism viewfinders. This is true of architectural photography in particular but also many other areas. Additionally, you really need a ground glass to compose and stitch. In my opinion, that's why stitched 35mm shots generally look so boringly composed (because they weren't, the camera was just pointed towards something that looked nice).
And of course with Alpa we aren't talking about a beautiful H4 or D3 prism viewfinder but something infinitely worse. Have you tried looking through the Alpa rangefinder? I mean really...it's a bad joke, a thing like that is way more of an obstruction to good pictures than, say, whether you shoot with the very sharpest lenses or the latest back. Grotesque distortion, incredibly vague composition etc. etc. and to be fair, the Arca one is only slightly better.
FOCUS
I went and saw Alpa, Sinar and Arca at the end of last year. All very impressive in their different ways but it seemed to me that only Arca had looked at the totality and really addressed the fundamental problem of achieving accurate focus: no ground glass can resolve sufficiently to accurately focus a high-end digital back. Ground glass is very low resolving, I've heard quoted 1-6 lp/mm. You can grind it finer but then it will transmit too much light through, you lose light intensity on the glass and your eye resolution drops because the pupil enlarges. It doesn't matter the power of your lupe or how fancy you get with your fresnel, ground glass isn't going to get you to the level of precision required. So you compose on the ground glass and move to a laser distance finder for really accurate focus. But then you are faced with the fact that the Rodenstock and Schneider helical mounts are ludicrously approximate items developed in the analogue age.
This is why the Arca RM3D and the RL3D is the right sort of answer to an absolutely crucial question. I just don't know how well it works in practise.
Where Alpa are absolutely right is that tablet computers, dedicated digital viewers etc. if realised properly, really could be the way forward. They also make beautiful cameras and have been very noble in offering for free their impressive looking distortion correction software (which I've admittedly only just downloaded).
