Arca Swiss 2008 Photokina press release

[Emmanuel BIGLER]

A copy of the official Arca Swiss 2008 Photokina press release is here in pdf format:
(bi-lingual text in German & English)
http://www.cijoint.fr/cjlink.php?file=cj200809/cij06GtdvG.pdf

The Arca Swiss booth at the 2008 Photokina, thanks to Philippe Ossette (France) who visited the 2008 kina recently
http://cjoint.com/data/jChEQkA2Hz.htm

[Oren Grad]

Thanks, Emmanuel. The electronic rangefinder for the R is an interesting twist - shades of the short-lived accessory for the MT2000. Do you know anything more about how it's supposed to work?

[Emmanuel BIGLER]

The electronic rangefinder for the R is an interesting twist - shades of the short-lived accessory for the MT2000. Do you know anything more about how it's supposed to work?

Hello Oren !
I did not yet manipulate the system so I apologize for partial information here.
I know that Arca Swiss has considered several rangefinder principles in the development of the new R-line cameras (the 4x5" model, the RL3d is shown in the brochure)
Eventually they chose an ultrasonic rangefinder. The rangefinder gives you an actual distance to the subject that you convert into absolute graduations of displacements on the helical mount.
The conversion between absolute displacements of the helical and camera-to-subject distances is made through a kind of color-coded conversion table, no maths required, no palmtop, but I did not yet test the system !

The large diameter, fine-pitched helical combined to the factory registration of each lens allows the users of very short "digital" focal lengths to be sure of where infinity is, and from the infinity stop they can very precisely set their distance by rotating the helical. Exactly like in any old-style 'guess-focusing' camera with distances engraved on each lens, but here the built-in rangefinder (or an external rangefinder) gives you the distance.
Precisely setting the focus on a ground glass with "very" short focal lengths (say, below 45mm; 45 mm is not a short focal length for 35mm cameras !) is a challenge if you want to stay with the classical loupe & direct optical focusing. People using a digital back with the live-video mode can take advantage of the computer screeen as a combined magnifier and image intensifier, hence focusing is easier... if you are in the studio tethered to your computer.
Imagine that you go for the brand-new Rodenstock 23mm lens, the amount of travel required to move the right focus on the object side from infinity to one meter is only 0.5mm. You cannot properly set this without a very precise translation system, the helical is simply the way to go like for 35mm cameras.
From the infinity position, you set your distance as you wish either by yourself with any kind of rangefinder including a ruler tape ;) or with the aid of the built-in rangefinder by turning the helical by the proper amount.

Now if you want to use long focal lengths in macro, you'll need a long travel that may exceed the helical range, then you can transform the Rm3d into the front standard of a F-line, the Rm3d has a dovetail (no focusing gear, though, you'll focus at rear)) that slides directly on a classical rail and the Rm3d's rear attachment system is the classical 110 system common to lensboards and bellows.
If you have bougth a calibrated lens, you can also re-use it on any F-line camera by using a adaptor from 110 to the Rm3D's bayonet.

[Oren Grad]

That's very helpful, thanks. So it's uncoupled - read and transfer. Even allowing for a precisely-calibrated helical specific to each lens, I'm skeptical that would be adequate for critical work. Then again, to focus a lens like the new Rodenstock 23 properly the old-fashioned way, the ground glass register had better be *exactly* right.

[GPS]

...
Even allowing for a precisely-calibrated helical specific to each lens, I'm skeptical that would be adequate for critical work.
...

Have no doubts about the precision. The helical cylinder has plenty of space to mark the distance and the rangefinder is precise. You can get the same rangefinder precision on the helical ring if you want to. Do the math to see for yourself (what distance marks you need at what distance on the helical of a given diameter for different focal lengths and a different focus distance). It works. I have built a camera (paradoxically from an AS) on this principle even if with an optical/mechanical rangefinder. Works quickly and is precise.

[Oren Grad]

GPS, I'm not concerned about the precision of the helical, but rather the accuracy and precision of the rangefinder readout as well as the finesse allowed for transfer of the reading by the pitch of the helical.

[Emmanuel BIGLER]

So it's uncoupled - read and transfer.

Yes, exactly.

One question which will be raised sooner or later (the sooner it is raised here, the better ;) )..
.. is : the conversion table between focal lengths and graduations on the helical to compute the distances are probably tabulated for the "commercially available" focal lengths, e.g. 23, 24, 28, 35, 38,....
But what about the real focal lengths, e.g; 34.82mm for a 35mm ?
Well, the infinity stop is precisely set for each individual lens so there is no problem, but will the small difference between the "commercial" focal length and the actual focal length induce focusing errors ?

The problem appears to be exactly the same as the good old problem of the Linhof Technica for which you have an un-cammed lens and an orphane cam of the same "commercial" focal length.

The magic formula posted here
http://www.largeformatphotography.info/forum/showthread.php?t=40043&page=2
goes back to work ;)

For a lens of focal F1 precisely set at infinity but for which the distance is computed from lens travel according to another focal length F2, the error is acceptable as long as
abs(F2-F1) < c.N/(2M) ~ c.N.D/2F

where
"abs" means : absolute value of the difference i.e. the difference without the minus sign;
"c" is the circle of confusion that you consider as an acceptable sharpness in your mis-focused image;
"N" is the f-stop number;
"M" is the magnification ratio M = (image size)/(object size).
"F" ~= F1 ~=F2 the average value for F
"M" is used in the universal formula that yields the additional bellows extension "X" required to focus at a certain magnification "M" : X = M . F
An approximate value for M when the distance D to the object is much greater than the focal lengths is M ~= F/D (macro work is the typical situation where this approximation fails, of course !)

Here let's take an example with a 35mm lens used for objects located at one meter of distance, D=1000m to the camera; hence M~= 0.035;
Take a very stringent value of 20 microns for "c" this roughly corresponds to 50 cycles/mm in the image;
Take N=8, new digital lenses have their best f-stop around 5.6 or 8;

We get : |F2-F1| < approx. 2 mm.
I have no idea of the actual dispersion in focal lengths for top-notch 35mm "digital" view camera lenses, but I doubt that the interval of tolerance could exceed 2mm for a 35mm (??)

So probably we are safe to compute the conversion between the helical travel and the distance for a rounded "commercial" focal length as soon as the flange focal distance is set with the highest precision for each lens.

Do the math .... It works
This is my feeling, too ! ;)

[GPS]

GPS, I'm not concerned about the precision of the helical, but rather the accuracy and precision of the rangefinder readout as well as the finesse allowed for transfer of the reading by the pitch of the helical.

And that's what I was speaking about. Sorry you didn't get it.

[GPS]

So it's uncoupled - read and transfer.

Yes, exactly.

.....


Do the math .... It works
This is my feeling, too ! ;)

But of course!;)

[Gordon Moat]

There is also the other error with an uncoupled rangefinder, in that you lift the camera to your eye, check the composition and then drop the camera down to re-adjust. When you bring the camera back up to your eye to take the shot, how much have you moved?

If it was on a tripod, then I doubt there is much problem. DoF might cover up a few mistakes, and calibration can also help. Somehow ALPA seems to be doing fine with wide lenses and guess focus, so adding a rangefinder should be even better.

Ciao!

Gordon Moat Photography (http://www.gordonmoat.com)

[Emmanuel BIGLER]

Somehow ALPA seems to be doing fine with wide lenses and guess focus, so adding a rangefinder should be even better.

Yes, Gordon. I know personnaly two French photographers who use the Alpa 12 hand-held regularly. They do not complain against guess focusing.
I know a 3-rd French photographer doing mostly architecture shots, he is one of the first French owners of the Rm3D, he uses the camera on a tripod like any view camera he had used before in LF on film. Incidentally, thanks to him I was able to handle the new 28mm Rodenstock "digital" which is a strange beast with a strange shape; however the lens seems to meet the expectations of its owner.

According to his (somewhat fresh) experience, for him the helical solves the question of being absolutely sure of the infinity setting with short focal lengths e.g. the 28. He sometimes adds a tiny amount of tilt to increase apparent DOF according to the Good Old Rules. Really tiny ! my guess is: not more than one degree, may be half a degree !

[Emmanuel BIGLER]

You can see pictures of the Rm3d and RL3d (not forgetting the 8x10" misura) at the beginning of this recent Photokina report by Thierry Rebours :
http://www.galerie-photo.com/photokina-2008.html

Plus many other images of interest from Alpa, Linhof, Sinar, Silvestri, Cambo... the "niche" of technical view cameras for digital capture is growing !

[more photography]

A copy of the official Arca Swiss 2008 Photokina press release is here in pdf format:
(bi-lingual text in German & English)
http://www.cijoint.fr/cjlink.php?file=cj200809/cij06GtdvG.pdf

The Arca Swiss booth at the 2008 Photokina, thanks to Philippe Ossette (France) who visited the 2008 kina recently
http://cjoint.com/data/jChEQkA2Hz.htm

Emmanel

Having had a look at the new Raca M-line 2, what is the difference between this and and the old version. Ars the carriers the same, what about front and back standards. From the picture I can't see anty difference.