The Brainbox


an aid to focus


Arca Swiss Brainbox

Trigger retracted



Arca Swiss Brainbox

Trigger fully extented



Arca Swiss Brainbox

Trigger in a work position.

Here, one can read a 17.2 mm travel between two positions : (1) zeroed when the far distance subject was in focus (2) and then when the camera has been focused on the nearest subject.   In the window, the index shows the convenient diaphragm, depending on the size of the film and on the magnification.

The Brainbox had been discontinued. I presume that a model with the range in inches was also afforded.



  • Determination of aperture and focusing point

1. Move the Brainbox to the rear end of the optical rail with the locking knob positioned on the right hand side. Focus to the near point.

2. Drive the Brainbox to the rear function carrier until you have contact with it. Move the knob on the right hand side of the Brainbox downwards and, still holding the knob, focus to the far point.

3. The reading for the correct aperture appertaining to the depth of field for your format and degree of magnification can now be taken (¼ or ∞).

4. Take the reading for the extension factor on the right hand side of the brainbox and focus to the middle of the two focusing points (i.e. half the extension).

5. The sensor is re-locked by reversing the Brainbox back to the near focusing point.

  • Determination of the tilt angle for the camera back

1. Cut the template supplied to fit your camera format and trace the square to the groundglass with a waterproof pen. The centre of the groundglass is the reticule.

2. Instead of focusing to the near and far points, focus now to the newly marked H-base lines (57mm or 114mm). The top line corresponds to the near point, the bottom line relates to the far point. Proceed as described above. The extension factor shown on the right of the Brainbox, will result in the following swing/tilt ratios:
Base line 57mm: (format: 6x9cm - 4x5") 1mm = 1.0°
Base line 114mm: (format: 5x7" - 8x10") 1mm = 0.5°
The sensor is re-locked by reversing the Brainbox back to the near focusing point.

Please note: According to Th. Scheimpflug's principle, the tilt and swing angle are not identical for the rear and front standard and can therefore not be translated

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texte de : <Dominique Césari>
Dernière mise à jour : 30 mai 2009