In-camera Cyanotype exposure calculator

 Ilford/Harman do a wonderful little print-at-home dial calculator for pinhole cameras - but it also covers the range of f/ stops for more conventional cameras. 

After some playing around, I have found that it can be adapted to cyanotype as well.

1/ On the ISO (middle) disk, locate the ISO .375 entry. Directly opposite it, write in "Cyanotype".

2/ On the Lighting/Shutter disk (the largest, bottom disk), write in "UV12" between the "->" and the full sun. Then "UV6" between the sun and the "19", and "UV3" between the 19 and the clouded sun.UV 15, for folks in places like Perth or Broome, roughly lines up with the ">" itself.

That's it! At UV12, and f/1, an exposure time of 30 minutes is given as the result, which is just about spot on for a properly exposed image after washing. The same lens at UV6 gives a 1 hour exposure - which is correct, given the UV Level scale is linear. 

Have fun!

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