Aperture / DOF Scale (similar to Sinar F2)

**celtic9** · 9-Apr-2016, 09:13

Hello everyone,

I'm looking to equip my Arca Swiss Discovery with an aperture/DOF scale similar to the one the Sinar F2 comes equipped with.

Any ideas/tips how to go about it? I don't have an F2 on my hands, e.g. maybe someone has a prefabricated scale or something similar that could be attached to the rail?

Thanks for your help!

**Greg** · 9-Apr-2016, 09:29

http://www.largeformatphotography.info/dofknob/

**ic-racer** · 9-Apr-2016, 11:55

Sometimes just a marker on the knob is good enough on a field camera. To elaborate: A mark on the knob lets you find the 'middle' of the focus spread. This is more important than the actual focal spread distance. Why? 1) If you want to make sharp landscape pictures you won't be using large open apertures even if your focal spread is small. 2) If you have a large format enlarger, you may not want to stop to f256 either if the focal spread is very large. So you wind up using something like f22 (4x5) or f45 (8x10) anyway, no matter how the focal spread calculates to a specific aperture.

Put another way: An error in finding the middle of the focal spread is worse than an error finding the focal spread distance.

Put a third way: The calculation to relate focal spread distance to aperture is an estimate based on many non-fixed variables. The middle of the focal spread is an exact physical point that needs to be set with the same precision you used when you focused on the near and far points.