Drop bed adjustment to optimal f-stop table

[Shayok Mukhopadhyay]

I'm referring to the table in http://www.largeformatphotography.info/fstop.html which gives the optimal f-stop for a given focus spread (D). The following may be specific to the construction of Graflex cameras; I have a Speed Graphic. I've attached a millimeter scale along the rail to quickly read the focus spread in the field. However, with the bed dropped (twenty degrees), it seems to me that when the scale shows a spread of D, the actual focus spread on the front standard is D*cosine(20). [The standard simultaneously falls by D*sine(20)]. The table would have to be adjusted accordingly. Does this make sense?

-Shayok

[Kirk Keyes]

Yes, you are correct. You're now moving the front standard along the hypotenuse side of a right triangle when you drop the bed.