I started working on a somewhat interesting project that involves taking duplicate images with both the 110mm Super Symmar XL (super sharp) and a 0.450mm pinhole and comparing them from an aesthetic point of view. For the most part I will be shooting the 110mm @ f/5.6 (wide open) as compared to the 0.450mm pinhole @ f/245. According to most pinhole calculators this pinhole should be optimum for the 110mm focal length.
To accomplish this project I have a Copal #1 shutter with a screw in adapter that holds the pinhole close to the shutter blades so as to be close to the nodal point of most lenses. The shutter is mounted on a lens board so that I can take the odd numbered sides of my 4x5 film holders with the 110 and then without moving or changing anything on the camera (a 4x5 Wisner Expedition) I can swap lens boards and duplicate the image on the even numbered sides of the film holders using the pinhole.
This past weekend I tried my first set of exposures. The subject was architectural (an old stone Masonic Temple). I processed the film last night and made an interesting discovery; aside from the expected differences in sharpness and depth of field there was a substantial difference in magification. I wasn't expecting this because the focal length didn't change and the pinhole was near the nodal point of the lens. The difference in magnification is roughly 20-25%. Can someone explain to me what is happening?
For what it is worth I will also mention that I was using extreme front rise to correct parallax in the building. The pinhole actually vignetted about 3/4" into the frame perhaps the image was being cut off by the rear of the shutter. This probably has nothing to do with the magnification issue but I am throwing it in anyway.