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Pentax 645 28-45 Image Circle


Well-known member
While this lens is definitely a beast, coming in at 3.24 lbs, it does offer an interesting range of focal lengths for architectural photography. The 28-45 focal length does a nice job of filling the gap between the 24mm and 50mm tilt shift lenses.

The image circle isn't quite large enough to get much shift on medium format, but it does offer a reasonable amount of movements on FF. Since the Cambo Actus offers a Pentax lens mount that can control the aperture and this lens has a good IQ reputation I wanted to give it a try.

I didn't end up keeping this lens, but I thought these image circle images using the Actus might be helpful to others that are considering it. Here's what I did:
  • The lens was focused to infinity
  • Exposures were taken with an LCC plate mounted to the front via filter adapter.
  • To get the complete image circle in each of the attached images, 4 exposures were combined for each file:
    • 10mm left / 10mm up
    • 10mm right / 10mm up
    • 10mm left / 10mm down
    • 10mm right / 10mm down
  • The aperture was set to my best estimation of f/11. The Actus P645 lens plate has a 1-10 scale. I estimated f/11 by comparing exposures taken with this lens and another lens set at f/11.
  • The Actus lens plate was set at 5 when the exposures from both lenses matched.
  • The images are taken at each of the focal lengths marked on the lens and included in the filename: 28mm, 32mm, 35mm, 40mm, and 45mm.
You can see from the results that the image circle is smallest at 28mm and largest at 35mm.