Jump to content

Brian Caldwell

  • Posts

  • Joined

  • Last visited

Everything posted by Brian Caldwell

  1.   Using a DX lens on m43 via the 0.71x Speed Booster shows about 7% more image circle diameter than using the non-boosted lens on a DX camera.  In most cases this has little or no effect on image quality - you just get a little wider field than normal.  Note that if you shoot video the top and bottom of the image are cropped, so this effect goes away.   Did you use a hood with your 30/1.4?  The only time I've seen such pronounced vignetting with a DX lens on m43 is with ultra-wide lenses having fixed hoods.  FWIW, I've tried the new version of the Sigma 30/1.4 on the Speed Booster, and it doesn't behave this way at all, even with the hood attached and stopped-down to minimum aperture.
  2.   The horizontal dimension of DX and BMCC frames is 23.6mm and 15.81mm, respectively.  So the horizontal crop factor would be:   (23.6)(.71)/15.81 = 1.06     If you calculate it based on the diagonals (28.4mm and 18.133mm, respectively for DX and BMCC) you get:   (28.4)(0.71)/18.133 = 1.11   Either way, you wind up cropping just a small portion of the DX format image circle.   On the other hand, if you mean crop factor relative to full-frame (24mm x 36mm) format based on the horizontal you would get:   (36/15.81)(0.71) = 1.62
  • Create New...