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Today's theme is distance, scale and DOF. After having downloaded a super free application called iSee4K for the iPhone which lets me calculate DOF on the go, I thought I might apply it. So for this set-up, I calculated my height, divided it by the length of the sensor and multiplied it by the focal length of the lens to determine that I would need to stand 5 meters from the (estimated*) central nodal point of the lens in order to fit in frame at a 100mm focal length, and then further calculated that at f/2.8 I would have around 20cm focus either side of me, which is more than sufficient to keep me in focus but also give the background some blurring. I then set the ISO to 50 and bounced an off-camera 580 EXii at half power off the ceiling about two-thirds of the distance from the camera to me. And it worked – hence the smug, but slightly tired look!

 

Wanted to shoot this at 135mm, but my house just wasn't big enough.

 

* As my 100mm is a 1:1 macro, this was a fairly easy task. Simply measure the closest focus distance from the focal plane mark (sic) and then measure 100mm back from there. Ipso facto. This may have no scientific grounding.

 

365.restall.org

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Taken on July 24, 2009