AF point as capture trigger?

Started May 28, 2013 | Discussions thread
brightcolours Forum Pro • Posts: 15,883
4 ways to trap focus (3 with your 450D)
  1. Use a Sigma lens. Tape off its right most contact (with contacts at 6 o' clock). Trap focus will work at every aperture. (Well, I know it works with my 2005 Sigma).
  2. Use any other AF lens (canon, tamron). tape off the right most contact (with contacts at 6 o'clock). Trap focus will work only at wide open aperture (lens error otherwise).
  3. Use an MF lens with a chip which supports trap focus. Works wonderfully well (with lens relatively wide open obviously).
  4. Use magic lantern firmware (not on 450D). Not sure how well it works as I have never tried it.

I built an adapter myself for an M39 mount close up lens, with method 3. from above (gave it the electronics from a dead old Sigma lens). Now I use it to trap focus on any AF point with my 450D, to get focus precise with handheld OVF work, upto f5.6. The lens does not have any focussing functionality (fixed focus), so you can imagine how welcome trap focus is....

Center focus point, as you can see the focus trigger is very precise....

"top left" focus point, triggered on the ladybug... 2 image stiched

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