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DotTune: Autofocus fine tuning in under 5 minutes

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Published on Feb 18, 2013

Update 2/15/14: I have switched from the Bob Atkins focus chart described in the video to a new, cross-hatch target I created in PS. This new target produces much more consistent results. You can download the target at:
http://www.testcams.com/DotTune/Cross...

DotTune is a new method I've developed for fine-tuning the autofocus on your lenses. Unlike existing methods, with DotTune you don't need to take test photographs at multiple AF tune values to find the best tune value. Instead you focus once in Live View to establish critical focus, then use the focus confirmation dot within the viewfinder to find the range of AF tune values which provide a reliable focus confirmation, then simply select the midpoint of that range as your final and optimal AF tune value.

*** Important Update for Nikon Owners ***
After making this video it was discovered that on Nikon bodies the viewfinder focus confirmation range increases dramatically when the body or lens is changed from Autofocus (AF) to Manual Focus (MF). I believe this is becase Nikon wanted to make manual focusing easier and faster by increasing the range of focus that provides a confirmation. However for DotTune this behavior is undesirable because it increases the range of tune values, sometimes beyond the limits of the +20/-20 AF tune scale. Luckily there is an easy workaround, which I strongly advise Nikon owners to use:

For step 3, do not set your NIkon body or lens to MF. Instead, configure your body for "back-button" focusing. Back-button focusing means that the Autofocus will not be engaged by a half-press of the shutter, which will allow you to perform steps 4 and 5 while leaving the body+lens still set to AF. To configure back-button focusing, set the "AF Activation" option to "AF-ON only". For the D4/D800 this is setup option a4, for the D3/D3s/D700 it's option a5, and for D600 it's option f4 and D7000 option f5 (for D600/D7000 the AE-L/AF-L button will serve as the AF-ON button). Once you've configured back-button focusing, use only a half-press of the shutter in steps 4 and 5 - do not use the AF-ON button since that will engage the AF on the lens. After you've completed your DotTune you can return the camera back to normal shutter-button focusing if desired. Again, do not set the body or lens to MF as described in the video; doing so will increase the confirmed focus range and make DotTune potentially inaccurate.


Segment Links:
00:00 : What is DotTune?
00:51 : DotTune Quick Reference
01:56 : Step 1 - Set up your AF Target and Camera
03:08 : Step 2 - Establish critical focus in Live View
03:35 : Step 3 - Switch to MF (excl Nikon) and set AF Tune to 0
04:18 : Step 4 - Evaluating Viewfinder Focus Confirmation
07:54 : Step 5 - Cycle AF Tune values to find confirmed range
11:42 : Step 6 - Set final AF tune value to midpoint of range
12:51 : Additional Notes
15:02 : Sample DotTune session

Here is a link to the Bob Atkin's focus chart used in the video: http://www.bobatkins.com/photography/...

Here is a link to the DotTune Midpoint calculator used in the video: http://www.testcams.com/DotTune/CalcM...

Link to +/-20 confirmed range workaround (all bodies):
http://forums.dpreview.com/forums/pos...

Link to +/-20 confirmed range workaround (Nikon specific):
http://forums.dpreview.com/forums/pos...

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