AFMA Explained

Jeff Harmon answers year old listener question from Improve Photography writer Aaron Taylor:

Here’s a Photo Taco episode if there ever was one: AF Microadjust/Fine Tune. Why do it? When to do it? How important? Is it obsessive or necessary? Use a Lenscal device or just something you print yourself?

Jeff talks about how autofocus micro adjustment (AFMA) is something specific to DSLR cameras, not needed and therefore not offered in mirrorless cameras. Not all DSLR cameras have the feature to do AFMA, but if it does then it is something worth doing – especially if you shoot portraits using narrow depth of field.

Jeff talked about an 11 point setup needed to do AFMA:

1. Set your shooting mode to aperture priority.
2. Set your aperture to the very widest setting (f/2.8, f/1.8, f/1.4).
3. Set ISO to 100.
4. Set the focus point to use the single, center focus point.
5. Set your focus mode to single shot on Canon, af-s on Nikon
6. Turn off image stabilization.
7. Good amount of light.
8. Use a tripod.
9. The camera needs to be as level with the target as you can make it.
10. The camera needs to be a specific distance from the target.
11. Set AFMA to 0.

Jeff outlines 3 methods or processes to doing AFMA that seem to have almost equal support in the photography community with fanboys for each one:

1. Ruler method – setting up a ruler target on a 45 degree angle and then shooting shots with different AFMA values set through the camera menu to find which one most consistently results with sharp focus right where the focus point was placed in the scene. You can use DIY targets here with a ruler or tape measure, but paid for targets simplify things and are nicer to use.
2. Software calibration. Tethering your computer to your computer you can have software figure out what AFMA value most consistently has sharp focus where the focus point is. The most popular of that software by what seemed on overwhelming majority is FoCal from Reiken.
3. Dot Tune method invented by Fred Miranda. Ingenious out of the box thinking that leverages a comparison between contrast detection autofocus and phase detection autofocus plus the focus confirmation lights that come on when a lens is in manual focus mode.

After using all three methods Jeff preferred the Dot Tune as a process with FoCal software coming in as a very close second. A distant third was the ruler method. He did the tests many times across his four lenses capable of wide open apertures and couldn’t find that one method was more accurate than another and unfortunately each method has fans of that method dead convinced it is the most accurate so it is hard to say if there is a meaningful difference in accuracy.

Links mentioned on the episode:

Photo Taco – Focus Points Explained: http://improvephotography.com/36979/photo-taco-focus-points-explained/
LensAlign MkII target: https://www.amazon.com/dp/B004G3PANY/ref=psdc_3109910011_t1_B0041L3JS4 http://amzn.to/2p8y0OW
Datacolor SpyderLensCal SLC100: https://www.amazon.com/gp/product/B0041L3JS4/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1 http://amzn.to/2p8wLzo
FoCal Target Distance Tool: http://www.reikan.co.uk/focalweb/index.php/online-tools/test-distance-target-size-calculator/
Michael Tapes Design LensAlign Distance Tool: http://michaeltapesdesign.com/lensalign.html
Fred Miranda Dot Tune: http://www.fredmiranda.com/forum/topic/1187247

Other Photo Taco Resources:

Vote for Jeff’s “Cull” module idea to be added to Lightroom: https://feedback.photoshop.com/photoshop_family/topics/less_redundancy_actions_during_import_into_lr_instant_rating_during_import

Podcast: Download (Duration: 42:54 — 39.4MB) | Embed

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