How to properly calibrate a macro lens?

[IntrepidB]

I have here a 70D (allows micro focus adjustments) and a 100mm 2.8 macro (non-L).

I take a photo or a bug and it's slightly out of focus (very slightly, but makes a huge difference on macro shots). I take one of those images that look like a rules for focus calibration, open on my ipad, place the camera on a 45 degree angle and snap a shot. I notice that it's back focusing a little bit. Then I adjust the micro AF until I can nail the focus on that scale (adjustment number is around -5).

After that, I go back to bug and shoot an ant - the camera is front focusing, so I keep shooting the ant and adjusting the focus and once again I'm at the zero mark for micro AF adjustment.

Any suggestions to get this focus properly adjusted?

I don't have focusing problems with other lenses, so it's not the camera body.

 

[Overread]

Honestly I would set the micro AF adjustment as needed based upon the charts and leave it at that. Then when shooting in the field shift to manual focusing. AF is doing a lot better than it used to but its still limited when it comes to very close ranges where even a tiny bit out is a huge amount and where there are often many interrupting or confusing elements in the photo that might cause the AF to lock onto something a bit before or after the target - not to mention get stuck hunting if it misses the focus.

Manual focusing is where its at - set the focus point (magnification)and then rock back and forth - squeezing the trigger when the focus is just where you want it.

 

[sk66]

Sounds like it's simply the inaccuracy of phase detection AF combined with the incredibly thin DOF when shooting macro. It is also quite likely influenced (possibly caused) by slight movements by you after AF has locked... When shooting macro a slight wobble (camera shake) can be enough to throw off the point of focus.

Smaller apertures, Smaller subject (magnification/distance), Tripod, Live View (CDAF), MF, etc., etc... I'd leave the AFMA alone.

 

[IronMaskDuval]

Honestly I would set the micro AF adjustment as needed based upon the charts and leave it at that. Then when shooting in the field shift to manual focusing. AF is doing a lot better than it used to but its still limited when it comes to very close ranges where even a tiny bit out is a huge amount and where there are often many interrupting or confusing elements in the photo that might cause the AF to lock onto something a bit before or after the target - not to mention get stuck hunting if it misses the focus. Manual focusing is where its at - set the focus point (magnification)and then rock back and forth - squeezing the trigger when the focus is just where you want it.

Yep! This is what I've learned from overread and tirediron. I don't use af at all. Mf all the way

 

[JerryLove]

Is this an area where live-view and contrast-detection would be better at nailing focus?

 

[Derrel]

Wondering if the AF bracket's "seeing area" might be a bit larger than you realize, or if the AF bracket is simply too coarse an aiming device to get accurate focus on very small subjects.

There's also human body wobble if you're shooting bent-over and hand-held; when the actual depth of field is 1 to 3 millimeters, even a slight,slight body movement is enough to be greater than the depth of field. If the stable, tripod-mounted tests are accurate, but then hand-held field work is sketchy, well, the issue might be one with the operator and not the hardware.

 

[table1349]

Here is the fix. Set you camera on a tripod, set a target up say 6 to 10 feet away aperture around f8. Adjust you micro focus adjustment until the target is dead in focus.

Now for macro.....turn auto focus off. With such small DOF you need to manually focus moving the whole setup back and forth until you hit the focus you want on the bug in the spot you want.

 

[sk66]

Here is the fix. Set you camera on a tripod, set a target up say 6 to 10 feet away aperture around f8. Adjust you micro focus adjustment until the target is dead in focus.

Actually, that's not a very good suggestion/method. The most widely recommended methods suggest using 50x the FL for a distance and using the widest aperture because you are tuning for accuracy and a narrower DOF helps here.

Here's an easy/free/accurate way of doing AFMA...

 

[table1349]

Fair enough. My point was to manual focus for macro. Here is Canon's recommended method. http://www.learn.usa.canon.com/app/pdfs/quickguides/CDLC_Accurate_EOS_AF_QuickGuide.pdf

 

[Dao]

For bug shot, I also set the lens to Manual Focus and then manually focus it at 1:1. Have the light and center focus point ready, point at the subject and move the camera back and fro. When the focus indicator "beep", I take the shot. Repeat the process again. Sometimes I bump the ISO a little so that I can lower the flash power and that make the flash recycle faster.

So basically the process is ..... MF (1:1) -> pointing at the bug --> move the camera back and fro -> "Beep" - "Snap" -> "Beep" - "Snap" -> "Beep" - "Snap" ...