Bobkeenan Photography Micro Adjustment Auto Focus Calibration Techniques Compared
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The reason for this post on Micro Adjustment Auto Focus Calibration Techniques Compared is that a little over a year ago I wrote a post on Micro Adjustment Auto Focus Techniques . I have had several questions about how one compares to another. That previous post described some of the different technique but did not do a comparison for a specific set-up.
I am going to compare 5 techniques.
Compare Images of an organized scene for various MA settings
The Moire technique by Bart van der Wolf and explained well here
The Lens Align System
Focus Tune with Lens Align
Reikans FoCal
So about the setup. I am using a Canon 5D Mk III. The len is the sigma 50mm f1.4.
Canon recommends that you calibrate the micro adjustment at 50X the lens size. I find that is is too impractical and others have written and I have verified that 25X works fine. So for these tests I used the 25X or about 49″.
This could be anything but it should be set up so that you can see the depth of field movement as you change the MA. I used a set of batteries lined up on table. The battery in the center (green) was my focus point. The others were lined up along a 45 degree line to the plane of the camera sensor at regular intervals (about 1/2″) both forward and behind the center battery.
So I focus on the center battery and take 9 shots starting at an MA of -20 then -15,-10,-5,0,5, 10,15,and finally 20. I had the camera set up in manual with a 2 second delay, ISO of 100. So here are the shots that I got with this approach.
-20 -15 -10 -5
0 5 10 15
You can click on any of these images to see a larger view. What you will see is that the sharpest green battery is between an MA of 5 and 10. I could then take some more images from MA 5 to MA 10 to narrow it down. But for this exercise I know its between 5-10 and that is pretty close.
Note that I have seen setups with rulers or printed pages with rulers usually set at 45 degrees to the camera sensor plane but you have to make sure you have a good and that your angles are all about right.
I this method I set up the camera 49″ from the computer screen and bring up the moire pattern that can be found on the linked site. Then in manual mode I take pictures at MA -20,-15,-10,-5,0,5,10,15, and 20. Note that in all of these techniques I cycle the focus back to infinity. Here are the results of those images.
Again, You can click on any of these images to see a larger view. What you will see is that the strongest moire effect is happening around image +5 MA. But its kind of a weak effect for me to see (unless I did something wrong). I could then take some more images from MA 5 to MA 10 to narrow it down. But for this exercise I know its close to +5. But its a weak indicator and really does not give me a good idea of the depth of the DOF and where it begins and ends. But I can see it, in a non-quantitative way in the previous example.
This system is self aligning with the target and the camera. I take the images again at the 9 different MA values. Normally what I would do is watch the target using Canons EOS Utility . But for demonstrating this comparison the photos serve a better purpose.
So this is a lot more quantitative. I can see where the DOF is and how it moves with the MA. But one problem here is that this and all the previous are relying on one image per MA. And i have found, and you will see later, that AF bounces around a bit. So if you really want to be anal about it you should have several shots for each MA. But I do not have the patience for that. Anyhow in this example the MA should be some where between 0 and 5.
So LensAlign took out some of that tedious sampling with Focus Tune. What you do here is take shots at interval MA’s but take 3 shots for each MA and load them into their software. He is the resulting analysis.
So… somewhere between 5 and 10 on the MA.
Finally there is Reikans Focal. Again, I explained how this all worked in my previous blog. For this setup I used the 49″. And set the preferences to run a lot of points. My Canon 5D Mk III will not work on auto MA change so I have to change the MA in this example 9 times. Most everything else is automatic. Here is the result.
It says set 6 as the MA.
Conclusions
They all gave about the same answer. The battery set-up is FREE and if you are not anal like me it will work fine. The Moire method did not work so well. The difference was difficult to tell but it is free. The LensAlign system has the best visual clues for where you DOF is and how its changing. I think I like this the best but it fails in that you have to take a lot of samples to get the AF error averaged out. The Focus Tune is a nice addition and that will take that error out. Finally FoCal does it all and many other things like focal pt comparisons, AF repeatability, dust detection and other stuff. But you are totally relying on the software and the output graph and data. If you trust that stuff then this is the best. If not and you like to see the depth of you DOF then LensAlign with Focus Tune is the answer.
UPDATE
Someone suggested that I check out the AutoTune Method. Another FREE method. And I have to say this one is very clever. You should watch the video for specific instructions on how to do this. But all you need is your camera, a tripod, and a target. I used my lensalign target because it allows for me to make sure it is parallel to the camera sensor. Essentially you are setting up the camera to be fully focused on the target and then switching it to manual mode. You then cycle through the MA’s looking for the beep, red light, green dot, or whatever your camera says when you are in focus with a half depression of the shutter release button. So I set mine up at the 49 inches for my 50mm lens. Now that is 25X distance not the 50 x that this guy recommends (I will try it at 50x and see if that makes a difference). Anyhow I got an in focus reeding from MA’s that spanned -7 to +17. You pick the mid-point and …… You get 5! which is really the same as the other methods. This gets the award for the most clever, easiest and quickest but I still like to see the DOF in realtime. But… to each his own.
AF Microadjustment techniques compared March 7, 2013 […] comparing the techniques with one set-up. So I got bored and spent a day doing this. You can see it here : Bobkeenan Photography Micro Adjustment Auto Focus Calibration Techniques Compared Bottom line […] Reply
[…] comparing the techniques with one set-up. So I got bored and spent a day doing this. You can see it here : Bobkeenan Photography Micro Adjustment Auto Focus Calibration Techniques Compared Bottom line […]
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