Do I need to calibrate autofocus?

We’re often asked whether there really is any point to calibrating your camera autofocus. Obviously we’re going to say a big, fat yes! otherwise FoCal wouldn’t exist, but I wanted to show a few charts to explain the sort of performance you’re likely to get “out the box”.

When FoCal is used to calibrate or analyse a lens, results are uploaded to our database which is then used to feed back into FoCal and give you an idea of how your camera and lens performs against other similar equipment.  But there’s an awful lot of data now – hundreds of millions of data points collected over more than 5 years – and this data can provide a valuable insight into how cameras and lenses perform.

Canon Cameras/Lenses

First, take a look at a histogram of the valid* calibration values calculated by FoCal across ALL supported Canon cameras and lenses:

AF Microadjustment Values for ALL Canon cameras and lenses
image-16565
AF Microadjustment Values for ALL Canon cameras and lenses

(* valid results are those which pass our internal criteria for being “sensible” results. We remove any results from tests which failed under odd circumstances, those who’s result calculation quality is not very good and various other reasons that might mean the data is not really representative).

So what does this chart show? It’s a count of the results at each microadjustment value – the higher the yellow bar, the more results at this microadjustment value. The actual number is unimportant (for these charts the most popular AF Microadjustment value will go up to 1.0) and we can see that the most popular AF Microadjustment result across all Canon cameras and lenses is zero, which is great!

The blue curve is a standard gaussian curve and we can see that the results fairly well mimic this.  The vertical blue line is the mean of all the results, and the red shaded area is one standard deviation which is a measure of the spread of the data.  About 70% of all the results are within the red area.

What does this mean in the real world? Well, it should mean that if you pick any (FoCal supported) Canon camera and then grab yourself 10 of the same lens type from your (impressive!) shelf, then 7 of those lenses should need a calibration value between about -5 and +5.  The other 3 are likely to need a calibration value outside of this range.

We generally say that it’s usually not worth sweating over 1 or 2 AF Microadjustment values, but 5 will make quite a difference to the quality of your captured image and the reliability of your autofocus. Which means even for the “good” 7 Canon mount lenses you took off the shelf, you can still get a fair quality improvement by calibrating, and for the other 3 you’ll definitely see a difference.

What about Nikon?

Here’s the same chart for all Nikon lenses:

AF Fine Tune Values for ALL Nikon cameras and lenses
image-16566
AF Fine Tune Values for ALL Nikon cameras and lenses

This one looks a bit different.  We still have a peak at an AF Fine Tune of zero which is good, but the standard deviation is quite a bit wider, and there are some significant numbers of cameras and lenses hanging around at those edge regions.

Again, taking our well stocked shelf analogy we’re now looking at 7 of those 10 Nikon mount lenses you picked up needing a value between about -11 and +10 which is a considerable adjustment.

So for Nikon, calibration is even more critical. 3 out of 10 Nikon mount lenses are likely to be very poor out of the box, and the other 7 will still require a potentially significant adjustment.

Summary

By combining millions of data points into these histograms, hopefully we’ve shown that it’s a really good idea to take advantage of the AF Microadjustment / AF Fine Tune feature of modern Canon and Nikon cameras.  Statistically, it’s almost certain that tuning your autofocus will improve your image quality, so fire up FoCal and get calibrating!

10 comments on “Do I need to calibrate autofocus?

  • Ralph Mastrangelo says:

    Indeed a convincing argument in favor of calibrating AF. However, how do we know that the results FoCal, or any other product or method, provides are accurate?

    I would like to see a follow up article that makes similar comparisons, but not between camera manufacturers. This one would be comparing calibration methods using various software and hardware devices.

    Reply
    • Hi Ralph,

      Good question, FoCal works by moving the lens to defocus and refocus multiple times and assessing the relative sharpness between captured images at different AF fine tune / microadjustment values. There are other ways to calibrate, Nikon for example has added an in camera calibration feature to it’s newest cameras (we did a direct comparison of the Nikon method and Reikan FoCal on the blog Nikon D500 Automatic AF Fine Tune )

      How you might go about assessing the absolute accuracy is more tricky. We believe FoCal provides the most accurate result of any available method, how you can prove that is harder to do! One thing we’ve worked on is checking AF calibration against the dual pixel data available in the Canon 5D4 – that is a fairly rigorous double check and in those cases we can ‘prove’ the result is accurate, information on the blog Bringing Dual Pixel Raw to Reikan FoCal

      Best Regards,
      Dave

      Reply
    • Hi Jon,

      The units across the bottom correspond to the available adjustment within the camera. On Nikon it’s called “AF fine tune” and on Canon it’s called “AF microadjustment”. Essentially the camera/lens can be calibrated within a range of -20 adjustment units to +20 adjustment units to allow for front/back focusing. There’s a good overview video linked in the FAQ that explains better Are there any FoCal calibration videos I can watch? 🙂

      Best Regards,
      Dave

      Reply
      • Jon Onstot says:

        I referred to the y axis, which runs vertically. Without units for both axes, a chart is meaningless.

        Reply
        • Hi Jon,

          Sorry, yes, the Y axis 🙂

          “So what does this chart show? It’s a count of the results at each microadjustment value – the higher the yellow bar, the more results at this microadjustment value. The actual number is unimportant (for these charts the most popular AF Microadjustment value will go up to 1.0) and we can see that the most popular AF Microadjustment result across all Canon cameras and lenses is zero, which is great!”

          Best Regards,
          Dave

          Reply
  • Dmitry Chastikov says:

    Is the more detailed info available on what are the cameras and lenses that fall into <-20 and +20 categories (essentially those that one can buy seriously defected). And those that come close to zero adjustments (that is those that are best in quality autofocus-wise)?

    Reply
    • Hi Dmitry,

      Great question, we wanted to present a very broad overview but there are differences between both lenses and camera bodies. I think it will need a more in-depth blog post (coming soon!) 🙂

      Best Regards,
      Dave

      Reply
  • When using longer lenses, 300, 400, 500 & 600 how will this work if you need it tethered? I would assume that I would calibrate my 600 at around normal focus distance @ 20 mrs

    Reply
    • Hi Steve.

      Yep, FoCal does generally require to be tethered (though it is possible to pre-capture images and FoCal can analyse them without needing to be tethered). With very long lenses it might mean using FoCal on a laptop outside depending. With 600mm lens we recommend a minimum target distance of around 12meters (approx 39 feet). See also What distance should I use for auto focus calibration?

      Best Regards,
      Dave

      Reply

Leave a Reply

Your email address will not be published. Required fields are marked *