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.
First, take a look at a histogram of the valid* calibration values calculated by FoCal across ALL supported 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:
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.
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!