Fixing the Issue
We’ve looked a little at how the AF System works on a DSLR and the sort of things that can cause problems with your focus.
Let’s go back to our previous example of taking a shot, but this time, introduce a bit of a problem by moving the AF Module a little from where it should be:
This time, instead of getting a measurement of +27, we get +30. This goes into the AF Processor, which uses the calibration information among other things to determine that the lens should be moved 93 steps – remember, with the AF Module in the right place we needed 85 steps.
The lens is moved, the shot is taken, and you look at the screen, a little disappointed by the blurry result.
So what can you do about it?
Enter Focus Adjustment – AF Microadjustment on Canon cameras, AF Fine-tune on Nikon cameras.
This is a value you can enter into the camera which adjusts the result calculated by the AF Processor by a small, fixed amount, therefore correcting fixed issues with the whole Autofocus System!
Back to our example:
The AF Module is still in the “wrong” place, the AF Processor still determines that we need 93 steps of lens movement to get the image in focus.
But this time, we’ve set a focus adjustment value set in the camera. This causes the 93 steps to be changed back to the correct value of 85 steps – the lens moves to the correct position, and you get yourself a superbly focused shot!
How do you determine the Focus Adjustment value?
Ah… now you’re asking.
Have you heard of some software called Reikan FoCal? 😉 If not, then take a look here.
I don’t want to turn this article into a sales pitch. I’m rubbish at marketing and promotion, and I much prefer to put out some useful information and hope that people might share it, and those who can benefit from FoCal will get to learn about it. But I am going to say a few things about it here…
FoCal is designed to take the guesswork out of picking your AF Microadjustment / AF Fine-tune value by automating the process. Connect your camera to your computer (or Android/iOS device), and FoCal takes automatic control of your camera.
It takes a series of shots of a special target, builds sharpness profiles for the attached lens, and calculates the adjustment values you’ll need to tune your lens with your camera and get the very best shots.
FoCal can calibrate at the touch of a button but also shows you all its workings with graphs and detailed information if you want to dig into the details.
There are loads of other features in the Pro version, including real-world comparisons of your kit with typical results from other users and lots of analysis tools.
Check for free!
FoCal runs on Windows and Mac, but there’s also a mobile version, inventively called FoCal Mobile. And you can download it for free to your Android or iOS device, connect to your camera and check out the state of your autofocus system.
You’ve got nothing to lose – you might as well give it a go and see if you could benefit from calibration!
Cards on the table – you will have to pay to actually use FoCal to tune your camera and lenses, but we think that the benefit you get from FoCal makes it worth it. After all, you’ve invested hundreds or thousands of pounds/dollars/euros in your kit – it would be a shame to not be getting the very best from it.
FoCal Mobile Pro allows you to calibrate your lenses, and FoCal Desktop Pro lets you do even more:
- Full, automatic calibration with detailed results
- Comparison of your kit performance with 1,000s of other users of the same kit
- Autofocus Consistency testing
- Aperture Sharpness testing
- Full 2D Focus/Aperture analysis with MultiTest
- Quantify your Stabilisation System performance – both in-body and lens
- Automatic Visual Dust Analysis
- Review of historical data
- Camera configuration save/restore with Snapshots (Nikon only)
And more… the full feature list lets you dig around a bit more to see what’s on offer.
Enough of me shouting about how great FoCal is!
We now understand the problems that can occur with DSLR autofocus, and know we can use Reikan FoCal to fix it, but do you really need to bother?
The answer is an absolutely resounding YES! And next, I’ll prove it…