Preview: Calibration Check Test

FoCal 2 is just around the corner, and we wanted to show you another new feature which will be available – the Calibration Check Test.  This is designed to quickly and easily tell you if you need to calibrate your lens.

What’s the benefit?

The test in the screenshot you see above took 38 seconds to run to completion – so in around half a minute you can get an answer to whether you actually need to calibrate your lens.  And what’s more, once the camera is pointing at the target there is no manual intervention required for any cameras – even MSC mode cameras!

The marker on the coloured bar gives you an easy way to see whether you might want to calibrate your lens – in the example above we’re slipping from green into the yelow which is OK but could be better, so it would be worth calibrating this lens.  The test can even give an estimation of the AF Microadjustment required for the lens, showing a value of -5 above.

What’s more, because this test bases it’s results on image quality, it gives you a real-world answer to whether your lens needs calibration. As an example, your AF Microadjustment may need a change of 10 units, but if this only makes a tiny change to the overall image quality (as is the case with some cameras and lenses) then there really is no need to calibrate.

After the results above, we ran a Fully Automatic calibration on this camera and lens (Canon EOS 7D and Canon EF 70-200 f/4L IS), which set a value of -7 for the AF Microadjustment:

Then re-running the Calibration Check test gave us a 99% result with the marker well into the green – we can expect great image quality from autofocus with this lens now (note also that the Fully Automatic calibration gave us a result of -7 which isn’t far from the initial estimate of -5 in the first run of the Calibration Check test).

How does it work?

The test runs in 2 stages.  First, it builds a profile of the lens characteristics, finding out the best possible quality that can be achieved (which is then shown in the right hand cropped image).  It then tests the focus a number of times, comparing the results to the best possible quality.  The final result is a comparison between the representative focus quality and the best possible quality from the lens, which gives you an idea of how well calibrated your lens is.

The Results

The results panel of the test above shows the following information:

• Profile Quality – how well the lens was profiled during the first stage of the test.  A poor result here could be caused by serious camera vibration, light level changes or a damaged lens and would mean the whole test will be invalid.
• Focus IQ – this is the important value – it shows how closely the representative focus quality is compared to the peak.  A value of 100% would mean you’re getting the best quality from the focus system.
• Focus Spread – this shows how variable the focus is between shots.  A large number here (greater than about 25%) might indicate focusing problems and may reduce the overall quality of the result.
• Shift Error – this gives an idea of how far away from ideal the current calibration is (0% would be perfect calibration)
• Estimated Best AFMA – if the data is available (see below) this will give an idea of the best AF Microadjustment setting for your lens.

The coloured bar display shows some of the results visually:

• The side triangles and black line shows the Focus IQ
• The white “brackets” show the Focus Spread

Making use of uploaded data results

Back in FoCal 1.5, we started collecting data about the results of your tests (nothing to personally identify you, just a few numbers showing how cameras and lenses behave).  Using this data, we have compiled a series of profiles for each camera and lens and the Calibration Check test is the first test to make use of this aggregate data.  By comparing the profile data built during the Calibration Check test with the profile for your camera and lens in our big data set, we can make an estimate of the best AF Microadjustment setting for your camera!

It’s not perfect (which is why it’s shown as an estimate), but under most conditions it gets you a value within about 2 or 3 microadjustment steps.

So… When’s FoCal 2 coming?

We’re sorry it’s taking a while to get FoCal 2 out to you.  There have been a few distractions from it over the last few months as well as some complexity in implementing one or two parts of the system, but those are all out the way now and we’re steaming along with the final development.  We hope to have the first beta out for FoCal 2 by the end of July.

Comments? Suggestions?

If you’ve got any comments or suggestions about this new test then do let us know.  Now is the time that refinements can be incorporated, and if you like or dislike some aspects then we’ll take them on board as we finalise the test.

Let us know your thought in the comments below or through the Contact Form.