Canon And Interim Calibration
We thought we would post a few of the most commonly asked questions we receive from customers here at Cameracal. This one is Canon camera calibration specific and one we get asked a lot of the time.
What happens at mid-range focal lengths when calibrating a zoom with Canon cameras?
As you may or may not know, unlike Nikon, modern Canon DSLR models (Canon 7D Mk2, 5D Mk 4, 1DX Mk2 - ) allow for calculated Auto Focus Micro Adjustments to be added for either end of a zoom. For instance, for a Canon EF 100-400mm F4.5-5.6L IS II USM it is possible to add a calculated value for both 100mm and 400mm.
So what happens at the intermediate focal lengths you may ask, what does the camera do? Sigma and Tamron can be calibration through a succession of focal lengths. Does it only adjust the values at either end, or does it do anymore?
Canon Camera Calibration Tests
At Cameracal, inquisitive as we are decided to run some tests to find out. We recently had a customer come in to then studio who had recently come back from Brazil having taken his 7D Mk 2 + 100-400mm Mk2 to photograph some of the amazing wildlife. The calculated figures at the 100mm end was -6 but at the 400mm end it was +8. Quite a difference, but what about the interim focal lengths, what was the camera setting here?
From our exhaustive testing we were able to conclude that the camera does indeed do something with regards these interim focal lengths. As mentioned, Canon's AF Micro Adjustment Control allows for either end or in the case of the latest middle / high end models (Canon Eos 7D Mk2 upwards).
What does the camera do?
In this instance the camera attempts to calculate and applies interim values in a linear fashion.
In this instance the camera calculated the following interim values:
100mm as calculated using Reikan’s Focal software = -6
150mm as calculated using Canon’s linear fashion method = -3
200mm as calculated using Canon’s linear fashion method = -1
300mm as calculated using Canon’s linear fashion method = +4
400mm as calculated using Canon’s Reikan’s Focal software = +8
Does This Effect The Accuracy?
Is this linear method as accurate as calibrating each and every interim focal length
using Reikan’s Focal length? The answer, ultimately no.
The linear approach used by Canon is ultimately based on “guess work” and does not take into account possible lens optic displacement in a group of elements.
Results using Reikan Focal
On many occasions we have, when calibrating Sigma and Tamron lenses (using their Dock
/ Tap In consoles), tested this theory as in using Focal’s method against Canon’s linear
In many instances if not all, the individual calibration at interim focal lengths yields more
accurate results. Note in order to come up with this conclusion, we have run MULTIPLE
side by side tests.
A recent example of this was seen when calibrating a Tamron SP 24-70m F2.8 Di Vc G2 lens at 50mm the results were as follows:
24mm as calculated using Reikan’s Focal software = -2
35mm as calculated using Canon’s linear fashion method = -+1
50mm as calculated using Canon’s linear fashion method = +4
70mm as as calculated using Reikan’s Focal software +6
Results using Reikan Focal
35mm = -+3
50mm = +11
With the Sigma and Tamron dock service we indeed calibrate for multiple focal lengths
(Tamron ultimately allow for more focal lengths to be added than Sigma) and we have
found that manual focal length calibration is ultimately more accurate than the linear
method used by Canon.
Does this really matter?
Does the difference of 3 or 4 micro adjustments make a difference? Depending on the focal length YES! The longer the focal length the more noticeable the difference. So in essence when a customer asks “Is it worth paying for a dedicated Sigma /Tamron Dock calibration” the answer is over whelming YES.
Note, these interim linear calculations can only be seen when taking the shot in AI SERVO mode and playing back said image on the camera or in Canon’s DPP (Digital Professional Pro) software. Nikon’s recent announcement with regards the ability to support Wide and Tele adjustments with the new D780 will almost likely follow the same linear guess work, until
this is tested fully though this is an assumption.