20 6 July 2019 I http://www.amateurphotographer.co.uk I subscribe 0330 333 1113
DOES A NEW LENS NEED TO BE CALIBRATED?
Technique AF MISTAKES
Manufacturing tolerances can result in a DSLR’s AF sensor and a lens
not being perfectly matched, which means that your subject isn’t as
sharp as you might expect. Thankfully, high-end cameras have a lens
calibration or AF Microadjustment feature that allows you to correct this
problem. The following steps show how the AF Microadjustment feature
works using a Canon EOS 5D Mark IV and a calibration target created
from a free template downloaded from the internet at http://www.squit.co.uk/
photo/fi les/FocusChart.pdf.4 Find AF Microadjustment
From the menu, select AF Microadjustment in
the AF options. Press Set and scroll down to
‘Adjust by lens’ before pressing the Info button
to access the options.
7 Set focus adjustment
Use the main dial to set the focus adjustment;
use a positive number to correct front focusing
and a negative one for back focusing. Press
Set followed by the Menu button.
2 Use the widest aperture
Set the widest aperture and put the centre
AF point over the chart focus marker before
focusing and taking a shot. Refocus again and
repeat until you have fi ve images.1 Set up your target
Assemble your calibration target and mount
your camera on a tripod at least 25x the focal
length of the lens away. Next, select mirror
lock-up mode.
5 Check lens serial number
Press the Info button again to check the lens
serial number. If necessary, use the Set button
and main dial to enter the correct number,
then select ‘OK’.8 Refi ne the calibration
Shoot the target again and examine the
images to assess the impact of the adjustment.
If necessary (it probably will be) repeat the
adjustment process to refi ne the calibration.3 Review the images
Open the images on your computer and
examine them at 100% on screen to see
whether the camera is focusing the lens in
front of or behind the intended target.6 Adjust focus point
You can adjust the focus point of the shortest
and longest focal lengths. Use the scroll dial to
select the focal length that you want to adjust,
and then press Set.9 Repeat for other lenses
If you’re calibrating a zoom lens, repeat the
adjustment process for the longest focal
length once you’ve got the focusing right
for the shortest focal length.