In article ,
Whisky-dave wrote:

Focusing with a mirrorless

Cameras don't use the mirrors to focus the image,

slrs have a secondary mirror behind the main mirror for the
autofocus system to work, which has its own sensor.

mirrorless focus using the main sensor.

Really, when I focus my M3 I use the focusing ring on the lens for
manual focus.

whooooooosh.

Gone right over yuor head hasn;t it, why do they but IR markings on lenes
and this gose back well before mirrorless are yuo really climing that IR
light focussess differntly for mirrorless cameras ?

whoooooosh even higher.

plus, modern lenses don't have ir markers anymore.

So WTF has that got to do with it.
IR works in the same way it has done since the big bang
whether or not lenes have a mark on them is irrelivant.

what you fail to understand is that a mirrorless camera focuses off the
actual sensor, while slr has a *separate* focus module.

in other words, with mirrorless, what you see is what you get. lens
markings do not matter. different wavelengths do not matter. if it's in
focus in the viewfinder or on the rear display, it will be in focus on
the actual photo. always.

with an slr, the focus module is separate, using a secondary mirror
behind the main mirror to reflect light to the focus sensor module. it
is calibrated for visible light, so for infrared, either you adjust for
the difference (using lens markings) or the focus system needs to be
recalibrated for infrared.