lens calibration.What's it all about.??

-dave-m- wrote in post #16372541
You will need to micro adjust the lens again with the TC attached. The camera will store the adjustment settings separately.

Good to know... Cheers

Dear all, I'm calibrating one of my lenses for the first time and I'm using the SpyderLenscal. It all seems fairly straightforward and I found there are plenty of helpful guides around the web. However, a couple of things are not making sense to me.

Why does everyone recommend setting an equal amount of DOF in front and back of the focus point? Isn't any in focus area which is in front of the focus point just wasted? I can't think of many occasions when one would want to have anything in front of the focus point being in focus. I don't understand why people aren't recommending setting the larger part of the DOF behind the focus point? Isn't a bit more back focusing generally a good thing? What am I missing?

Plus, what about the one third, two thirds DOF rule? How does that fit in?

Best regards from Berlin, Germany

I might be wrong, but I think full on perfect focus is on a relatively narrow plane and the in focus DOF area before and behind that is just where focus is still acceptable in most cases. So you'd want to calibrate for perfect focus right in the middle of that 'in focus' field, because that's where the images is sharpest. Note too, I'm not sure if DOF is symmetrical around that perfect focus plane or not.

I've never adjusted any of my lenses, either I'm oddly lucky or I just don't see any problems with my lenses, and I have quite some.

Having just checked with an online depth of field calculator picking an 85mm lens at 1.4 on an FF body with a subject distance of 1 metre the foreground in focus and background in focus is bang on 50/50.
In fact all scenarios that I would use to calibrate lenses (maximum aperture, short distance to subject) bring in a ratio of exactly 50/50.

Only when stopping down and extending the distance to subject dramatically do you start to see a swing to more depth of in focus 'stuff' behind the subject than in front.
Ergo the method used to calibrate where correct focus is measured as being in the middle of a thin DOF is surely still the most accurate way.

I just calibrated my 85 1.4 on my camera and it was off by -15. It is so much sharper now. No wonder all my shots were off