DotTune - Autofocus fine tuning method

2StepSteve · 21 Mar 2013 at 21:33

I only came across this method yesterday and thought I'd mention it here.

It's such a simple idea and I've found it to be very effective. It's so simple that it makes you wonder why it's taken this long for this method to come about. Simple, yet brilliant!

I've micro adjusted one of my lens using this method and it seems like a flawless method, far easier than comparing multiple shots. This method also confirmed that I need a +10 adjustment on my Sigma 35mm just as my angled tape measure shots also proved.

D.P. · 22 Mar 2013 at 00:18

That is pretty much what I do anyway. The trick is to get a good target and have a well aligned camera-to-target vector.

Skynet-T800 · 22 Mar 2013 at 20:51

Is it quiet common for lenses to be out?

My 50mm f1.4 is hard to get focus where I want it even with tripod?

Magic_x_uk · 23 Mar 2013 at 18:13

Something that I am not sure about though,
Does the Diopter adjustment on the viewfinder, not play a part in all this. I mean if you have it set wrong (not at 0 but in the + / - field) then focusing could also be off as well because of this, could it not?

Andy90 · 23 Mar 2013 at 19:54

Magic_x_uk said:
Something that I am not sure about though,
Does the Diopter adjustment on the viewfinder, not play a part in all this. I mean if you have it set wrong (not at 0 but in the + / - field) then focusing could also be off as well because of this, could it not?

No the dioptre adjustment on the viewfinder will not make a difference with this method, since it has no bearing on the focusing confirmation built into the camera. You are reliant on the Camera indicating 'perfect' focus not your eye.

Cameras use a method called Phase detection, you can read all about it at

http://en.wikipedia.org/wiki/Autofocus

The following link explains how the system works in a Canon camera. The second picture in the article shows the two paths that light takes within the body

http://www.the-digital-picture.com/Photography-Tips/Canon-EOS-DSLR-Autofocus-Explained.aspx

When light enters the lens, it hits the mirror, this is semi transparent, some of the light is directed up through the focusing screen and then through the pentaprism and out via the eyepiece.

Some of the light hits the mirror and is usually directed straight down into the bottom of the mirror box onto a sensor and it is this sensor that uses Phase detection to determine if something is in focus or not. In the video Nikon have little arrows to direct you to turn the lens in the appropriate direction whilst Canon just have a little round circle. When the image is in perfect focus (according to the camera) the round light will be steady and doesn't blink.

However if you are manually focusing, then yes the dioptre has to be set correctly to your eye, because if it is out it will make a difference on what you see as being in focus.