The error can be different at different distances. Next are some random things I want to put out there before continuing with the actual micro focus adjustment. Yes………………very simplified explanation of focusing and what we are adjusting when we do a micro focus adjustment. Which in theory should have the lens actually focus at 10 feet 1/8 inch and the photo be in perfect focus. So now the camera knows that the lens will focus at 10 feet 1/8 inch when it says 10 feet, so it tells the lens to focus 9 feet 7/8 inch. We are measuring this error and programming into those algorithms the error for this lens. This lens error is what we are correcting for when we do a micro focus adjustment. In the first section we assumed the lens was perfect. Now, this has nothing to do with the first thing I discussed. The camera says focus to 10 feet and the lens moves to what it thinks is 10 feet but is actually 10 feet and 1/8 inch. But, I will confess to not having a good enough understanding in sensor design to speak with 100% certainty that there can be no error from the camera side of the EM1. With the EM1 its all on the same sensor, so any error in the camera is highly unlikely. This second part can also refer to the camera but really only applies to DSLR’s because they use a separate sensor for focus (error can be introduced if the sensors are not aligned properly). Wait…………….need to point something out here How much that error is will be different for each lens. Because every manufactured item has some tolerance for each piece, there will be error. When the camera says focus at 10 feet the lens will move to what it thinks is 10 feet. It is the gears and other mechanical things within the lens. The second part of the equation is actually physical. This is the downside of PDAF compared to CDAF, the upside being how fast it can change focus distance when in continuous autofocus because it doesn’t double check and it’s why it’s the preferred method of focusing for CAF. There is nothing we can do about this fluctuation in the distance the camera focuses. This first part is not what we are correcting for when we do a micro focus adjustment. But this difference will typically be within a specific range based in part on how good the algorithms are (plus the quality of the lens).Īfter writing the next part I realized I needed to come back up here and explain something a bit more. The first time it could focus at exactly 10 feet and the next time 10 feet and 1/8 of an inch. Just because of the nature of things and the algorithms companies develop that are not 100% perfect the camera will determine a slightly different distance each time. If you put a camera on a tripod and a target at lets say 10 feet and press the focus button, then defocus and press the focus button and then repeat this over and over…………….Įach and every time the camera focuses it will be at a slightly different distance.
The first is the fact that PDAF doesn’t focus to the same distance each and every time. There are two things to talk about concerning that question. Now…………why did I say “it focuses the lens to what it thinks is that distance”?
So, when it determines the distance using the phase differences….it focuses the lens to what it thinks is that distance. It knows based on the position of the lens elements at what distance the lens should be focused at. PDAF uses the difference between light phases from two points to determine distance to subject (it also uses it to determine direction and speed for CAF) and it moves the lens to that position. I don’t have the time or energy to go into a detailed explanation of either. Now…….before I go on I want to preface this with I am giving a very simplistic explanation of PDAF, as I did CDAF. Because it does this back and forth comparison it is very accurate, much more accurate than PDAF. When a camera focuses with CDAF it does this really fast back and forth focusing and from that determines focus by looking at contrast in the area covered by the autofocus point the user selected. Oh………also of note - when I describe how CDAF & PDAF work I am talking about SAF.īut………lets talk about CDAF for a second. I was asked if I would make a post about doing a micro focus adjustment on the EM1.īefore getting into doing the actual alignment I want to mention a few things about PDAF.
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