Micro adjust that AF function if you can

[chauncey]

As a devout "pixel peeper", I want my AF to be "spot on". To that end, if your body allows it, this micro focus adjustment technique for correct AF, will work when you utilize "focus stacking".

For a target, I used a swatch of neon colored duct tape on a yardstick which was propped at an angle at an appropriate shooting distance.
Tripod mount the camera with a remote shutter with your viewfinder focusing point aimed at the duct tape...you will need to twist the focusing ring to OOF between shots to make the AF "hunt".
Take a series of images, each with a different micro focusing adjustment, it's easier if maintain them in order, like -3, -2,-1, 0, +1, +2, +3 then load them into layers in PS>select all>align layers>blend using the stack method.
If your lens was way OOF, back or front focusing, you may want to start with adjustments like -20, -10, 0, +10, +20 to get them in the ball park and then, fine tune them on a second series.

It then become a simple matter to select the correct adjustment number based on the produced masks on the associated image layer.

This method removes the subjective guesswork of "which number to use" based on eyesight alone...and advantage for us older folks.

[Stagecoach]

Chauncey,

Are you taking account of hysteresis and deadband affecting repeatability when undertaking your tests?

[chauncey]

Are you taking account of hysteresis and deadband affecting repeatability when undertaking your tests?

Are you jesting with me because I have no clue what you said.

[revi]

hysteresis: you'll get different results depending on whether you approach the final value from below or from above
deadband: restarting in the same direction is immediate, going in the opposite direction has a small 'dead' area where you think you are focusing, but nothing changes.

[Stagecoach]

Chauncey,

Certainly not jesting but just mentioning some of the fundamentals of which any electro mechanical control system is subject to which is often overlooked.

With your camera fixed and aimed at the same target your AF system will position your lens mechanically in different positions depending upon which direction it has mechanically travelled from and how far it has travelled. There is an area known as the deadband within which your AF control system causes the system to say to itself, OK, I'm near enough. This is necessary to stop hunting.

There are a number of things that also affect this repeatability factor such as, electronics design, temperature and mechanical friction.

This repeatability factor should be taken into account and assessed prior to any lens fine tuning.

Grahame

[jcuknz]

Perhaps one should put the camera OOF to infinity and close for each setting to reveal the problem.
Must admit in my ignorance I thought Grahame was pulling somebodies leg
Surely with stepping motors it is impossible to get a precise focus unless focus happens to agree with the motor.

[inkista]

Just me, but I'm too damn lazy to do all that work. Planning on using the upcoming MagicLantern dot-tune function, instead.



Basically, you start with the camera in manual focus mode, and you use liveview magnification and manual focus to get perfect focus on your target. Then you start the dot-tune function. It rolls through all the values, and tests whether or not the AF-confirm dot lights up. It does four passes (two in each direction) to narrow/weight the responses as accurately as possible, and then the mean value (they debated median, but decided on mean) of the best-weighted range is then set in the camera for that lens.

[chauncey]

This repeatability factor should be taken into account and assessed prior to any lens fine tuning.

Yes, I understand and, you're correct. Any manufacturing process is an accumulation of tolerances and sometime they balance out and sometimes they don't.
Regardless, I repeat things like this to check variability and, as was suggested, crank that lens OOF between shots.

Magic Lantern is not available for my body...c'est la vie

[Stagecoach]

Hi Chauncey,

I have not yet attempted to fine tune my AF for any lens basically because I have never had a reason to suspect it may be out. Some time ago when I participated on another forum the subject was debated in horendous depth and detail by far more members than those that seemed to be interested in actually producing photos. It got so deep that the impression given by some was that they were looking for inaccuracies of a few millimetres in AF.

I suppose it all comes down to how relative it is to what you shoot and apertures used. My neighbour opposite has an excellent long picket fence of which I can shoot at 45 degrees and have often thought about using this as a test target just to get a general idea if something is way out.

Grahame

[Glenn NK]

Further to Kathy's post\;

http://www.fredmiranda.com/forum/topic/1187247/0

It's also on the Nikon forum at FM.

Doesn't require Magic Lantern.

Glenn

[jcuknz]

Since the purpose of all this is to get the camera to focus where wwe decide it should be my position is, without all the labouriousd testing and hi-tec options, that accuracy comes from the size of the target area used to find focus. Most cameras hve quite large focus areas and in this respect I am slightly jealous of Kathy and her G3 becuase I had one and delighted in the tiny focus target area but gave it away for the exterior knobs of the GH2.
As Kathy is much more technically oriented than I am I would be interested in her comment, perhaps contrasting her G3 and her bigger camera she writes about from time to time?

[inkista]

Further to Kathy's post;

http://www.fredmiranda.com/forum/topic/1187247/0

It's also on the Nikon forum at FM.

Doesn't require Magic Lantern.

Well, sure, if you don't mind doing all the steps manually. That page is actually linked to from the ML forum's discussion in the first post, since it's just automating the dot-tune procedure that's being discussed. The main difference is that you have to do the four passes of all settings and register if the AF dot lights up yourself manually. That's about roughly 80 times you have to test the beep. Per lens. [grin]. You can see why the ML folks wanted to automate the process.

Most cameras hve quite large focus areas and in this respect I am slightly jealous of Kathy and her G3 becuase I had one and delighted in the tiny focus target area but gave it away for the exterior knobs of the GH2. ...

Actually, in most cameras, the AF point on the screen/viewfinder is far smaller than the actual AF area used on the PDAF sensors. You get a false sense of accuracy.

... As Kathy is much more technically oriented than I am I would be interested in her comment, perhaps contrasting her G3 and her bigger camera she writes about from time to time?

Honestly? The G3's AF system kinda sucks in comparison with my dSLRs. Particularly for tracking and in low light. It's slow. It hunts. It's far less accurate in low light, and if I'm shooting in lower light, I have far more AF near-misses where my Canons would hit it bang smack in the center. I cannot WAIT for PDAF to hit Panasonic MFT cameras, and I was utterly gutted when the GX7 was announced without it. The only way in which the G3's AF system is better than my Canon's is that the touchscreen interface makes selecting an AF point hecka easier than cycling through or using the joystick on my Canon's. But that gets trumped when that one AF point keeps hunting... and hunting... and hunting... Comic Cons's Ballroom 20 was hell this year. Completely missed shots that I KNOW I could've nailed with my 50D. Hell. Even my 5DMkII could've beat it.

In good light, the G3's autofocus system works, and it's faster than most P&S cameras, but it's still not a patch on my dSLRs. But since most of the time I'm shooting in a deliberate fashion (even with retakes), it's not that critical. But when I see a bird fly by... I gave up handling and IQ moving from my Canons to the G3 to go smaller and lighter. Most of the time, I don't notice, but occasionally, I curse like a sailor at it. There are a few rare times I find the G3 to be utterly demented.

And don't get me started on the flash system. Just don't. That's when I start spitting.

There are reasons I've kept my Canons.