Idea Suggestion: AutoFocus calibration

Started by BlueToast, September 01, 2012, 04:24:14 AM

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BlueToast

It would be handy and cool to have a feature where you can have ML apply a +/- step offset to the autofocus after the camera has finished its autofocus on a half-press.

I have a Sigma 70-200mm f/2.8 lens. Here is an example of doing autofocus while at 70mm: https://secure.flickr.com/photos/joyunbound/7892052264/sizes/l/in/photostream/

Here is another example where I zoomed in to 200mm, halfpress for autofocus, wait for autofocus to finish, zoom back out to 70mm, and full press from half press: https://secure.flickr.com/photos/joyunbound/7892047846/sizes/l/in/photostream/

Notice how much sharper the second one is because I zoomed in to the max to attain an autofocus value and then zoomed out. I think this is simply because of optics, but I could be wrong. At least for guys like me who have a low-end Canon t3i DSLR, it would be cool to figure out what +/- stepping works best so that I don't have to zoom in --> autofocus --> zoom out --> take shot.

I imagine the flow would work like this: camera attempts to autofocus by itself, and once it attains and establishes itself on a particular focus stepping ML jumps in and adjusts it +/- number of steps (something set by me in ML menus).

EDIT: This could also be handy in some situations where you're behind a transparent curtain and may either be video recording or using AI Servo to constantly autofocus. If you know the distance of your subject beyond the curtain or blocking object, you could have ML jump your focus away from you (applied post-autofocus). This way if you're moving slightly forward or backward from behind said partial obstruction, it would for the most part keep the focus at the particular distance you want it to be focused at. Donno, just a crazy idea.

Alia5

My T3i has the same "Problem".
I also believe this is an optics thing...

Bit i don't know if a simple offset would work, for every focus distance.

But maybe worth a try

So +1

Francis

Not possible, as listed under the stickied Not Possible thread. ML only has control over the focus motors in liveview, where contrast-detection autofocus is used.

The phase detection method, used in photo mode, can be off by a specific amount if miscalibrated because it uses a specific sensor array . This is why higher end DSLRs have this feature, AF micro-adjustment. Contrast detection AF is never off by a specific amount all the time because it is just going by what is read from the regular image sensor through the liveview routines and it is usually just off.

No idea about those new hybrid AF arrays though.

Also moving to Feature Requests and closing.

nanomad

EOS 1100D | EOS 650 (No, I didn't forget the D) | Ye Olde Canon EF Lenses ('87): 50 f/1.8 - 28 f/2.8 - 70-210 f/4 | EF-S 18-55 f/3.5-5.6 | Metz 36 AF-5