In camera focus adjustment.
- Thread starter FiestaRed
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- Richard
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It's an electronic change.
The phase-detect AF system of DSLRs works off a simulated focal plane which detects sharp focus, and the calibration adjusts the alignment between that and the actual image on the sensor. How accurate that alignment is, ultimately depends on the tolerances in the lens focus and zoom mechanisms. They are rarely dead right throughout the full range and the final setting is always a (very slight) compromise.
Contrast-detect AF (eg live view, working off the actual sensor image) is not dependent on any lens tolerances.
The phase-detect AF system of DSLRs works off a simulated focal plane which detects sharp focus, and the calibration adjusts the alignment between that and the actual image on the sensor. How accurate that alignment is, ultimately depends on the tolerances in the lens focus and zoom mechanisms. They are rarely dead right throughout the full range and the final setting is always a (very slight) compromise.
Contrast-detect AF (eg live view, working off the actual sensor image) is not dependent on any lens tolerances.
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- Andy Drake
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Its a mostly pointless "feel good" marketing feature with limited real world use.
Firstly - its useless for zoom lenses as most are not par-focal. This means if for example, you have a 24-70 lens, and you focus at 24mm then zoom to 70m, you'll need to re-focus again at 70mm. Focusing isn't maintained when zooming so you can't tune these with one setting across the whole zoom range.
Thus for these type of zooms (and almost all zooms work this way) the + or - figure you dial in, is only applicable to one focal distance only for a non-parfocal zoom lens.
Always use manafacture warranty to sort out these issues not half-assed bandaids - if all lenses need tuning, the body needs to be adjusted. If a particularly lens needs a large offset then the lens needs to be re-caliberated.
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I agree it's largely a feel-good thing, and if you don't know what you're doing there's a good chance you'll make things worse with micro-adjust, but par-focal zooming hasn't got much to do with focusing method. If you change focal length you should refocus, regardless of whether you use normal AF, live-view AF, or manual focusing.
On a Canon camera with micro-adjust, there is one control for adjusting the focus of all lenses, which is effectively body adjust. And another control to tweak individual lenses. Between the two there is a lot of very fine adjustment, and is exactly what a manufacturer's service department would do anyway. It's not a half-assed bandaid.
And you can use it to adjust third party lenses, for example my 70-200 focuses slightly differently with a Kenko telecon. I suspect a manufacturer would charge for that, warranty or otherwise. Whether or not it actually makes any difference in practise is a moot point
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Only if you sent canon your camera and lens would they use the in camera micro adjust. As you are adjusting the camera not the lens.
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- Andy Drake
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Parfocal ness is eveything, and the reason fine tune only works well with prime lenses.
A zoom lens that was parfocal would also be tunable because you could guarantee, say a -10 offset would work from 24 to 70mm for example. As it is with focusing changing depending on zoom, you just can't dial in a one-size-fits-all zoom offset.
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All that micro-adjust is, is an interface that allows users to access the calibration adjustment that has previously been the preserve of service departments with bench equipment. The result is identical.
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No its not. Camera serving generally uses allen keys to align mirror box and AF sensors.
Its no substitute for proper servicing. Many cameras ie Nikon and Sony are user adjustable via allen keys.
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If you have to take a spanner to it, that's major-adjust, not micro-adjust.