Puzzled about process for micro focus tuning

[paul_heagen]

<p>I have read some articles and watched a YouTube video and am still baffled by one step in the process of calibrating the focus on lenses with my 50D.<br>

They all say to take several photos, starting with Live View. They then say use AF and take phones +10, zero or -10. Where do those numbers come from? <br>

Later it says to match the AF photo to the Live View.<br>

Huh? I'm really unclear on where on the camera this is getting done.<br>

Any help? Thanks!</p>

<p> </p>

[Marcus Ian]

<p>When I did this for my 50D (and this was a few years back), I didn't use LV at all.</p>

<p>All it took was printing out a scale target, propping it so it was ~45deg relative to the throat of the lens. Then setting up the camera on a tripod, and using one point (center point only) AF, focus on the zero mark (center of scale) on the target. Take a picture.<br /> review the image, zooming in to 10x to identify which mark on the target is perfectly focused, then adjust your point in the MFA menu, and take another picture, and repeat, until you have a setting which gives you images with the center of the target (or wherever you are aiming the center AF point) in perfect focus.</p>

<p>If you have trouble doing it all in camera (ie, seeing the perfectly focused spot), set it up for tethered shooting, and you'll have the monitor to help, although w/ a 45deg target, it's usually pretty obvious.</p>

<p>First time I did a 1/2 dozen lenses and it took about an hour or so. Especially important with fast primes, and don't forget to shoot WO.</p>

<p>To answer your specific concern, 'where' in the camera is in the phase detect autofocus system. Essentially what you are doing is telling the camera to shift the point it's aiming at towards or away from the camera (so it senses how far to focus the lens when shooting, and does so either a bit more or a bit less then it would otherwise do so (depending on your setting) - compensating for lenses that are consistently back or front focus -many, if not most, do whether we usually notice it or not). LV doesn't use phase detect on the 50D, just contrast, so it doesn't affect LV focusing in any way shape or form. </p>

[paul_heagen]

<p>I appreciate the response, but it points to the cognitive problem I am having -- I know the procedures to setup, but I don't know where this "adjustment" is. I know the Function setting to get to micro focus, but what exactly do I do to "adjust" the camera? </p>

<p>Uising your words: then adjust your point in the MFA menu, and take another picture, and repeat, until you have a setting which gives you images with the center of the target (or wherever you are aiming the center AF point) in perfect focus.</p>

<p>What do you mean adjust the pint and how do I know which way and how much to adjust?</p>

<p> </p>

[Marcus Ian]

<blockquote>

<p>but what exactly do I do to "adjust" the camera?</p>

</blockquote>

<p>C.Fn III -7<br>

1) you select whether or not you want this adjustment to apply only to this lens (the one you have mounted), or whether you want it to apply the same amount to any lens you have mounted.<br>

Usually the first is the preferred choice, as, more often, the amount varies by lens. - especially true for fast primes.<br>

2) you set an adjustment amount (- for Forward (away from camera), + for Backward (toward camera). so if your actual focus (point of most precise focus -in the image) is CLOSER to the camera than where your AF point indicates, you subtract from the adjustment (-). The 'amount' of each incremental adjustment point is dependent on the lens you are using, and varies by maximum aperture/ FL.</p>

<p>Obviously, you are kind of uncomfortable with this, but it's really actually pretty easy. I'd suggest pg 180 in your manual For all the relevant information. I'm not going to be able to do it for you - you've got the instructions, and you've got the principle of operation.... and, worst case is you totally screw it up, in which case a hard reset will wipe it all (or you can, with the trash can button)</p>

[phule]

Why do you feel you need to do

this in the first place?

[JDMvW]

<p>Rob- very much + 1</p>

<p>It should be necessary only if you are getting persistent front or back focus errors <em>not related to user practice</em>. </p>

<p>Otherwise, this sort of adjustment is completely covered by the "If it ain't broke, don't fix it" principle.</p>

[dan_south]

<p>Have someone show you how to do it - someone who already knows the procedure. If you adjust your camera incorrectly, the results will be worse than if you had not adjusted it at all.</p>

<p>The procedure isn't that difficult, but you have to do it properly. Either that, or just forget about it. It's probably not going to make a big difference on a 50D.</p>

[paul_heagen1]

<p>I guess I never saw anything that said to select "INFO" to get the slider bar to appear. that was my question about "how" to adjust the focus. <br>

While I'm on it, I did not notice any difference going as much as +-20 either way. Am I supposed to hit SET before I take each test picture?</p>