Canon AF Microadjust

[HawgTide]

I assume you Canon guys are doing the AF Microadjustments on your lenses. I've heard several ways to do it and wondered what you guys do. I was surprised at how much it varies from lens to lens. I have a Tamron 90mm prime f2.8 that is super sharp, but I had to adjust to +16 before it reached the optimum sharpness. What are your experiences?

[MN Shutterbug]

I haven't done a thing. If I was dissatisfied with the sharpness of my lens, I would see what I could do. At this point, there is no reason for me to mess around.

[HawgTide]

That was my thought for the first month that I had the 50D. After reading a discussion on it, they were saying it has a "backout" option so nothing would be changed if you wanted to back out. After trying it, it was really simple and made a good bit of difference. I could always see a very sharp (focus) image, but I wanted to make sure the focus was on what I focused on. For example, if I focused on the eyes of a subject, sometimes I would notice that the nose or ears might be more in focus than the eyelashes. Some subjects would not be noticeable, for example a tree or bush. By making those minor adjustments, it really seemed to make a difference in portraits.

Basically, how I did it was set the camera on a tripod, manual focus at the widest aperture. The adjustments go from -20 to +20. So I would find a good still subject (I used a book shelf with lots of books). Focus on one edge or word of a book. Shoot pics at -20, -15, -10, -5, 0, +5, +10, +15, +20. Take them to the PC, blow them up to find which one was focused on the spot the best. So for example, +10 was the sharpest of all those. Next I would shoot +5 +7 +9 +11 +13 +15. Take those and see which is sharpest. Then shoot a few more above and below that number in 1 step increments until it is narrowed down to the best setting. A good thing is that you can do this for each lens and it will remember each lens setting automatically. That +16 on my Tamron tells me that the focus was off a good bit.

[Dbl]

HawgTide,

You really do not want to use manual focus. Do you manual focus with the lens on the camera? If you use the Chuck Westfall method you want to manual focus on infinity, then using "one shot" focus let the lens autofocus. Take three shots each time manually focusing to infinity and allowing the camera to autofocus. Do this at 0. Now do the same three shots at -5 and +5. Compare your results. Normally one of the three shots will be the sharpest, use the sharpest of each of the three groups to compare them against each other.

By the way Canon Zoombrowser is great for this, you can select to compare three images side by side and then using the synchronizing button zoom into 100%. All three move in making it easy to pick the best one. You can now go back and do some tweaking of the microfocus settings if you need.

You need to use autofocus to see how well the camera body and lens work together. That may or may not be the same as manual focusing. Most of my lenses are really close. I have one Tamron the 28-75 f2.8 and that was off at +1, hardly worth setting.

[finnbay]

Great tutorial, Dan!

[HawgTide]

Thanks Dan. I haven't heard of that method. That's why I ask this question, to see how everyone else does it. After thinking about it, I did use the AF one shot. (duh, that would kind of take away the point of this )Thanks for catching that. It was a couple of months ago and was just trying to remember how I did it. I didn't focus on infinity though. The guy (who's I followed recommedation) said choose an "average" distance to subject.

[Dbl]

That's cool, sounds like you had a good plan. I've read use 50 times the focal length of the lens. For a 50mm lens, that would be 2.5 meters, or approximately 8.2 feet. A 200mm would be 10 meters or 32 feet. I just use a distance that I normally shoot the lens at. Seems to work well for the long lenses. The short one's I shoot closer so you can see the fine print on the test chart.

[HawgTide]

Is Canon the only maker that has this option/feature? The reason I tried this is that my first lens purchase with the 50D was the 24-105 F4 L series. I was not happy at all with the results and after about a week, I took it back thinking I had a bad copy. Only after that did I learn about the adjustment feature. I wish I would have tried this before I returned the lens. My new 70-200 f2.8 IS arrives today, so I'll have to give this method a shot this weekend. Thanks again for the input.