350D AF Precision Tweak

[SpeedingSphere]

This is the way Canon repairs their AF problems 80% of the time. I remember reading somewhere that there was a way to tweak the autofocus of the 350D to its max precision, so I've decided to give it a go. Read carefully and thoroughly before beginning. Please read the disclaimer at the bottom.

Inside the shutter area, behind the mirror, is a small hex screw hole that you can turn to adjust the settings of the autofocus, to either make it focus infront, behind, or spot on. I've read that usually, the 350D is set to a slight back focus. I want to correct this.



The gray screw half way up the housing, very close to the curtain, is what we're after.

What you will need.

A subject that you can see contrasts in. one that you can set your middle AF point to an exact point on it, numerous times, without struggle. For my shots, my middle of the photo is the red bulb.
About 45 mins.
A CF Card reader.
Clean work space.
I'm not sure of the hex driver size, but a very small one.
A blower bulb to dust in between every adjustment.
AF Lens @ Wide Angle, about 28mm or close to that
A thumb to hold the mirror back(dont open shutter via *clean sensor mode*, it could close on you and damage the sensor)

Major note, in between every adjustment, blow out the shutter chamber area with the blower bulb. It is necessary to keep all dust out.

All shots are taken hand held, no IS, at 1/160 and f/8.0, ISO100 with a flash @ 28mm from about 5.5ft away

DO NOT RELY ON YOUR LCD TO SHOW SHARPNESS
Transfer all pictures to the PC one at a time to find the best clarity, and crop to a small area of a 100% crop of the picture that shows detail and contrasts. Keep record of all adjustments, adjust both clockwise and counter, you may have either back or front focus issues.

Here is a crop of my first test image, no fixes, no editing.



Here is a shot after tweaking my 350D with a quarter turn of the hex screw towards the base of the camera.(Looking into the camera, lens release pointed upwards, turn the screw clockwise)



Here is a shot after 1/2 turn of the screw as to the same turn settings in the last shot.



I found my best AF point within 3 turns, but your results may vary. Experiment with different turns in both clockwise and counter clockwise directions. Be sure to compare every shot with the beginning shot that you started with, and the shot that is currently the most improved over the first. When you feel you're sharp enough, give yourself a pat on the back.

As you can see, details come out, and words become less "fuzzy" and the image becomes clearer over all. This has helped me with my telephoto and astrophotos as well.

If you have unsteady hands, and dont know what you are doing, I wouldnt recommend you doing this as the shutter curtain is right within 5mm of the working area, and one slip could cost you a whole sensors cost in repairs. If you know what you are doing, this should be simple, but for people looking at this with no knowledge of what could happen, and how to prevent it, DO NOT ATTEMPT. I dont take responsibility for damages to your sensor.

I hope this was a tip to some. I hope that somebody will try this, other than myself. Give it a shot, i bet it will do you wonders if you are having a few fuzzy shots. Good luck!

[zrfraser]

I think a tripod would beneficial as well since you are hand holding it would be hard to keep your hands in the same spot everytime, and that little margin of moving could make this a little less precise. The camera should be as still as possible and as staionary as possible. Nice job of taking things into your own hands and fixing something that looks relatively easy.

Z

[SpeedingSphere]

but I think that with the fact that with 3 sucessive increments of adjusting the screw, the image became sharper and sharper per each turn, proves its ability to cure focus problems.

I was just posting this to try and help some people.

[JTcooper]

I was wonder if this task could be done with the 20D, and how would I know if it on front or rear focus. thanks so much for sharing your thought.

[SpeedingSphere]

set something you want to focus on, and 2 things infront and 2 behind. like pen markings. Hold the camera so that it looks like this:

(camera>) X X (Target) X X

at a 30 degree angle or so, so that when you AF, it will either focus on the back 2 objects, or the front 2 objects. questions?

[JTcooper]

thanks bud, I'll give its a try one day with mine 20D hope I don't mess it up

[Norfindel]

You could shoot a ruler at 45 degrees to the camera to determine where the focus really is.