p.6 #3 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes
Just like to thank snapsy for this. It's a simple method that any engineer should be able to think of, but have never thought about. I'm excited to try this out.
p.6 #8 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes
So out of curiosity how does this work with a zoom lens? For example I ran this test with a 24-70mm lens with the following results:
@24mm: -3 to +7 => +2
@50mm: -3 to +4 => -1.5
@70mm: -5 to +8 => +1.5
If you average the three together, you're looking at a +.67 adjustment. So round up to +1 and that's the proper adjustment, or should the adjustment ideally be the same at any focal length of the zoom lens and the lens should be calibrated by the manufacturer?
p.6 #10 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes
I don't understand why micro focus adjustment is so popular. I have two bodies and nine lenses and have been shooting for years and I have never noticed an issue that could be solved by MA. And I often shoot wide open where focus is rather important. I suspect that many (most?) people are brainwashed into believing they might need it even though they have no evidence that it is really needed. Somebody needs to do a poll to see how many people actually get positive benefits from MA.
TTLKurtis wrote:
So out of curiosity how does this work with a zoom lens? For example I ran this test with a 24-70mm lens with the following results:
@24mm: -3 to +7 => +2
@50mm: -3 to +4 => -1.5
@70mm: -5 to +8 => +1.5
If you average the three together, you're looking at a +.67 adjustment. So round up to +1 and that's the proper adjustment, or should the adjustment ideally be the same at any focal length of the zoom lens and the lens should be calibrated by the manufacturer?
TTLKurtis, I think you need to lay off the KoolAid and go back to shooting. I'm pretty certain that plus or minus 1 on the MA is well within the margin of error. I bet you could set it to +/- 4 and not notice a real-world difference.
p.6 #11 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes
leftcoastlefty wrote:
I don't understand why micro focus adjustment is so popular. I have two bodies and nine lenses and have been shooting for years and I have never noticed an issue that could be solved by MA. And I often shoot wide open where focus is rather important. I suspect that many (most?) people are brainwashed into believing they might need it even though they have no evidence that it is really needed. Somebody needs to do a poll to see how many people actually get positive benefits from MA.
TTLKurtis, I think you need to lay off the KoolAid and go back to shooting. I'm pretty certain that plus or minus 1 on the MA is well within the margin of error. I bet you could set it to +/- 4 and not notice a real-world difference.
Haha, yeah I know that such a minor adjustment isn't going to matter much in the real-world. I'm more-so asking out of curiosity. I've never been a fan of KoolAid myself.
p.6 #13 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes
snapsy wrote:
So it sounds like the lens has an internal database of offsets which the camera can use to bias the PD sensing mechanism to account for positional-specific lens aberrations that would otherwise produce incorrect PD sensing.
Exactly. I think of MA as a BFCV which is specific to the combination of an individual lens with an individual body (stored in the body). Or you can think of BFCV as a microadjustment which is specific to an individual lens with respect to a reference body (stored in the lens).
What I'm not sure about yet is whether BFCV is an array (indexed by focus position), or a table (indexed by...?). I'm working on getting that information.
snapsy wrote:
I imagine the lens could also use the database to offset mechanical nonlinearities in the AF motor/servo.
Yeah, maybe. It might help with speed, to cut down the number of iterations.
p.6 #14 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes
TTLKurtis wrote:
So out of curiosity how does this work with a zoom lens? For example I ran this test with a 24-70mm lens with the following results:
@24mm: -3 to +7 => +2
@50mm: -3 to +4 => -1.5
@70mm: -5 to +8 => +1.5
If you average the three together, you're looking at a +.67 adjustment. So round up to +1 and that's the proper adjustment, or should the adjustment ideally be the same at any focal length of the zoom lens and the lens should be calibrated by the manufacturer?
You have a math error, but ultimately is doesn't change your number. Your adjustment at 50mm is wrong. -3 to +4 yields a +0.5, not a -1.5.
p.6 #15 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes
I gave this method a try with my Nikkor 85mm ƒ/1.8G. I already have it tuned so I thought it would be a good test. The resulting range where I got an unwavering digital rangefinder "dot" was nearly 75% of the range of adjustments: 11 to -19.
That hardly gives me a sense of confidence.
That said, the center of that range, -4, is only one off of what I had previously determined to be the correct adjustment of -5.
I had less luck applying this technique to my 70-200/4 zoom. The rangefinder inconsistency seemed greater at some focal lengths than others. In fact, at 200mm, the rangefinder thought every single adjustment, 20 to -20 was in focus… not helpful, especially since test photos showed otherwise.
p.6 #20 · Dot-Tune: Autofocus Fine Tuning in under 5 minutes
OK first let me say im liking the idea of this method and when i have a spare couple of hours in the day i will have to give it a shot.
but I also have an idea (with a question) that may add to this method using Canon's softwre (i have no idea about nikons software)
when your tetherered and using Canon's softwre you can bring up the live view picture on screen. and you can also adjust focus using the '<<< < > >>> ' . my question is how do the smaller step <> buttons have any relation to a step in the MA values.?
if they do then you should be able to :
1:set you MA value to '0'
2: use Phase detect AF to focus on your target
3: using the canon software click > or < until you have the best focus. and count how many presses gave you the best focus.
4: set your MA value to the same number as the number of clicks gave the best focus.
5: put the lens out of focus and have it refocus
6: back to the screen and see if you have the best focus
Just a suggestion. if the <> steps are not in relation to the MA adjustments then it obviously wont work
PS
I would try this myself (and indeed will sometime soon) but at the moment I dont have a USB cable long enough to get my camera in a decent position to my Desctop . and my netbook seems not to like the canon software / tethered camera
