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Author Topic: Microadjustment  (Read 14938 times)

aldvan

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Re: Microadjustment
« Reply #15 on: August 31, 2011, 02:32:13 PM »
Please forgive me for starting a discussion that is becoming quite harsh...
By the way, although the idea to microadjust by a simple tool intrigued me at first, I'm convincing my self that the procedure suggested by Canon itself should be closer to the needs of the real world.
Rather, there are some points that I overlooked and that are very important.
The first one, as others already pointed in their post, is the perfect parallelism between camera and target (and this could be a point in favor of Lensalign).
The second one, that I forgot to do until now, is TO TURN OFF the image stabilizer...
I'll repeat the procedure next week end...

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Re: Microadjustment
« Reply #15 on: August 31, 2011, 02:32:13 PM »

Viggo

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Re: Microadjustment
« Reply #16 on: August 31, 2011, 02:57:27 PM »
You should also consider this one. I tried it and it made sense of the adjustments I already had done. (tried one we had in our camera-store were I work). It's ridicolously expensive so might want to pitch in with a few buddies ;oD

http://spyder.datacolor.com/product-cb-spyderlenscal.php
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neuroanatomist

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Re: Microadjustment
« Reply #17 on: August 31, 2011, 03:17:10 PM »
So whatever works for you, fine! But do not tell me that my method doesn't work, and for me it works much better, because aiming in between very long and very short distance to subject I get sharp POF on ALL distances. I did so with these lenses: ef 14L II, 24 1,4LII, 50L, 85L (twice) 70-200 II, 300 f2,8 L IS. That's the way it was and always will be.

Agreed.  I've gotten excellent results with the LensAlign Pro and a much longer list of lenses than yours, and it works for me.  If your method works for you, keep doing it!

I won't quibble, but I will correct a few inaccuracies:

Adjusting at mfd will never be accurate enough. At Northernlight they suggest you use at LEAST 50 times the focal to adjust.

Once again, not MFD.  The usual recommendation is 25-50x the focal length of the lens - frequently qualified by the advice to test at the most relevant/common subject distance for your typical subject(s).  Granted, that's not always easy because most people shoot more than one type of subject with a given lens. 

I have fiddled around with charts and moiré patterins at 1m or 2m

The problem there is not the distance, it's the other part of the statement - fiddling around with charts and moiré patterns.  Printed charts don't cut it, and moiré patterns have too much play (little to no discernable difference with a pretty large degree of axial movement) and problems with alignment.  You need to use the right tool for the job.  If your auto mechanic 'fiddled around' with a crescent wrench when working on your car's powertrain, instead of properly tightening the bolts with a torque wrench, you'd have maintenance issues down the line.

Your subsequent statement about the SpyderLensCal, "I tried it and it made sense of the adjustments I already had done," is totally consistent with what I'm saying here - when you use the right tool, you get accurate results.

First off, When you use 1dmkIV the focusing point is so large that it covers at least too much of those fine lines on a chart to be even remotley accurate.

With this and other, similar tools, you're not focusing on the ruler with the DoF scale - the ruler is at an angle to the vertical so the scale has depth, and your focus target is a larger square with a contrast scheme optimized to activate any AF sensor point geometry (horizontal- or vertical-line, cross-type, or diagonal cross-type) that is aligned to be parallel to the image plane (and thus orthogonal to the AF sensor).



The SpyderLensCal you linked to is constructed in the same way (but it seems to lack a feature to facilitate parallel alignment of the camera with the focusing target.



Rather, there are some points that I overlooked and that are very important....I'll repeat the procedure next week end...

One point that has not come up, but which is quite important, is what autofocus microadjustment really does.  What AFMA does is correct for systematic error in the AF system, specific to manufacturing tolerances in cameras and lenses.  It corrects for bias in the AF system, or put another way, it improves the accuracy of the AF system.  The terms accuracy and precision are sometimes (improperly) used interchangeably - accuracy is 'closeness to true' whereas precision is repeatability.  Here's a diagrammatic example:



AFMA corrects for accuracy but does nothing for precision.  Chuck Westfall has told me that, "The AF precision for the standard precision sensors is within the depth of focus for the maximum aperture of the lens, while the AF precision for the high precision sensors is within 1/2 or 1/3 the depth of focus for the maximum aperture of the lens, depending on the camera model under discussion."   Note that depth of focus is measured at the image plane of the sensor, and is different from (but affected by the same parameters as) the depth of field.  I interpret that to mean that although the precision is specified, for example with the f/2.8 sensor all the shots will be focused within a region that is 1/3 of the depth of focus deep for that lens' maximum aperture, focusing could still be inaccurate (i.e. it would look like case C above).

AFMA moves the center point - the 'average' focal plane of multiple measurements.  But it's important to remember that precision plays a role, so if you test your AF system with just one or a couple of tries, random chance says your test won't be 'spot on' due to imprecision.  So, when testing AF performance, you need to perform multiple tests for a given lens, and fewer tests would be needed for an f/2.8 or faster lens due to the higher precision.  I suspect this is what's behind Canon's statement that AFMA can prevent correct focusing - if you base an adjustment on one or two test shots, and those shots were relatively far off the correct focal plane, then on average most of your subsequent shots will miss focus.   

Bottom line - no camera will produce a perfectly focused image every time at every distance, period.  No adjustment procedure will change that.  What a proper AFMA can do is increase the percentage shots that are correctly focused. 
« Last Edit: August 31, 2011, 03:19:57 PM by neuroanatomist »
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neuroanatomist

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Re: Microadjustment
« Reply #18 on: August 31, 2011, 03:36:10 PM »
As a side note, some time back epsiloneri posted a very nice method for quantitatively determining the best AFMA setting.  It's something I plan to try when I get a chunk of free time.
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Viggo

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Re: Microadjustment
« Reply #19 on: August 31, 2011, 05:32:45 PM »
Well, fair enough, it seems that we actually agree on most things, and the rest I'm not going to discuss further.

The image you posted of the chart didn't include the whole thing (similiar to the spydercal) which was misleading at best. It look liked a printed chart. These tools seem to be the best solution. But I have found that when going shooting real life subjects, I still need to make adjustments, which kind of is crazy considering how much these tools cost.

The Spydercal has a level on it so it's simple to keep that and the camera parallell.
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neuroanatomist

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Re: Microadjustment
« Reply #20 on: August 31, 2011, 06:29:46 PM »
The image you posted of the chart didn't include the whole thing (similiar to the spydercal) which was misleading at best. It look liked a printed chart. These tools seem to be the best solution. But I have found that when going shooting real life subjects, I still need to make adjustments, which kind of is crazy considering how much these tools cost.

The Spydercal has a level on it so it's simple to keep that and the camera parallell.

Sorry about the misleading pic - I was looking for an image that showed the thin DoF you can easily measure with a tool like that.

I think that while they're expensive for what they are (production costs can't be very high), they're cheaper than almost any Canon lens and a LOT cheaper than even the cheapest L lens.  Like a good RAW converter, they're something that can benefit nearly every shot you take with your camera(s) and most lenses.   Worth it, IMO, especially considering the less than adequate results you can get with the free equivalents to those tools (I, too, have spent time with a cut-and-fold paper DoF chart!).

I didn't notice the SpyderCal has a level - that would do the trick, as do the sight gates on the LensAlign.  Both the SpyderCal and the new LensAlign MkII also fold flat, unlike my Pro version that takes up more space when stored.
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aldvan

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Re: Microadjustment
« Reply #21 on: September 03, 2011, 02:25:35 PM »
After reading and reading again all your posts, I spent a couple of days to setup a good microadjusting session. I opted for Jeffrey Friedl's method, that was well explained and didn't require to wait (and pay...) for a lensAlign to be shipped. The chart is well designed and the logic of the light grey indicators seems quite reasonable.
The lack of an instrumental system for a perfect alignment camera target required some additional time to spend leveling and measuring, but at last everything was perfectly aligned.
I started with the 1Ds3 and the 100-400, followed by the 5D2 and the same lens. At the beginning everything seemed working well, following well every step of the procedure. Frequently tested if the sensor was reading just the right target, turned off IS, fast shooting time, manually scanned from minimum distance to infinity before AF, camera on heavy tripod. Both cameras-lens seemed affected by a slight front-focusing corrected at -5 and -6.
Then, just for checking, I tried to set at -9 with the unlikely result to get again a front-focusing. Tried and tried again, getting similar results.
After reading an old article by Tom Jackson about the disalignment between the real sensor and the focus outlines in the viewfinder, I convinced my self that a lab procedure for microadjustment is risky and too exposed to minimal error factors.
So I reset everything and tomorrow I will go for what seems to me a more empirical and real world approach.
I will puth cameras and lenses on my tripod, aiming at the right distance for a wall plenty of contrasting and fine details. Then I will take 41 pictures focusing only with the central spot, adjusting from -20 to +20 and I will compare the results in LR3.4.
Quite rude but nor too time consuming, and it seems to me the exact procedure for what the MA system was  designed...
Any opinion?

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Re: Microadjustment
« Reply #21 on: September 03, 2011, 02:25:35 PM »

neuroanatomist

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Re: Microadjustment
« Reply #22 on: September 03, 2011, 10:25:32 PM »
Sorry, but to me it sounds like you tried the free method, and got what you paid for.  Even the blog post you mention recommends LensAlign - there's a reason for that. For one thing, that one horizontal line is not optimal for some sensor point geometries (bear in mind the guy who developed that chart shoots Nikon, and they don't use the high-precision diagonal center AF point found in some higher-end Canon bodies). 

Also, you plan to shoot just one shot for each adjustment, and possibly that's what you did the first time.  That's not a good plan - AF is accurate within a range, so you need several shots at each setting. Personally, I do 8 - two from infinity, then two without refocusing, then two from MFD, then two more without refocusing.  Given the requirement of many shots per setting, comparing sharpness in that 'wall test' will be quite a challenge.
« Last Edit: September 03, 2011, 11:48:15 PM by neuroanatomist »
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aldvan

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Re: Microadjustment
« Reply #23 on: September 04, 2011, 04:56:56 AM »
Neuroanatomist, I understand what you mean, but, at the same time, I'm beginning to understand also what Canon  states in 1Ds owner manual: "Do this adjustment only if necessary. Note that doing this adjustment may prevent correct focusing from being achieved".
You told about taking 8 shots for each adjustment. That speaks to me about a random behavior statistically corrected, badly exposed to the risk of any random process... I don't know, now...
Since I haven't focusing problems, I'm seriously tempted to let everything as mother Canon did... :-)

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Re: Microadjustment
« Reply #24 on: September 04, 2011, 06:10:02 AM »
I have microadjusted every lens, and although, before I found out how, it caused me many sleepless nights. BUT to see every picture not as sharp as it was with liveview-af or MF, is even worse. It takes some trial and error and if a lens is too off (like mye 300 f2,8 was) you need to get it hardware calibrated with Canon first, otherwise it won't help if you're at +20 or -20 with Ma.

What Canon do is solder one wire from one place to another in 4 steps. This is to move the POF a larger amount, and usually it helps a GREAT deal, but sometimes you find that your lens on your body is sharper in between those  steps, and needing the MA to make it juuuust right. If you own a 2,8 lens or slower, it's less noticeable, but for me, who mostly use 1,2 and 1,4 lenses, this is the difference between no shot or the perfect shot.

Neuroanatomist: I agree with you on that note, compared to not getting what you paid for in a lens, that can easily be corrected, they are cheap. But considering it when you hold the cheap piece of plastic in your hand and think that you paid half a 17-40 for it is kinda strange. Luckily for me I can borrow one from work. And as soon as I get back, I'll take your advice and properly set it up, and adjust all my lenses one more, well, not the TS 17mm  ;D

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neuroanatomist

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Re: Microadjustment
« Reply #25 on: September 04, 2011, 06:40:52 PM »
You told about taking 8 shots for each adjustment. That speaks to me about a random behavior statistically corrected, badly exposed to the risk of any random process... I don't know, now...
Since I haven't focusing problems, I'm seriously tempted to let everything as mother Canon did... :-)

That is exactly the way it works - any mechaincal (or biological, or physical) process has some degree of randomness.  AF is no different.  Not every shot will be perfectly focused, period.  Precision tells you how close one shot is likely to be to the next - with a high-precision center AF point and f/2.8 or faster lenses, shots fall in a range of 1/3 of the depth of focus at max aperture, with slower lenses, the precision is within one depth of focus at max aperture.  Accuracy is different than precision.  AFMA corrects for accuracy, but during the process of calibration, you still need to account for precision - thus, the multiple shots.  Less-than-ideal accuracy is most evident with a thin DoF (fast lenses shot wide open with fairly close subjects). 

You may not know you have a problem unless you prolerly test for it...

Neuroanatomist, I understand what you mean, but, at the same time, I'm beginning to understand also what Canon  states in 1Ds owner manual: "Do this adjustment only if necessary. Note that doing this adjustment may prevent correct focusing from being achieved".

Canon's advice is sound - I bet there are a lot of people out there who do the AFMA incorrectly, and end up in a worse place than no adjustment at all.  Done properly, it's wonderful - pros used to send bodies + lenses to Canon for this sort of calibration (that was behind the genesis of Canon Professional Services, actually).  Now, I can do it at home, my self, for less money and with faster turnaround.  Almost all of my lenses have some amount of AFMA, and I can't imagine shooting with lenses like the 85mm f/1.2L II or 135mm f/2L without that feature.
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aldvan

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Re: Microadjustment
« Reply #26 on: September 05, 2011, 01:33:34 AM »
Thank you, neuroanatomist. I'll bite the bullet and I'll order the LensAlign, although it is a steal! :-)

aldvan

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Re: Microadjustment
« Reply #27 on: September 05, 2011, 02:30:42 AM »
Just one more question. To get rid of the pain of taking out the card and downloading the pictures, could it be a good idea to connect the camera by EOS utilities to a computer and check the focus directly on the monitor?

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Re: Microadjustment
« Reply #27 on: September 05, 2011, 02:30:42 AM »

neuroanatomist

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Re: Microadjustment
« Reply #28 on: September 05, 2011, 07:24:22 AM »
Might work. I do find myself going back and forth to compare images, though.  I'd suggest using tethered shooting to narrow the range, but still shooting (capturing) multiple shots 3-4 units on either side of what initially seems to be the correct setting.
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Re: Microadjustment
« Reply #29 on: September 28, 2011, 04:20:33 AM »
After reading this thread I ordered a LensAlign MkII which finally turned up today. They posted quickly but mail from the USA to Australia seems to have been a bit slow lately. Anyway I thought I'd post my results after using it on my lenses with a 7D:

24-70mm f/2.8L, +5
50mm f/1.4, -1
70-200mm f/2.8L IS II, +2
100mm f/2.8L IS Macro, +8

So my two most used lenses the 50 and 70-200 were pretty much on the money, I've always been happy with them but it'll be interesting to see if they are just that little bit now, that may have been a small "problem I didn't know I had". The 24-70 I've mainly used for things where I didn't want too shallow DOF so it doesn't really suprise me I'd never noticed that one.

The 100mm macro was my last purchase and I hadn't been happy with autofocus, but being my first macro lens just put it down to the usual recommendations of tripod + manual focus for macro. After trying a few things like AI servo in case it was me moving too much I'd pretty much given up on handheld for anything approaching macro. After the adjustment I just wandered around the house doing a few hand-held test shots and now everything is bang on target.

Anyway that's a lens I see I'll get much more use from now, so I'm glad to have heard about the LensAlign and about focus adjustment in general which I must admit I didn't know about until I read this thread :).

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Re: Microadjustment
« Reply #29 on: September 28, 2011, 04:20:33 AM »