AF Micro-Adjustment tool

[Bart_van_der_Wolf]

Bart,

I'll add my name to the thankyou list, sterling work.

Thanks John,

I've since set-up two modified 1DMkIII's with an array of lenses upto and including the EF600 with a 1.4TC, your chart does an excellent job.

How did you manage the 600, did you use the AF Microadjustment target (with 'relatively close' focusing) or by some other means?

I just wish they were my 1DMkIII's, they seem to be much better at low light AF than my 1DNs.

Who knows what the future has in store for you? Besides, maybe a Mark III successor does even better.

Bart

 

[John_Nevill]

How did you manage the 600, did you use the AF Microadjustment target (with 'relatively close' focusing) or by some other means?
Bart

Set the EF 600 (+/- 1.4tc) on a large Gitzo with black-widow gimbal (locked down) ~35ft away (all indoors) from the laptop, then used same method as above.

Then tested it on a paperback set outside at a distance of ~60ft. I found the EF600 was +5 and -12 with 1.4TC.

The guy who uses the EF600 is birder and normally uses the rig at these distances. The difference was quite noticeable. The paperback's soft text turned into crisp text.

Surprisingly, the moire was quite visible.

 

[Bart_van_der_Wolf]

The guy who uses the EF600 is birder and normally uses the rig at these distances. The difference was quite noticeable. The paperback's soft text turned into crisp text.

Surprisingly, the moire was quite visible.

Thanks, good to know the moiré showed clearly at 35 feet (=approx. 1:18 magnification factor) and the adjustment remained valid at larger distances, it might also help others to know that.

At that magnification factor, and assuming an average computer monitor LCD element pitch, the central part of the cross-hairs target is still fully resolved, and the off-centre part even better. This wil produce a high enough modulation to clash with the lower resolution camera LCD. Theory and practice still agree. It also proves that the lens has a high resolution at that shorter distance, because high resolution causes high amplitude moiré.

Thanks for the feedback,
Bart

 

[John_Nevill]

It also proves that the lens has a high resolution at that shorter distance, because high resolution causes high amplitude moiré.
Bart

That's exactly what I found, the moire had a different frequency from what was seen on the EF70-200, but visible nonetheless

 

[Steve Saunders]

Well done Bart and thanks, this will keep us busy for a while.

 

[John_Nevill]

Bart,

Just a quick update to let you know that I set up a Nikon D3 last weekend with a few Sigma lenses (100-300 f/2.8 and 70-200 f/2.8). Your micro adjust target worked extremely well. Ironically, all lenses were spot on (needing no adjustment) with and without the Sigma TCs, so the D3 owner was a happy chap!

 

[Bart_van_der_Wolf]

Just a quick update to let you know that I set up a Nikon D3 last weekend with a few Sigma lenses (100-300 f/2.8 and 70-200 f/2.8). Your micro adjust target worked extremely well.

John, thanks for the feedback. I'm glad the D3's sensor resolution also aliases with the camera LCD that Nikon uses.

Ironically, all lenses were spot on (needing no adjustment) with and without the Sigma TCs, so the D3 owner was a happy chap!

Well, it must be a comforting feeling having it confirmed anyway. Now the only remaining weak link that can be blamed, is the photographer ;-)

Bart

 

[Tom Darby]

Thank you

Thanks Bart! Just finished using this on my 24-105 and found that it is shooting perfectly without any adjustments. I was wondering if there was any patterns developing with adjustments being the same for specific lens but it seems they aren't from my reading here.

Appreciate your efforts here!

Tom

 

[Bart_van_der_Wolf]

Thanks Bart! Just finished using this on my 24-105 and found that it is shooting perfectly without any adjustments.

Hi Tom, that's good news. I'm always a bit suspicious when something turns out 'exactly' within specs (in fact with this test it's got to be exactly right), but then I'm versed enough in statistics to know that perfection does exist!

I was wondering if there was any patterns developing with adjustments being the same for specific lens but it seems they aren't from my reading here.

You've got the right attitude as far as I'm concerned, don't take things at face value, dare to be critical, it'll allow to achieve improvement. I'm curious as to any differences between 24 and 105mm though. Were they both spot on, or is there a difference you could detect? Again, not something that should happen, but it's only too plausible that it will.

Appreciate your efforts here!

And also thank you for the feedback. Without feedback, I would not have known if my efforts served anyone's purposes as well as they did mine. The direct, and indirect, feedback shows I've helped quite a number of people, which was the goal of making things public.

Bart

 

[Greg Edwards]

I would like to give a few chest compressions to this thread to see if I can get it back to life as I need help understanding this focus test/adjustment method.

I’m at that stage of photography where I know just enough to confuse the hell outta myself! I recently purchased a gently used 1DmkIII and I would like to take advantage of the micro AF adjustment feature this body has.

I’ve read this thread…a few times…and I think it is ingenious way to figure out if our lenses need an adjustment…but before I give this a go I have a few questions. Hopefully Bart or someone else with more experience doing this can help me out.

Please know I try to operate under the “no question is a stupid question”…even though I feel pretty stupid at the moment asking these questions…go figure!

1. Do I use the chart “as is” on my computer monitor (LCD) or do I have to save the .gif file and view it in any viewer (CS3/LR, etc) that will zoom in to 100%? In other words should the test image on my screen be blown up to 100% with the cross hairs at the center?
2. I’d assume turn IS off and remove UV filter. Yes, no, doesn’t matter?
3. Focus manually on the cross hairs of the test chart (at 5x or 10x) on my monitor until I see ________? This is where I’m a bit confused as “moiré” is a new term to me. I tried it briefly last night, with no tripod, and when using LiveView and focusing manually I could get the test chart to be sharp and “see” a cascading horizontal grayish lines (presumably the refresh rate?) repeating on the cameras LCD. Is this the moiré effect? I clearly don’t know anything about aliasing, moiré, low pass, pick-n-rolls and karate chops….please forgive…

I guess I really don’t know what to look for... These are the lenses I would like to calibrate to my 1D mark III:
Canon 70-200L 2.8 IS
Canon 85L 1.2
Canon 24-70L 2.8
Canon 16-35L 2.8

If I survive doing those…then I may also try my
Canon 100 2.8 macro
Canon 50 1.8
Sigma 15 2.8 fisheye

Thanks again Bart for this technique!

 

[Emil Martinec]

I thought I would report some comments on the test target I saw over at Naturescapes; see the post by Len Shepard in

http://www.naturescapes.net/phpBB3/viewtopic.php?f=1&t=133075

Sounds like he is suggesting the AF system could get confused due to the regularity of the pattern in the test target. Perhaps a suitable modification of the central region to break up the target's regularity could result in improvement in the testing regimen.

 

[Bart_van_der_Wolf]

I thought I would report some comments on the test target I saw over at Naturescapes; see the post by Len Shepard in

http://www.naturescapes.net/phpBB3/viewtopic.php?f=1&t=133075

Sounds like he is suggesting the AF system could get confused due to the regularity of the pattern in the test target. Perhaps a suitable modification of the central region to break up the target's regularity could result in improvement in the testing regimen.

Hi Emil,

Thanks for that link. However, I don't fully agree with Len's comment (anyway, not without some usable evidence instead of speculation). That's not because I would have a problem with a critique, no, I even encourage it (embracing the scientific principle of peer review)!

The central region of my target design (as simple as it looks, there's more to it than meets 'the eye'), where the central (cross) focus sensor point is supposed to do its work, is the most critical area. I specifically increased the density of 'easy' structures, and reduced the potentially confusing patterns (with a denser dither pattern) towards that center. The resulting in-focus aliasing is supposed to produce even higher amplitude/easier/coarser patterns from such a (flat plane) subject.

There is IMHO no way (and I'm seriously provoking proof to the contrary here) that a phase based focusing system could confuse the in-focus situation with an out-of-focus situation, since the moiré (as well as the bull's eye) amplitude is maximized at the perfect-focus setting. Let's not forget that we're talking about a deliberately flat plane, not a +/- 45 degree angled target with paper structure that could confuse the AF-system. Every in-focus response adds to the optimal solution, while all de-focus solutions rapidly detract from the phase modulation.

I did receive a couple of requests (also by email) in the last few days about clarifying/illustrating what the maximized moiré looks like. If I'm not beaten to it by others, I'll make a few captures of what it could look like (the actual appearance varies due to wide-open lens quality, and distance, and as such differs a bit between systems). I'll try to post the results over the weekend.

Bart

 

[Bart_van_der_Wolf]

I would like to give a few chest compressions to this thread to see if I can get it back to life as I need help understanding this focus test/adjustment method.

LOL, no resuscitation required if things are clear (life goes on), but questions for further clarification are of course welcome.

1. Do I use the chart “as is” on my computer monitor (LCD) or do I have to save the .gif file and view it in any viewer (CS3/LR, etc) that will zoom in to 100%? In other words should the test image on my screen be blown up to 100% with the cross hairs at the center?

Just make sure that the software you are using to view the target, displays without resampling, IOW at 100% zoom setting (actual size), and that your LCD monitor is set to its native resolution. Resampling would introduce its own aliasing, even without an additional regular sampling grid.

2. I’d assume turn IS off and remove UV filter. Yes, no, doesn’t matter?

Assuming you aim at the target from a tripod (otherwise you'll probably see camera movement aliasing patterns), it's best to disable IS (since not all versions switch off when tripod use is sensed). When attempting calibration with a handheld setup, IS will help to stabilize the movement artifacts.

Any front mounted filter will reduce the overall resolution, while insertion type of filters (on longer tele lenses) are an integral part of the optical optimization. Either way, when a filter is used, the resulting optical path will change and affect the optimal microadjustment. So if you more oftenly than not use a (front mounted) filter, I'd suggest to also use it for AF microadjustment, even though it might reduce the moiré amplitude a bit. In fact, the target allows to determine if there is a noticable effect with/without filter use, given a certain calibration.

3. Focus manually on the cross hairs of the test chart (at 5x or 10x) on my monitor until I see ________?

Moiré manifests itself as coarser patterns (aliases) than the underlying structures giving rise to the effect. Their shape/color/both depends on the optical distortions and focus differences that are introduced by the lens. When you see 'larger/coarser' structures appearing as you focus, you're witnessing aliasing effects.

This is where I’m a bit confused as “moiré” is a new term to me. I tried it briefly last night, with no tripod, and when using LiveView and focusing manually I could get the test chart to be sharp and “see” a cascading horizontal grayish lines (presumably the refresh rate?) repeating on the cameras LCD. Is this the moiré effect?

Yes, although they might be invoked by the camera movement itself. It's best to use a steady/tripod mounted camera setup, since that will also reduce minor front-to-back distance variations. The target will reveal all minor deviations, so it's best to eliminate as many variables as possible for calibration. I'll try to post some example of LCD viewable moiré patterns this weekend.

Camera shake during actual shooting will affect actual focus performance, also after calibration. I wouldn't be surprised if some of the published AF accuracy 'AI tests' are affected by camera shake (which may create temporal integration phase amplitudes that overpower actual focus accuracy phase differences).

Bart

 

[Ralph Honsbeek]

first attempt

Hi there ,

After one using the 1d Mark 3 for less than a month , I have found it quite hard to get the setup right. On my 40 D everything was perfect, just had to add a lens and shoot no problems. Now nothing but problems.

I have my 24-105 almost to my liking I think at -2 micro adjustment. But even now I am not
happy with it 100%

However I find calibrating my 200mm 2.8F L USM is a bit more challenging.
After using the Moire and a few distance setups 0 micro adjust seemed right to me and
I left it like that. I went out for a shoot and the problems are as followed.
When I subject cheek is aimed the eyes get in focus. The difference is very small but still
noticeable. If the AF point is selected and the images gets focus a little behind it , how should I go about adjusting the Micro Adjustments , plus or minus ?

Also , when calibrating the micro adjust as suggested in this forum my Mr. Van der Wolf ,
When using LiveView and MF to obtain perfect Moire , then going back to AF and looking ate the BARREL indicators, I wonder what it means if when barrel moves Left or Right,
If it moves to the right (More distance) will I have to add more - micro or more + micro > ?

Thank you for now

Ralph

 

[Bart_van_der_Wolf]

Moiré manifests itself as coarser patterns (aliases) than the underlying structures giving rise to the effect. Their shape/color/both depends on the optical distortions and focus differences that are introduced by the lens. When you see 'larger/coarser' structures appearing as you focus, you're witnessing aliasing effects.

Here are 2 examples of what moiré could look like:

The example on the left shows saturated color bands instead of a 50% gray background. The example on the right shows a mottled (and colored) background. Both types of pattern reach their maximum amplitude when focus is optimal. The size/frequency, and amplitude of the patterns depends on shooting distance and focal length. The higher the optical quality of the lens at its maximum aperture, the easier it will generate such patterns.

The shape and size of the aliases is hard to predict, so one should look for any background pattern that's not uniform gray. When it is hard to get a clear moiré effect, try shooting from another distance. When the camera's optical axis is perpendicular to the LCD screen, then the patterns will appear uniformly across the display. In the example above one can see a slightly higher amplitude towards the lower left, which indicates a slightly non-perpendicular shooting angle (despite the setup alignment with a mirror).

Bart

 

[Ralph Honsbeek]

One more question to ad to the confusion ...

Will adjusting the micro adjustment settings , 100% resolve any AF imbalance , or could
a persisting problem need Service Center assistance ?

I keep getting a false AF result. Focusing the AF point on let's say someone's nose and the nose is not in focus but the eyes a little deeper get crystal clear focus. Same with a flower, when I center the AF point on the petal the leaves get in focus or vice versa What is my problem here ?

Thank you

 

[Bart_van_der_Wolf]

When I subject cheek is aimed the eyes get in focus. The difference is very small but still noticeable. If the AF point is selected and the images gets focus a little behind it , how should I go about adjusting the Micro Adjustments , plus or minus ?

The AF Microadjustment should be set to perfect focus on a flat plane. If I understand you correctly, then you see a focus difference between the cheeks and the eyes. That is a fact of life when viewing at the pixel level. Depth of Field (DOF) is very limited at f/2.8 and 200mm focal length. For instance, when you shoot at 2 metres distance, you'll have 5 millimetres (approx. 1/5th of an inch) total DOF beyond which you will see a noticable degradation of sharpness at the pixel level. At 3 metres focus distance, you stil have only some 12 millimetres (less than half an inch) of total DOF at the pixel level beyond which you see reduced sharpness. That's how critical the 1Ds Mark III will let you focus, and that's why the AF Microadjustment is so valuable. How much of that is visible in the output, depends on output size and viewing distance.

Also , when calibrating the micro adjust as suggested in this forum my Mr. Van der Wolf ,
When using LiveView and MF to obtain perfect Moire , then going back to AF and looking ate the BARREL indicators, I wonder what it means if when barrel moves Left or Right,
If it moves to the right (More distance) will I have to add more - micro or more + micro > ?

While it sometimes seems hard to interpret, it is logical when you realise that the -/+ adjustment moves the actual AF focus plane forward/backward. So, when the AF focuses at a farther distance than it should, you need to adjust it it to a nearer distance, forewards. It could have helped if Canon had marked the scale nearer/farther (-/+).

Bart

 

[Bart_van_der_Wolf]

Will adjusting the micro adjustment settings , 100% resolve any AF imbalance , or could a persisting problem need Service Center assistance ?

Here's my view on it. On anything else than a flat plane perpendicular to the optical axis, it becomes hard to predict where the AF will decide what the best focus position is. With a few exceptions in specific lens designs (such as e.g. the EF-50mm f/1.2 L where distance plays a role), the focus algorithm will usually achieve reasonably consistent and repeatable results (small errors may also be introduced by hysteresis in the focus ring mechanism). Subject and or camera motion may also result in different phase maxima.

Potential sources of variation will be electronic noise which adds a variable to the focus motor feedback, some mechanical tolerance in the resting position of the focus mirror (the one behind the main mirror), and/or dust in the optical path towards the focus sensors. This will be the hardest type of tolerance to diagnose.

Another potential source of error on non-flat or variable contrast subjects could be caused by slight misalignment between the red squares projection, and the relative positions of the sensors across the actual field of view. The red squares are projected in the viewfinder, where as the focus sensors are near the bottom of the mirror box. To attempt and find the positioning accuracy, one could use a small detailed subject at close range placed in front of a distant background. By small horizonal and/or vertical displacements of the subject (it's best to keep the camera and background fixed), one could estimate how well centered the red squares are with respect to the presumed position of the actual focus sensors.

A consistent bias (on average) would indicate a cause that could be addressed by calibration and/or AF Microadjustment. A random deviation would point in the direction of a mechanical/electronic cause. When trying to single out a cause, it helps to be methodical.
Eliminate motion by focusing with a tripod mounted camera on a motionless scene (even using a remote control to focus can help). AF Microadjustment is simple enough to do well. One will still see some variation of AF, due to noise and mechanical tolerances. What remains are those random causes, they should however result in only small variations around the ideal focus position. Shooting subjects at an angle remains a bit of a gamble for any automatic system.

Bart

 

[Ralph Honsbeek]

I shot those with mu 24-105mm though

 

[Greg Edwards]

Here are 2 examples of what moiré could look like:

The example on the left shows saturated color bands instead of a 50% gray background. The example on the right shows a mottled (and colored) background. Both types of pattern reach their maximum amplitude when focus is optimal. The size/frequency, and amplitude of the patterns depends on shooting distance and focal length. The higher the optical quality of the lens at its maximum aperture, the easier it will generate such patterns.

The shape and size of the aliases is hard to predict, so one should look for any background pattern that's not uniform gray. When it is hard to get a clear moiré effect, try shooting from another distance. When the camera's optical axis is perpendicular to the LCD screen, then the patterns will appear uniformly across the display. In the example above one can see a slightly higher amplitude towards the lower left, which indicates a slightly non-perpendicular shooting angle (despite the setup alignment with a mirror).

Bart

Thank you Bart for taking the time to answer my questions...especially with visual aids! I will give this a try!

 

[Tim Dolan (Longwatcher)]

I want to thank you for producing the tool, it makes lens AF micro-adjustment quick and easy.

I had downloaded it when you first came out with it, but for some reason I can't remember I didn't get around to using it until yesterday.

I found that the lenses I use the most all needed adjustment and the ones I rarely use needed little if any.
I was most puzzled by my 85/1.2 needing more then I thought it would, while my 28-70/2.8L needed far less, but then my 85 has been missing focus more lately and I use it the most.

In a bit of humor, I was doing all of my lenses in turn and actually put my 24mm TS-E lens on to the camera before I realized that was kind of useless.

Otherwise I got all 9 lens and two extenders, although I just realized I only did the extenders with one lens and need to do them with the other.

 

[Bart_van_der_Wolf]

I want to thank you for producing the tool, it makes lens AF micro-adjustment quick and easy.

You're welcome. I originally put it together for my own use, but I realised that it would be of use to others as well. I do wonder how things look on the camera LCD of the latest Nikons with lifeview capability though. The pixel pitch is different, but presumably the effect is similar at different distances. Nikon owner feedback on AF accuracy would be appreciated.

I found that the lenses I use the most all needed adjustment and the ones I rarely use needed little if any.
I was most puzzled by my 85/1.2 needing more then I thought it would, while my 28-70/2.8L needed far less, but then my 85 has been missing focus more lately and I use it the most.

One cannot easily predict the amount of correction needed. The adjustments are very minute per unit, and they are in fractional DOF amounts. Since DOF varies (amongst others) with focal length and aperture, larger values by themself don't mean that much. It only means that for the specific mechanical body/lens combination (mechanical is by definition somewhat variable), a software adjustment is usually needed for best performance.

I've had my EF 24-70mm f/2.8 L serviced recently, and at 70mm it went from +4 to +16 microadjustment ! Anyway, it's very sharp (after adjustment). I love the possibility to self adjust.

Anyway, it's still important to test the resulting correction on real subjects, because there might still be some correction necessary with more ambiguous subjects than flat subjects. There can also be some mechanical play and hysteresis in the lens drive mechanism. Multiple shots of the same subject will give a feel for average deviations that might warrant an additional correction.

In a bit of humor, I was doing all of my lenses in turn and actually put my 24mm TS-E lens on to the camera before I realized that was kind of useless.

Well not entirely useless, as you can also use the TS-E lenses untilted ... I also get pretty good correllation on a single/central focus point, and on flat planes. My TS-E 90mm is very sharp/contrasty at wide apertures, so it can also be used as a regular (manual focus) lens. The 45mm version is also very sharp, but has a bit of Chromatic Aberration that needs some postprocessing.

Otherwise I got all 9 lens and two extenders, although I just realized I only did the extenders with one lens and need to do them with the other.

Yes, the focus accuracy with/without extenders can be quite different due to the added mechanical tolerances/variations. Again, AF microadjustment is very useful for getting that difference neutralized.

Bart

 

[Tim Dolan (Longwatcher)]

Well not entirely useless, as you can also use the TS-E lenses untilted ... I also get pretty good correllation on a single/central focus point, and on flat planes. My TS-E 90mm is very sharp/contrasty at wide apertures, so it can also be used as a regular (manual focus) lens. The 45mm version is also very sharp, but has a bit of Chromatic Aberration that needs some postprocessing.

Bart

I don't think you got the humor... The 24mm TSE lens is not useless, it is quite handy as a matter of fact, I use it for the occasional product shot and extreme angle model shots, but it is manual focus only, so setting a Auto-Focus micro-adjustment for that lens is kind of useless.

 

[Bart_van_der_Wolf]

I don't think you got the humor...

Oh, I did get the gist about that, but I didn't add an emoticon to show that.

The 24mm TSE lens is not useless, it is quite handy as a matter of fact, I use it for the occasional product shot and extreme angle model shots, but it is manual focus only, so setting a Auto-Focus micro-adjustment for that lens is kind of useless.

I do agree about the usefulness of T/S lenses, I have two of them myself. Yes, there is a contradiction in Auto-Focus micro-adjustment for a manual focus lens, but as it happens, the focus confirmation on manual lenses is also affected (

) by the micro-adjustment !! That's the more serious message I tried to get across.

On top of that, TS-E lenses are reported to give unreliable focus confirmation due to their tilt capability, but that isn't necessarily true for flat planes, in my experience.

Bart

 

[nicolas claris]

Just for info of you all, I just did today a comparison test between the Canon EF 14mm f/2.8L II USM and Sigma 12-24mm f/4.5-5.6 EX Aspherical DG HSM Autofocus Lens

To be sure to have both lenses in their best situation, I did a particuarly accurate microadjustment, following Bart's brilliant invention.
And then, just by curiosity, I made the shot with the Canon 14mm… phewwww!
100% Crop, ISO 100 - ƒ 2.8 no PP except save as JPEG in CS3 (be sure to see it at 100% on your screen):
http://mnclaris.free.fr/forum/14/_45R0589_C1_crop.jpg

The test can be seen here:
http://mnclaris.free.fr/forum/14/index.html
But please if you want to react, post here:
http://www.openphotographyforums.com/forums/showthread.php?p=54434#post54434

 

[Bart_van_der_Wolf]

And then, just by curiosity, I made the shot with the Canon 14mm… phewwww!

Yeah, that's some cruel challenge for the Raw converter! The lens is fine.

Just a small addition, not for Nicolas but as a general remark. Taking the shot is not necessary for the AF Microadjustment procedure that I presented in this thread. Optimal focus can be determined without firing a single shot, just by looking at the rear LCD in 'LifeView' and maximizing the amplitude of the aliasing patterns by optimizing (auto) focus.

Having said that, Nicolas' crop does show another manifestation of aliasing, 'enhanced' by the Raw processor used (the rear camera LCD shows a different aliasing). The crop also demonstrates that (as intended) the actual focusplane is aligned with the LCD screen.

Bart

 

[Ralph Honsbeek]

I am so sorry but this is not working out for at the moment.
The field of focus is so narrow for example the 200mm f2.8 that each time
I look for the Moire , each time seems a bit diffrent and indications on barrel
are not consistent.
My lens (200mm F2.8 L USM) was serviced and focus is now better but the guy there still didn't get it a 100% to my liking. It still seems to be front focusing.
Can you please advise on other methods on dealing with front focusing and to get it spot on.

Could I make for example 10 folders with each a different micro adjustment setting and
try it that way. Shot 10 different sequence shoots with diffrent micro settings then check the result on the computer LCD ?

Thank you

 

[Bart_van_der_Wolf]

I am so sorry but this is not working out for at the moment.
The field of focus is so narrow for example the 200mm f2.8 that each time
I look for the Moire , each time seems a bit diffrent and indications on barrel
are not consistent.

Hi Ralph,

Let's try to get this one solved, by using a workflow that should allow to get your AF Microadjustment close to perfect on average (there will still be some variation, but no bias). I also have a 200mm f/2.8, so I understand the difficulties with the narrow DOF range and one cannot utilize 'post-it' notes due to the distance scale being under a non-rotating window. By the way, this also demonstrates that maximum sharpness only exists in a very narrow range, narrower than the final DOF we may tolerate.

My lens (200mm F2.8 L USM) was serviced and focus is now better but the guy there still didn't get it a 100% to my liking. It still seems to be front focusing.

Well, if it's systematically front focusing, then at least the direction of adjustment (+ Backward) is obvious.

Can you please advise on other methods on dealing with front focusing and to get it spot on.

Here's a suggestion.

1. Find a distance at which you can achieve obvious moiré effects.
2. Use AF to achieve focus.
3. Using Life View, and assuming sub-optimal focus (otherwise quit ;-) ), note in which direction you need to manually adjust focus to maximize moiré.
4. Depending on the amount of adjustment needed, choose an adjustment amount and adjust in the direction to compensate for the direction of adjustment needed as determined in step 3.
5. go back to step 2. and do another iteration.

The amount of adjustment for each iteration depends on the total amount of adjustment needed. The theoretically fastest way to hone in on the optimal setting, is a binary one. Given you've already determined in which direction you need to adjust (in step 3.), over-adjust the maximum amount possible from your starting position. Then for each next iteration use half the amount to adjust in the opposite direction of the previous iteration.

Assuming one starts from a 0 adjustment setting, and a front focusing lens (requiring a positive adjustment direction to move the focus plane to the back), one could use +20 for the first iteration. This will probably over-correct to an AF backfocus situation. Then use an amount of -10 from the +20 starting point, so you'll use +10 for the next iteration. It then depends on which direction you need to correct manually, whether to use +/-5 (5 or 15) for the next iteration, use +/- 2 or 3 for the next, and +/- 1 for the final. When you over-correct then switch direction, otherwise use the same direction, but with half the amount of difference of the previous iteration.

The more difficult task is one of concentration, to choose the correct direction for the next iteration. Just remember, if you consistently need to manually correct towards a farther focus plane then use a more positive adjustment value, and obviously a more negative value if you need to manually focus nearer by than AF achieves.

Also don't forget to verify the settings you've found at different distances and when starting from either minimum or maximum focus starting position.

Bart

 

[Ralph Honsbeek]

Hi Bart,

I see what you are trying to say , but I must say your English is very technical , dare I ask what your profession is ? ^^
Let me give it a try and I'll be back if more things need explaining, thanks for the kind feedback

 

[Cem_Usakligil]

Hi Bart,

I see what you are trying to say , but I must say your English is very technical , dare I ask what your profession is ? ^^
Let me give it a try and I'll be back if more things need explaining, thanks for the kind feedback

I dare say that it is not the language but the subject topic which is very technical. I agree that many things can be explained in layman's language, but it takes more than twice the effort to compose such texts. And who has got the time to do it? ;-)

Cheers,