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Author Topic: Lens Calibration / Micro adjustment  (Read 5743 times)

prossernoski

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Lens Calibration / Micro adjustment
« on: October 20, 2011, 10:08:19 AM »
is it all its cracked up to be?

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Lens Calibration / Micro adjustment
« on: October 20, 2011, 10:08:19 AM »

neuroanatomist

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Re: Lens Calibration / Micro adjustment
« Reply #1 on: October 20, 2011, 10:17:36 AM »
Yes.
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prossernoski

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Re: Lens Calibration / Micro adjustment
« Reply #2 on: October 20, 2011, 10:21:33 AM »
LOL!

have the following;...

70-200 2.8 ii
50mm f1.2
24-105 f4
20-35 ef OLD one
and a really old 50mm macro

Any tips in getting the best results?

Mate has the spyder thingy but it came with no instructions, looking on the net we did it all wrong so will give it another go but sometimes users are better to get information from rather than an obscure website...

thanks in advance...

neuroanatomist

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Re: Lens Calibration / Micro adjustment
« Reply #3 on: October 20, 2011, 10:22:08 AM »
But seriously, AFMA can make a huge difference in your percentage of in-focus shots, especially for wide-aperture lenses.  If you only use variable zooms (e.g. f/3.5-5.6) or 'slow' lenses (f/4 and narrower), you will likely not get much benefit from AFMA.
« Last Edit: October 20, 2011, 10:36:49 AM by neuroanatomist »
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prossernoski

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Re: Lens Calibration / Micro adjustment
« Reply #4 on: October 20, 2011, 10:25:30 AM »
have found my 24-105 slightly off - but that could be my naff technique eh! ;-) the 70-200 seems fine and the 50 might be a tad out

the old lenses are really old and just wanted to ensure they were ok on the camera rather than faffing around...

neuroanatomist

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Re: Lens Calibration / Micro adjustment
« Reply #5 on: October 20, 2011, 10:37:12 AM »
I'm actually writing up a detailed tip which will be posted on the TDP forums in the next few days.  The short version for now is get a tool (which you've done), then:

  • set up the tool on table or tripod, making sure it's level
  • best to light it with two lights, one on the focus target and one on the ruler, or outside on a sunny day
  • set up camera, I use a distance of ~25x the focal length
  • make sure camera is level and the center AF point is centered on the focus target
  • set camera in Av or M, aperture to max, jpg with monochrome picture style
  • shoot several shots at each AMFA setting - I do 8 total (2 starting at infinity, then 2 without refocusing, then 2 starting at the minimum focus distance, then 2 without refocusing
  • to save time, you can iteratively bracket (e.g. shoot at -10, 0, +10, then narrow it down further
  • review images at 100% on your computer
  • sometimes, 3-4 adjustment values will look ok, e.g. +1 to +3, so use the average
 

Hope that helps...
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prossernoski

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Re: Lens Calibration / Micro adjustment
« Reply #6 on: October 20, 2011, 10:40:31 AM »
EXCELLENT! many many thanks! ;D

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Re: Lens Calibration / Micro adjustment
« Reply #6 on: October 20, 2011, 10:40:31 AM »

JR

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Re: Lens Calibration / Micro adjustment
« Reply #7 on: October 20, 2011, 10:54:57 AM »
I got the SpyderLenscal myself and got so discouraged trying to micro adjust my 50mm 1.2L that I gave up.  What ever result I got using a short distance to the ruler (like 2 feet), then those result no longer hold good when I was shooting from 5-10 feet with the camera.  So at first I thought I needed -5 when at close range but then 0 worked best when further then 5-10 feet from the ruler. (using f1.4)

Reading your comments Neuro I am starting to wonder I might have done it all wrong!  First, when you say ~25x the focal lenght, do you mean say 25 x 50 mm = 125 cm or ~4ft? 

Also, when you say "shoot several shots at each AMFA setting - I do 8 total (2 starting at infinity, then 2 without refocusing, then 2 starting at the minimum focus distance, then 2 without refocusing)", so do you mean you do all your test using manual focus?  And when doing these 8 shots above, do you always stay at the same distance from the ruler?

Sorry if my question is stupid!  I just know I did it all wrong...as you can see I am trying everything I can to increase the % of in focus shots with my 50 1.2 (from microadjustment to the ST-E2 speedlite transmitter  ???)


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neuroanatomist

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Re: Lens Calibration / Micro adjustment
« Reply #8 on: October 24, 2011, 10:55:21 AM »
Reading your comments Neuro I am starting to wonder I might have done it all wrong!  First, when you say ~25x the focal lenght, do you mean say 25 x 50 mm = 125 cm or ~4ft? 

Also, when you say "shoot several shots at each AMFA setting - I do 8 total (2 starting at infinity, then 2 without refocusing, then 2 starting at the minimum focus distance, then 2 without refocusing)", so do you mean you do all your test using manual focus?  And when doing these 8 shots above, do you always stay at the same distance from the ruler?


Yes, 25x the focal length would be 25 x 50mm = 1250mm = ~4 feet.

All the shots are the same distance from the ruler, and you need to use AF for AFMA.  What I mean is that for the first shot, I turn the manual focus ring on the lens until it's set at infinity, then activate AF and take the shot.  Then I turn the MF ring to infinity again, AF, shoot.  Then just shoot twice without manually changing the focus before shooting.  Then I turn the MF ring to the minimum focus distance, AF and shoot, repeat, then two more shots without moving the MF ring.  Hope that clarifies.

I got the SpyderLenscal myself and got so discouraged trying to micro adjust my 50mm 1.2L that I gave up.  ...as you can see I am trying everything I can to increase the % of in focus shots with my 50 1.2 (from microadjustment to the ST-E2 speedlite transmitter


Two words:  focus shift.

The 50mm f/1.2L is something of a special case.  That lens suffers from a particularly bad focus shift (many lenses have some focus shift, especially, fast primes, but usually not enough to notice).  Focus shift is when the focal plane of the lens changes when you change the aperture of the lens.  All lenses focus with the aperture wide open, then stop down the aperture to your chosen setting as the shot is taken.  In the case of the 50mm f/1.2L, if you select an aperture narrower than f/1.2, down to about f/4, focus shift means that the lens will actually focus on a point that's behind your chosen focal plane.  At f/4 or a little narrower, the DoF is deep enough to mask the effect, because by then your chosen focal plane is within the DoF.  At very close subject distances, the DoF is shallower, and the effect of focus shift is exaggerated (you may need f/5.6 or even f/8 to get a deep enough DoF to mask the shift).

So, what can you do?  Here are some options:

  • Stop down to f/4 or narrower.  But, I'm going to assume that shooting at f/8 is not the ideal solution...
  • Shoot at f/1.2.  There's no shift if you don't stop down.
  • Use Live View.  Granted, that's not a good option with typical 50/1.2 subjects.
  • Manual focus with the DoF Preview button pressed.  You'd almost certainly need the Eg-S focusing screen instead of the stock screen.
  • More complex AFMA.  You could perform an AFMA at f/2, and you'd get different results than wide open - that adjustment would compensate for the focus shift at f/2, but not be applicable at f/1.6 or f/2.8, for example.  So, you'd need to have a list of AFMA values, and change the setting to match the aperture you want to shoot at.  Might work if you can pick an aperture for a shoot and stay there.  (Side note here: the 1D X can store two AFMA settings for a zoom lens, one for the wide end and one for the long end; in theory, Canon could allow multiple, aperture-dependent AFMA settings for the 50L, which would certainly help with this issue.)
  • Intentionally front focus.  Use an AF point over a feature that's a little bit in front of what you really want to focus on.
  • Tweak on the fly.  The 50L has full-time manual focus, so you can use AF get you close, then turn the MF ring slightly to bring the focal plane forward a little.  You'd likely want to be using back-button AF for that, and it would take a fair bit of practice to get it working reliably.

The 50L can deliver amazing shots, but due to the focus shift issue it takes some work and practice to get the most from the lens.

Good luck!
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JR

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Re: Lens Calibration / Micro adjustment
« Reply #9 on: October 24, 2011, 04:51:56 PM »
Thanks for taking the time to respond to my question Neuro.  This is a very good and detailed description of what is hapenning with my 50mm 1.2L.  For the first I think I understand the focus shift you describe and now understand why this lens is tricky sometimes...

I actually tried the AF back button this afternoon with with my 85mm 1.2L.  I will try it with the 50mm tonight and see what happens.  I also ordered the ST-E2 transmitter which should get here tomorrow so with that and the back AF button, I think I am on to something.  Funny that My 85 1.2 does not seem to have this focus shift or at least not as pronounce.  Either way, I would not change the 50 1.2 as when I put back my 50 1.4 on my cameras, I usually swap it back for the 1.2L version very quickly.

For now I will try more to increase my % of in focus shots with th etransmitter and your focusing suggestions above, and leave the micro adjustment aside ...

Thanks again...
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well_dunno

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Re: Lens Calibration / Micro adjustment
« Reply #10 on: January 23, 2012, 02:09:37 PM »
Neuro - thanks ever once again for sharing your knowledge! Very useful info!

I was also wondering about cam-lens calibration carried out by Canon. Does this pose any risks (not sure what the procedure is but if the lens(es) risk coming back with some other issue, it might not be worth)? Also, once calibrated, the lens should be sharp throughout the focal range, shouldn't it?

A last question,  is it always the lens being calibrated in relation to the cam, or both ways? In other words, if you have two cams one front-focusing and another back-focusing with the same lens, can the cam-lens calibrations get everything in line, or is it either one cam or the other...

Cheers!


neuroanatomist

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Re: Lens Calibration / Micro adjustment
« Reply #11 on: January 23, 2012, 02:23:09 PM »
I was also wondering about cam-lens calibration carried out by Canon. Does this pose any risks (not sure what the procedure is but if the lens(es) risk coming back with some other issue, it might not be worth)? Also, once calibrated, the lens should be sharp throughout the focal range, shouldn't it?

A last question,  is it always the lens being calibrated in relation to the cam, or both ways? In other words, if you have two cams one front-focusing and another back-focusing with the same lens, can the cam-lens calibrations get everything in line, or is it either one cam or the other...

As I understand it, when Canon 'calibrates' a camera and/or lens, they do their best to set the baseline to zero on everything, rather than specifically trying to match lens to body. 

As to the lens being sharp throughout the focal range, that depends on the lens.  Generally, zoom lenses are sharper in some parts of the focal range than others, due to the design of the lens itself - I don't expect that calibration would change that.
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well_dunno

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Re: Lens Calibration / Micro adjustment
« Reply #12 on: January 23, 2012, 02:40:08 PM »
Thank you!!

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Re: Lens Calibration / Micro adjustment
« Reply #12 on: January 23, 2012, 02:40:08 PM »

drmikeinpdx

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Re: Lens Calibration / Micro adjustment
« Reply #13 on: January 23, 2012, 05:45:08 PM »
A few months ago I sent my 17-55 2.8 IS lens in to Canon service because it front focused dramatically at the wide end of the zoom range.  When it came back, it back focused at the narrow end of the zoom range. 

I sent it in again and they had me send in my 7D as well.

When the camera and lens came back together, they now front focused at the wide end of the zoom range, much like they did in the beginning. 

I did some more extensive testing putting that lens on different bodies and using the 7D with different lenses from my collection.   The body had similar problems with other zoom lenses, but in different parts of the zoom range!  Oddly, prime lenses still worked perfectly.   

The 17-55 lens showed wild focus problems on my 40D body, I think still front focused at the wide end.  (Don't have my notes with me now.)

So I speculate that Canon service attempted to adjust the programming in the body to make it work with a defective lens.  I really don't know if that is correct.   I have not been able to find a full explanation of how the focus algorithms are supposed to work, when they are working correctly.

The whole focus system sucks if you ask me.

Right now the lens and the 7D are back at Canon service for a third attempt.  I sent them to New Jersey this time instead of California.

Mike
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marekjoz

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Re: Lens Calibration / Micro adjustment
« Reply #14 on: January 23, 2012, 07:38:44 PM »
A few months ago I sent my 17-55 2.8 IS lens in to Canon service because it front focused dramatically at the wide end of the zoom range.  When it came back, it back focused at the narrow end of the zoom range. 

I sent it in again and they had me send in my 7D as well.

When the camera and lens came back together, they now front focused at the wide end of the zoom range, much like they did in the beginning. 

I did some more extensive testing putting that lens on different bodies and using the 7D with different lenses from my collection.   The body had similar problems with other zoom lenses, but in different parts of the zoom range!  Oddly, prime lenses still worked perfectly.   

The 17-55 lens showed wild focus problems on my 40D body, I think still front focused at the wide end.  (Don't have my notes with me now.)

So I speculate that Canon service attempted to adjust the programming in the body to make it work with a defective lens.  I really don't know if that is correct.   I have not been able to find a full explanation of how the focus algorithms are supposed to work, when they are working correctly.

The whole focus system sucks if you ask me.

Right now the lens and the 7D are back at Canon service for a third attempt.  I sent them to New Jersey this time instead of California.

Mike


Mike,
have you read this: http://www.canonrumors.com/tech-articles/this-lens-is-soft-and-other-myths/ ?
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Re: Lens Calibration / Micro adjustment
« Reply #14 on: January 23, 2012, 07:38:44 PM »