# Lens calibration or efforts making imperfect world perfect :)



## Efka76 (Feb 4, 2014)

Dear colleagues,

shortly I will describe my experience in lens calibration. I hope that this story will be useful to someone who wants to calibrate lenses but never done that before.

1-2 years ago I bought Canon 7d and number of lenses. My shots seems quite Ok for me. I did not notice any back / front focus issues. But that was due to the fact that I did not have a knowledge how to notice such things. But after spending some time in Canon rumours and reading various things about lens calibration I finally decided to try that.

My setup was following:

1) For lens calibration i bought Reikan Focal plus. Of course, Pro version is better but I thought that Plus version is sufficient as it allows fully automatic and semi-automatic calibation as well calibration target validation. Pro version is almost twice expensive as Plus version.

2) Photo studio - if you have option to do testing in bigger space, do that. My studio was almos 6 m long and of course it would be better to have bigger in order to test 200 mm lenses at x50 focal length. I selected studio for testing as it is controllable environment (light, no wind, it is easy to put calibration target on a wall.

3) Cheap tripod - it was not very convenient but for testing purposes this tripod was quite ok. During testing I target was not lost due to movements in tripod head. If you have good and expensive tripod it will be easier.

4) Calibration target - printed on laser jet on standard (lightweight) paper (Focal manual recommends using Matte Heavyweight paper, print should be performed on Inkjet). My target worked really ok in testing but if you have ability do everything as manual says 

5) Camera settings: AV mode, eye piece covered, etc. as indicated in manual.

6) Light level in all cased was higher than EV 8 (during my testing it was EV 8.2 - 8.9). For lighting I used halogen lights, background was lit by natural light from window and fluorescence lights. Of course such mix of lights was not very good but I tried to achieve higher EV. Light in terms of Kelvin was 5200. 

The testing:

1) Target validation - it was quite easy with all lenses; I just followed visual instructions and fixed tripod head when there was ok sign on computer screen. You just have to make sure that tripod / head / target are not moved during testing.

2) Canon 70-200 mm 2.8L II IS USM: very good test results achieved. Based on Neuro advice I tested zoom lenses at various focal lenghts (FL). The following FL were used: 70 mm., 100 mm, 140 mm and 200 mm. Focal Plus calculated the following AFMA adjustments for the above FL: +1 ; +3 ; +1 ; -1. Testing results show really very good quality of lenses. Due to the fact that only one AFMA value can be entered into Canon 7D i left AFMA as -1 but currently thinking to change it to 0 (mid value between min and max FL).

3) Tamron SP 24-70 2.8 VC. I really like these lenses, they are my walkaround lenses and I thought that they are quite sharp. Test results were the following: 24 mm (AFMA +1), 35 mm (AFMA +9), 50 mm (AFMA +13), 70 mm (AFMA +6). In camera AFMA +6 was written. Despite the fact that difference between both FL is only 5 I was unpleasantly surprised that in between of min and max FL sharpness is reduced quite dramatically  However, I now know what defficiency such lenses have and AFMA +6 at least will help me to have sharper images comparing to previous shots before calibration.

4) Canon 100 mm 2.8L IS Macro - I did 2 testings: @ x25 FL AFMA +7 and @x50 FL (recomended by manual) AFMA + 4. I entered +4 into camera. I was a bit surprised that i got 2 different AFMA values at different distances.

5) Canon EF-S 18-135. Due to the fact that thes lenses ar kit lenses I did not expect great results  Results are following: 18 mm (AFMA +13) and 135 mm (AFMA +6). In camera I entered AFMA +9. In testing it was very obvious that after AFMA adjustment images were much sharper. 

6) Canon 50 mm 1.4: I was really struggling with these lenses testing. At x25 FL distance I got AFMA +3, however, when I wanted to do testing @ x50 FL Reikan Focal Plus had issues: it performed many shots, however, was not able to collect reliable data for exact AFMA determination (indicator was red). I then tried test few more times at different distances from target. In few cases software was not able to collect reliable data, in one case I've got AFMA +4 (indicator was yellow, not green). I am wandering how to interpret such testing results. Does that indicate issues with my lenses or due to the fact that lenses are 1.4 it is much harder to obtain reliable results (light conditions were very good in all cases, EV 8.9). From testing I saw that AFMA values were in range of 3-5, accordingly I left AFMA +3 in camera.

Anyway, I have intentions to sell Canon 50 mm 1.4 and buy a new Sigma 1.4 Art series, when it is released. I really hope that Sigma will be much better than old design Canon lenses.

I hope that this my story will be helpful to some future testers  Also, I would appreciate if someone knowledgeable could comment on Canon 50 mm 1.4 testing results interpretation.


----------



## neuroanatomist (Feb 4, 2014)

Thanks for sharing!

Some comments...



Efka76 said:


> 6) Light level in all cased was higher than EV 8 (during my testing it was EV 8.2 - 8.9). For lighting I used halogen lights, background was lit by natural light from window and fluorescence lights. Of course such mix of lights was not very good but I tried to achieve higher EV. Light in terms of Kelvin was 5200.



That would be a bit low for my preference. IIRC, FoCal used to recommend EV >10 but dropped it to EV 8 some time back. I try to keep higher than EV 10, my values are usually in the 11-12 range. With longer/slower lenses especially, shutter speeds get a bit slow around EV 8, which can lead to vibration issues (even on a very stable tripod, if that tripod is on a hardwood floor, for example, you'll get vibration).




Efka76 said:


> 3) Tamron SP 24-70 2.8 VC. I really like these lenses, they are my walkaround lenses and I thought that they are quite sharp. Test results were the following: 24 mm (AFMA +1), 35 mm (AFMA +9), 50 mm (AFMA +13), 70 mm (AFMA +6). In camera AFMA +6 was written. *Despite the fact that difference between both FL is only 5 I was unpleasantly surprised that in between of min and max FL sharpness is reduced quite dramatically * However, I now know what defficiency such lenses have and AFMA +6 at least will help me to have sharper images comparing to previous shots before calibration.



The 'units' of the AFMA values are 1/8 the depth of focus for a given lens at max aperture. So, a difference of 5 units means more than 1/2 of the depth of focus for the lens. 




Efka76 said:


> 4) Canon 100 mm 2.8L IS Macro - I did 2 testings: @ x25 FL AFMA +7 and @x50 FL (recomended by manual) AFMA + 4. I entered +4 into camera. I was a bit surprised that i got 2 different AFMA values at different distances.



AFMA definitely changes with distance, but with longer lenses it's usually pretty stable beyond 25-30x FL. Totally anecdotal, but on my 5DII and 7D, I would sometimes see differences from 25x vs. 50x FL of 5-6 units, usually with wider lenses (16-35, 17-55, 35L, etc.). But on my 1D X, the largest difference between 25x vs. 50x that I see is 2 units, even with those same lenses (well, not the 17-55!). FWIW, my 100L was 2 units apart on all three bodies, and I also tested it at near-macro distance using the small target, the value was in the range of the 25-50x tests. 




Efka76 said:


> 6) Canon 50 mm 1.4: I was really struggling with these lenses testing. At x25 FL distance I got AFMA +3, however, when I wanted to do testing @ x50 FL Reikan Focal Plus had issues: it performed many shots, however, was not able to collect reliable data for exact AFMA determination (indicator was red). I then tried test few more times at different distances from target. In few cases software was not able to collect reliable data, in one case I've got AFMA +4 (indicator was yellow, not green). I am wandering how to interpret such testing results. Does that indicate issues with my lenses or due to the fact that lenses are 1.4 it is much harder to obtain reliable results (light conditions were very good in all cases, EV 8.9). From testing I saw that AFMA values were in range of 3-5, accordingly I left AFMA +3 in camera.



I've seen lots of reports of people having difficulty calibrating 50/1.4 and 50/1.2 lenses. DoF is so thin in those cases that setup stability and a fast shutter speed are critical, as well as minimizing any other sources of vibration (I did have some issues on a hardwood floor, none after moving the setup to the concrete slab in the basement). As above, EV 8.9 isn't really 'good light' - try getting it up to 11-12, and you might also try extending the mirror lockup delay in the FoCal settings (I think the default is 1 s). FWIW, I get 'good' or 'excellent' results with my 35/1.4 and 85/1.2 lenses.


----------



## dstppy (Feb 4, 2014)

Efka76 said:


> 3) Tamron SP 24-70 2.8 VC. I really like these lenses, they are my walkaround lenses and I thought that they are quite sharp. Test results were the following: 24 mm (AFMA +1), 35 mm (AFMA +9), 50 mm (AFMA +13), 70 mm (AFMA +6). In camera AFMA +6 was written. Despite the fact that difference between both FL is only 5 I was unpleasantly surprised that in between of min and max FL sharpness is reduced quite dramatically  However, I now know what defficiency such lenses have and AFMA +6 at least will help me to have sharper images comparing to previous shots before calibration.



I wanted this lens so badly . . . when I got it, the weight surprised me (why? It's posted clearly) and then I software tested it to +5/-5 so now everything seems slightly OOF to me . . . is it? No clue, I think it's observational bias, but I'm convinced I need to sell my 3 bodies and get a 5Dmk3.

My primes were all spot-on with the 5DmkII. So, I clutch my 200mm 2.8 II with a gollum-esque lust and insist that people are too close to take a good picture half of the time. ;D

Software calibration is a tool, so long as it doesn't run you.


----------



## Efka76 (Feb 4, 2014)

Neuro, thank you very much for your comments! I really appreciate that!

Few comments:

Regarding setup of light: of course I know that more light is better  However, that was a maximum that I could get today. In summer I will try to do testing during sunny day and will see what kind of results I will get. 

Thanks for valuable advices on Canon 50 mm 1.4 calibration! Deep in my mind I felt that insufficient light and vibration could cause such issues with testing


----------



## neuroanatomist (Feb 4, 2014)

Efka76 said:


> However, that was a maximum that I could get today. In summer I will try to do testing during sunny day and will see what kind of results I will get.



Add light.  Halogen work lights like this should be pretty easy to find, they're online and in most home improvement and hardware stores, 500 W and cost ~$20 here.


----------



## emag (Feb 4, 2014)

neuroanatomist said:


> Add light.  Halogen work lights like this should be pretty easy to find, they're online and in most home improvement and hardware stores, 500 W and cost ~$20 here.



Holy photons, Batman! I hadn't even thought of those! I have a couple but didn't even think of them when I was trying to AFMA my lenses. I sometimes use them for their intended purpose but more frequently just sit in the garage with them on during the short days to keep my head screwed on tight.


----------

