Adjusting the coaxiality of the 3. lens group in an EF 24-105 IS USM lens

First of all: this is NOT an official method for adjusting the lens.

You will need this procedure after changing the aperture flex cable, or if You have a lens with not sharp image.

Changing the flex cable

If You have to repair a 24-105 aperture flex cable, take care that the aperture module is not intended to be disassembled.
It is possible to order the flex cable for it, but be careful with the dismantle of the front element of the aperture module.

Canon EF 24-105/4L IS USM Lens Review

Picture from here:

On the image the middle group is the aperture module, in fact it is the 3. from the left side.
This group contains the electronic aperture itself, an another mechanical  aperture and some lenses too.

If You disassemble it once, the lens will be no more aligned, which will cause aberration – for example chromatical aberration on the picture.

Here is the complete 3-4-5 group.


And here only the 3. group.


Pictures from:

Be careful – this video does not speak about the eccentric pins, and the importance of their position (they are on the left side of the table on the last picture).

The front lens of this group is not only fixed with 3 screws to the body, but it is adjustable with 3 tiny eccentric pins, when the 3 screws are untightened.

I believe that this operation (the optical alignment) must be difficult even in a professional workshop, in home conditions probably impossible – but if You look to this small adjustment pins, You will see, that they have a marking point on their head.


That point marks the thinnest (minimum) point of the excentric.
Make a sketch with the original position, then take them out from their hole. They are simply pressed in the plastic. You will need for the adjutment a hexagonal (allen) key.


24-105-2 24-105-3 

If You put the eccentric pins exactly in the original position, you have 50% chance to get the lens in the right position: yes or no….
Ok, it depends, how precise You work too. But if the pins were forced in the past – this was last time in my case – then they will not give a well determined position to the front element. And the photo will have chromatic aberration, and not a sharp image, as this lens should give.


The procedure

(I dont know what is the factory method. I only know, that if we adjust the pins, the lens will occupy a lot of positions, and its axis will match the axis of the rest of the lenses in only one position. So we have to find that one

To control the image (the photo) is possible, when the lens is assembled.
To make the adjustment, is possible only, when You have full access to the pins.


There is still a way to fulfil both conditions: to assemble the lens without the USM focusing mechanism and without the electronic board, and to turn it to the 105 mm zoom position.
This is the only position, in which You will see the eccentrics through 3 holes made for this reason.

At first, You will have to loosen the 3 screws, which fix the adjustable ring with the lens.
Then bring the 3 eccentric pins into their middle position. The have a making point on the head, that should be toward the front of the lens. (this is to start with adjusting from the theoretical concentric point with the barrels axis)
Now You have to assemble the lens without the USM module, and without the electronic board.
The focus lever is loose now, so you have to fix it for ex. with a rubber ring, or with adhesive tape (as we will se later: in the infinite focus position.)
Now put the lens on a camera. You have now a perfect manual lens, at maximum aperture.


Zoom to the tele position.

We need now a shiny regular object at the infinite

You have to make an artificial infinite object.
I used for this an old film camera, putting instead of the film a matt plastic plate, on the middle of which I glued a black foil with a hole in he middle. Important is, that the hole MUST have perfect sharp edge. Behing I placed a sheet of paper, and a very strong white LED light source.
In the camera I mounted a 200 mm / F4 manual lens (NIKON :)), rotated on infinite position.


If You look at it from the front, You will see the picture like it would be at the infinite distance.
So, if You look at it from the front with another camera, and You use the autofocus, the focusing will turn the lens to the infinite position.


Here is the focus lever, fixed with some rubber rings.


And here is the hexagonal key.

But now You have NO autofocus on the tested lens, so You have to turn manually the focus lever till You see the image very clear in the eyepiece.
With camera with liveview is much easier.
If You take a photo, You will observe, that the shine white circle has a blueish coloration on one side. This is the sign of the bad alignment.


This was the first picture, after assembling, before adjusting. (visible problem on the left side)
Now try to rotate the eccentric pins (possible ONLY in 105 mm zoom position), till the blue collar dissapears. This is possible perhaps only after adjusting all of the eccentric pins.


This is on intermediate position. (problem moved to the right side)


And this is the final picture.

When You are ready, tighten the 3 screws.

After this, try to make a shot on a distant object (200-300 meters), which has the sky behind (having  a strong contrast).
If the adjustment was OK, You will get a sharp picture, with no chromatic aberration.

The hole thing works only, I the lens is not misaligned for example on the 5- group (the lens which is on the camera side)
NEVER loosen a screw which is glued by the factory – only if You are sure, that You can adjust it correctly.


If You can’t do it, drop me a mail.


(any text, figure, photo from this article is made by me
– excepting that one which are special mentioned –
case You use it somewhere I appreciate, if you mention the source )
© canonrepair

About canonrepair

Ruzsa János. Amatőr fotós, Canon DSLR váz. Amateur photographer. Canon DSLR user.
This entry was posted in General topics. Bookmark the permalink.

65 Responses to Adjusting the coaxiality of the 3. lens group in an EF 24-105 IS USM lens

  1. Hey!!!

    This is so cool, finally found a place where i can get a guide!!

    I hope you can help me through this…

    So i got this 24-105 canon L, and the photographs, they look blurry at the edges.

    can i send a picture? and maybe how i can fix it?

    Thank you very much

    • canonrepair says:

      Hi,sorry for the late reply.
      In this lenses you have some spacers or washers between certain lens elements. The reason is, that in the factory they adjusted the lens in the optimal position, to get the focus of a plane target (which is projected by the lens to the plane of the CMOS) at the same distance for the middle and the corners. If somebody disassembled the lens, and has forgotten to put back the washers, you could have this problem.

  2. Maxi says:

    Hi, thanks for the explanation. I have a question. When you refer to the 3 screws to loosen prior to calibrating the allen screws, and then to adjust … I’m not sure which screws it is.

    • canonrepair says:

      It is funny, as at the moment I dont have a disassembled lens, and not even a photo. The lens element, ewhich you can shift with the 3 excenters is held by 3 screws with relative big head, and some elastic washers. Case that are tightened, you cannot adjust.If they are loose, the lens element can move after adjustment. So, if you make the 3 washers a little bit stronger (by bending them with a pliers), they will act on the adjusted lens element, to hold it on place.
      For example, you can tightene them 100%, after which loosen back with for ex. 1/2 turn.

  3. Robert A. says:

    Your explanation concerning focus alignment was very informative and much appreciated!
    Question: at 105mm, the infinity point is approximately 21m. I’m not quite sure how you managed to make the adjustments and setup the lens. Perhaps a video dedicated to proper alignment would be most excellent to do! Since I have not seen any videos provide of such a demonstration, it would certainly be a ‘first’! Furthermore – vital – since many lenses with the ailing replacement cable procedure is sure to ruin accurate focus – rendering them all useless.

    • canonrepair says:

      Hi Robert,
      if the infnit is not at the infinite distance, You have to reduce the thickness of the bayotett ring.
      Calculating with the formula from the geometrical optics, 1/obj +1/img = 1/f you get with your data a difference of 0.527 mm, which you have to eliminate.
      Are You sure it is the original bayonett of the lens?
      What about the vidio…. Yes, case I will have time, I will do it.

  4. abbas says:

    can you make a video please please 😀

  5. Antonio Mauricio says:

    Perdi um colare do istaberizador da lente Canon 24 105 Será que pode me enviar local que possa adequerir os 3 colares estabelizadores e os parafusos e colares do diafragma dado que estão em pessimo estado por tentar rodar.

  6. Antonio Mauricio says:

    Oi eu desmontei minha lente canon 24 105 para substituir flex segui seu vidio com extrema percauçao. Depois de substituir o flex fui montar e nao reparei que os colares do estabelizador eram diferentes dos diafragma. Depois vinho a saber que eram diferentes tentei colocar no citio certo mas me parece que o diafragma não se move em toda a sua extençao está perre .será que tem algum ajusto Perdi um parafuso de um desses colares será que pode me dizer onde posso comprar esses colares e parafusos.dado que os originais estão em pecimo estado por tempar rodar Atenciosamente Mauricio

  7. Robert Foo says:

    “ At first, You will have to loosen the 3 screws, which fix the adjustable ring with the lens.
    Then bring the 3 eccentric pins into their middle position. The have a making point on the head, that should be toward the front of the lens. (this is to start with adjusting from the theoretical concentric point with the barrels axis) ”
    I hope this blog is still open and if not I hope it can be revived as this issue is more relevant now as this lens is now quite a few more years old.
    I brought this as a used lens and feel totally cheated as the seller did not mention the lens was not sharp any longer. He refused to respond to my messages. So I will diy to recover some losses.
    I have stripped down my lens as it is not giving sharp images at all. A shot of lights at a long distance shows them looking “smeared” to one side like your pressing the shutter and moving the camera left. That’s on live view on a tripod.
    Anyway, your instructions I am not clear of which three screws and what is the eccentric pins. I losened many screws removed the hex pins but could not get anything to move except the zoom barrel. Hope you can still help.

    • canonrepair says:

      if we number the lenses from the front, the 1. (first) is front lens, 2. the focuslens, and the 3. the lens in the inner barrel. Take out 1 and 2. Then you will find 3 screws on the margin of it. Accesible from the front.
      If you untighten them 3/4 turn.
      Now from the side of the barrel you can adjust the 3 screws. (only in a certain barral position.)

  8. BDK says:

    hi. If you need to replace 2.nd lens group, but haven’t dissembled the 3-5th lens group do you need to do this calibration?


    • canonrepair says:

      if you repair a 24-105 lens, you ALWAYS have to check coaxiality, even if yoh did not touched it.
      and case it is good, be happy.
      case not – adjustment.

  9. ajsjabbal says:

    Hi, It’s wonderful. I discovered this method three years before and already using in my repairing shop in Delhi.
    I am new in this group and my eyes get widen when I see your same method.Great, hungarian friend.

    • canonrepair says:

      Hi, this is great. Could you send me the homepage of your shop? (I am only a part time job freelancer, so my workshop is a kitchen table only…)
      Send it to my email:

      • Vi Tran says:

        I replaced diaphragm on my 24-70mm F2.8 L lens. Now, it has the same problem as you described for 24-105mm F4 L lens. Do you have any way to adjust this 24-70mm F2.8 L? I found 3 eccentric pins ( with screws in middle) but I do not know how to set it up. Please let know if you know how to do this. Thanks in advance.

      • canonrepair says:

        make a photo about the excentric pins pls. anyway, you can adjust the lens only in a position, when the excentrics are visible and available

  10. fflashcell says:

    I leave the cameras face to face?

  11. Hugo says:

    i have a big problem. Bought the lens new back in 2007. as soon as i received it, it was soft so i sent it to CPS NL to calibrate but found out there were some problems with it. they did repair the lens for free and it arrived much better, so i was happy with it. Now i got error 01 and when i asked a technician to replace the flex cable, we found out that the lens was missing the 3 tiny eccentric pins…. He told me in his +30 years of experience never saw a lens without them. How could they mange to calibrate the lens without those pins? how did they forget to add them back after adjustment? To make matters worse, the CPS center (ETBass) has declared bankruptcy some time back… do you know where can i get those pins??? i just hope that after assembly there is no need to recalibrate but i doubt it will be ok. not sure what to do now…

    • canonrepair says:

      unfortunatelly that pins get loose sometimes. In that case you HAVE TO fix them with some glue, otherwise they will fall out. Normally the moving lens is fixed with the 3 screws and flexible washers, and adjusted with the pins. In the past after adjustment I always disassembled the barrel, and tightened the 3 screws, so the lens element was holded in the correct place AND fixed by the screws too. This was unnecessary, but very secure. Now before adjustment I hand-tighten the screws, then I turn them back 1/3 rotation, and the flexible washer hold the lens in a sufficient strength – so no full tightening is necessary after the operation.
      But you could use this for working without the original pins. Just borrow 3 pins from an another lens, do the adjustment, tighten the screws and after this take out the pins. Thats it!

  12. canonrepair says:

    Nowadays, as I told I use a simple very bright WHITE light source, like a homogenous LED panel or bulb, on which I put a black triangle, of approx 1x1x1 cm. Or, You can use a black board, with the sam triangular hole. Or a perfect circle of 1 cm diameter. In this case the distance is about 1 meter to the lens, setted to the longest zoom position.

  13. sorry is a 0.9 mm torx ?
    regards Marco

  14. Ray says:

    Hi, I just replaced my aperture and would like to know, what is the size of the allen key needed to adjust the eccentric pins? Thanks!

  15. Martynas says:

    Cool post! Good sort. 🙂

  16. canonrepair says:

    If you mean the hole on the black film, I used one whith 2 mm. Important is, to have a good edge, which gives you a sharp image.

    • Martynas says:

      Thanks for answer. I get a black film with 8mm diameter of hole. I have Olympus old camera and vivitar 400mm f5.6 lens. I tryed to make photo with Canon 50mm f1.4, Canon 70-200 f2.8, Tamron 17-50mm f2.8, but results are unclear.
      There are my photos:

      Question: are all my tested lenses in perfect condition or not?


      • canonrepair says:

        I think Your lenses are OK from this point of view. Normally I always make more pictures with the same lens, and it’s a good ideea to take picture a little bit out of the best focus, to get the chromatic aberration, which tells You the coaxiality: if it is symmethrical, the coaxiality is good.
        In the last time I use a very simple target: a bright white surface (a fluorescent tube), in the front of which I have a black square of isolation tape. I just take a picture in the lagest zoom position (105 mm with a 24-105 lens for example), and is as good as the method with the artificial infinity with the sacond camera.

  17. Martynas says:

    What diameter of hole? Thanks.

  18. thomas smith says:

    hi have you an adjustment system to adjust the eccentric collars holding the stabiliser lens assembly.? no one seems to mention these eccentric collars. regards thomas

    • canonrepair says:

      unfortunatelly not.
      normally you don’t have to dissassemble it.
      I think, You should use it as a single lens in a projector, and to adjust it till the projected image is is the sharpest.

      • thomas smith says:

        hi thanks for reply,you have to remove these collars when replacing the diaphragm flex.they are the first set of collars from the rear of the lens.they have slots for special adjusting tool.i normally mark them and keep each collar in its original slot.i have a lens that client tried to fix himself.not quite sharp.there are also eccentric pins on rear element but there is no need to adjust you say use it like a projector lens.regards thomas

  19. Adam says:

    I have a problem with my 24-105L. When I take a picture of a flat object, for example a newspaper on a wall it’s plain to see, that the sharpness is degraded in left-down corner and right-up corner.
    Picture quality in the center and the other two corners is very good and up to my expectations. This problem is especially irritating @24mm F4 – even stopped down to F8 sharpness in the two corners is degraded. @105mm I can see a only a little, acceptable sharpness degradation in the left-down corner. After switching to manual focusing I noticed that the loss of sharpness is caused by front focus in the left-down corner and back focus in the right-up corner.
    Something is obviously misaligned in my lens and I’d like to fix it. Any suggestions? Where should I look for calibration points for that isue?

    • canonrepair says:

      as You know, the lens mount (bayonett) is hold by 4 screws, and standing on 4 protrusions. If anytime the lens was falling down or forced, then the screws can bee loose, ore even the munt can be deformed.
      The explanation of the difference between 24 mm and 105 mm zoom position: at 24 mm the whole travel of the lens is a few mm on the full distance range, by the 105 mm is much more – that means the same thickness difference on one ore other side of the lens makes more relative focising error at 24 mm focal length as on 105 mm focal length.
      Try to put some (1 or 2) washers under the bayonett.

      see this: (in hungarian, but not very difficult :))

      • Adam says:

        Thank You for a quick and a very good advice. One single washer solved my problem. I wouldn’t think that this could be so simple! 5 minutes of labour and I get sharp images through all of the frame at all focal lengths. I’m really happy with my lens again 🙂

  20. canonrepair says:

    no, no washers. The alignment is adjusted with the excenters. You have to rurn them, till the picture will have no flare on any side.

  21. Olek says:

    Im wondering if I could change the flex tape buy mu own. So I d like to ask some questions. Is there a possibility to get to the flex tape solder pionts without totaly dismounting 3rd group, I mean without screwing those 3 so important excentric pins. If its possible what is the chance that my lens will be sharp and good quality, if I put all the ellements back together as they were before. Or its not possible without further calibration the way you described in the article and then in the comment concerning af callibration? Thanks for the article.

    • canonrepair says:

      Definitely NOT. You have to disassemble it before soldering. Anyway, a lot of times this lenses are already misaligned (dropped down before for example), so they need adjustment.
      if You will not be able to make it 100% good, you can send me Your lens, and i can do it for You for a reasonable price. i suppose you are from Poland – transport is not a problem.

      • Olek says:

        Thank You for quick reply.
        For the same reasons you wrote at the homepage, i would like to repair the lense by my self, and I’ve read too many bad opinions about the polish canon official service, especialy when it’s about lens repair. I would rather send it to You. But I stil think i could do this alone. Making artificial infinite object should not be the problem with my old Exakta, so the aberration i should be able to set correctly. But im a leatle worried about autofocus. In any videotutorials how to dissasemble and assemble the 24-105 there is no aberration aligment made (thannks to you i know it’s a fault), neather autofocus alligment. Should it work sharp as it was before without any allignmet? If not, what’s the method to allign the autofocus? (is that what you wrote to Simon, with the washers?) Thanks for your help.

  22. ray says:

    Can you explain to me this in layman’s term:

    “We need now a shiny regular object at the infinite
    You have to make an artificial infinite object.
    I used for this an old film camera, putting instead of the film a matt plastic plate, on the middle of which I glued a black foil with a hole in he middle. Important is, that the hole MUST have perfect sharp edge. Behing I placed a sheet of paper, and a very strong white LED light source.
    In the camera I mounted a 200 mm / F4 manual lens (NIKON ), rotated on infinite position.”


    “If You look at it from the front, You will see the picture like it would be at the infinite distance.
    So, if You look at it from the front with another camera, and You use the autofocus, the focusing will turn the lens to the infinite position.”

    • canonrepair says:

      if You want to do the adjustment at a low budget, then take a fluorescent lamp (which has a uniform light), put in the front a white screen (glass or semitransparent plastic), and make a small square of a lack adhesive tape ca 3×3 cm – and fix it on the surface. this will be a good target from 1,5 meters, for the 105 mm zoom position.

    • canonrepair says:

      imagine that You have a normal film camera, You point it to an object at a very big distance, and if this camera is focused to that distance, on the film You will get it’s image (reversed, of course).
      The whole thing You can do reversed too: put a film in the camera with figure on it (a letter or a cross sign), put a light source behind and focus it on the wall. You will get a sharp picture on the wall. If You turn the lens to the infinite mark, You will get a sharp picture at the infinite (at a very big distance.
      You can watch now in this camera from the front with an another camera – and if You set the focus on the second one, you will have to set it on infinite.
      this is the method

  23. ray says:

    thank you for this link… i will try to follow the best as i can… my lens now is not sharp.. will try to calibrate…

  24. Simon says:

    Thanks! That looks much better. I can get a sharp point now.
    Looks like i did not mess up the lens, Looks fine as far as i can tell.
    Do you have a hint how to adjust the first lens group? When i understand it right,
    adjusting the first element (3 screws tilt) will adjust the “eveness” of focus?


    • canonrepair says:

      the 1st element is the front lens.
      at first, You have to adjust the infinite for the 24 mm zoom position. Look into the collimator, or a chimney very far from You. The marks sign should be on the smaller edge of the infinity mark. if not, You have to put more / less washers under the bayonet. You have to think on 0.01 steps of course… After this, turn the zoom to 105mm, and actuate the autofocus. Normally the marking sign must be in the same place. If not, rotate the front element. Aftre this repeat the whole adjustment.
      that’s all.

  25. Josh S. says:

    do you know how to fix the lens creep issue with this lens? There is a lot of misinformation on the web.

    • canonrepair says:

      if You mean the fcus creeping – that could be a problem of the ring USM.
      If the zoom creeping, I think there are two possibilities: to use other (bigger)rollers in the barrels guide, or to use some special tacky, high viscosity (e.g. Nye) grease under the zoom barrel, to break it’s movement.

  26. Simon says:

    I tried to repeat the procedure with no luck…

    I tried an old 500mm “supertele” f8 and a 200 f3.5 Telear Lens.
    I did put a endcap on them and drilled a small hole in the center. Then i attached
    a tin foil with a tiny hole on top of it & added a LED lightsource.
    When i look into that lens with another lens (tried different ones, 50mm f/1.4, 17-85 etc)
    on my 50D it will autofocus between 10 or 50m.
    When i move it more towards infinity or closer the image gets more blurred so the focus is right.
    I also tried to move the endcap further roughly where the film used to be on old cameras – no difference.

    What is your distance between the lens under Test and the “infinity simulator”?
    Any other hints?


    • canonrepair says:


      You need on old film camera, and the target should be exactly in the place of the film. You have to take out the shutter.. If the collimator lens (the 500 mm) is setted exactly at the infinity position, this projector makes a sharp picture at the infinite – that means the light beams come out parallel. This means Your second camera (which You want to test) can be at any distance (infinite is infinite) – but if You stay at a longer distance, the picture will be visible at a smaller angle, so the picture on the cmos will be smaller. So the best is to hold the camera close to the “collimator”, and now You can adjust the tested cameras lens – normally the focus will be alsa at infinity.

  27. Etienne says:

    Hi. Question: how do you use the camera to create the image at infinity for calibration? Are the mirror and shutter not in the way of your matte when you look into the lens?

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