Canon 70-200 F2.8 IS – the good old glass

My customer has found it for a bargain price (no, in fact was not so cheap…) – but the lens has been dropped before.
I had to disassemble it, repaired the USM motor (see: refurbishing a USM) – and after cleaning and mounted the lens has a terrible resolution.

This lens has two adjustments, which could be done in the service: the shift adjustment on lens 13 from the group 5., and tilt adjustment on group 1.

The problem is, that you dont have access to group 13, as it is covered by an external tube, and by the USM motor.

Let try to adjust the lens with my favourite method: to get a symmethrical chromatic aberration , which means, case you look at a very bright light source on a black background, in the form of a triangle or a circle, with the lens in a slight defocus position, the sharp black/white transitions will be coloured in orange or blue. Case The lens is centered, the colour margins will be symmetrical. As a light source I use a cheap LED-lamp with a magnetic base (sold by Lidl), plus a mask made of a metal sheet or whatever you have with a perfect triangular or circular hole (3-5 mm).

As a first method I tried to adjust separately ONLY the group 5 – so I disassembled the lens – but to put it in the front of a camera is relly hard with the horizontal axis…

So, I had to make a holder of aluminium (covered with plastic tape), and the camera was positioned with the bayonet upwards. It’s a great help in ths my good old Zeiss lentgh measuring stand – 80 kg of cast iron, with movable and adjustable table. Is a green beauty.

1673995799478  1673995768989  1673995768870  1673995799504    1673995768961  1673995799518

The DSLR Canon was connected to my PC, so I could follow the picture in live mode.

By the way: at first I hade to determine the optimal distance to the cmos, as the lens element is NOT a full photografic lens, as a lucky thing, it is a positive lens (magnifier), and by playing with the cmos – lens distance I have found the correct one to get a picture from a target, positioned at approx 100 … 200 cm , as this is the usable hight in my workshop.
The target lamp was positioned on the top of a pole (yes, should be something more elegant and better, and…. I hade no time for cosmetics now), on a steel sheet, so I could position the lamp exactly above the camera.
As Yo see, works. The 3 screws which hold the element no. 13 (as I understood) are only to hold it in plane – but the fixing of the xy position is done by… a glue, or paint.
So, adjustment has been done, monted is the camera…. image was terrible.


Ok,  let’s do it with the whole lens. But how?!?!?
And when I took away the covering tube and the USM motor, I observed, thet the 3 screwheads are visible !!!
So, I repeated the whole thing with the half disassembled lens.

image004 (Egyéni)  image003 (Egyéni)    image001 (Egyéni)

So, now I can access the element 13 – but the lens MUST BE focused, and I have no USM..
I took a focusing lever from an another USM, monted with a rubber on the correct place – and set it to the slight defocus.
This time I used the circular target.

image0011 (Egyéni)  image0013 (Egyéni)

The 3 screws areNOT tightened, so it is possible to move the lens to get the optimal image.


After this, just fixing the position with some paint (nail varnish).

image0012 (Egyéni)

After mounting together the whole lens, made the test shooting – the lens is perfect!

Try it! (and drop me a mail, if workes)

Posted in 70-200 F2.8 IS Mk I, lens, test bench | Tagged | Leave a comment

Old Canon 100-400 meeting the new chinese milling machine

I have got an old Canon 100-400 – AF not working, one flex teared by the former technician. The biggest problem: the good guy destroyed the head of a screw, holding the USM motor – so I could not disassemble the lens.

And that is the moment, when You have to take a deep breath, and to mount it on the milling machine.
Canon lenses are NOT make to be mounted on milling machine. The debries could fall in the inside, and during machning, the lens can move on the table, and be destroyed. As a toll I used a 3mm full metal carbide end mill.
After disassembling I repaired the flex by soldering, as I had no parts for it.

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The Mistery of the 70-200 F4 Aperture

I have got a 70-200 F4, with a strange aperture problem: the aperture works, but not always.

After disassembly I realized, thet the aperture ring on the part moves not perfectly smooth (by a screwdrivers tip).

I disassebled completely. The rotor of the small stepper motor is made of plastic, and the axis (1 mm diamerer) was made of plastic also. And that part was broken.

I had an another lens on the shelf.

It was also broken. Exactly in the same position….

As i don’t have a new part, tomorrow i will try to make a new shaft of steel, and to drill a hole in the cilinder on a lathe.

Let we see the work….

And finally the 70-200 WORKS!

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Gentle cleaning of a camera? The shoe mud brush!

No, I am not joking.

The 6d plus a Tamron 100-400 has fallen yesterday in mud. For now the mud hardened, and the best way to clean it, before opening the camera was to clean it approx 45 minutes (!) with a brush in the backyard, with a brush which I use for my training shoes.

After this wiping with some wet clothes, immediate drying, blowing with compressed air…

And now I will open the body.

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Recementing of the 28-70 foggy element

The Canon 28-70 F2.8 has a special problem: after a while, one of the duplets inside gets foggy. The problem is the cementing, a bad glue or process.

After you disasseble the element, you can glue it with a UV curable adhesive.

Here is my device (built from an old Zeiss focimeter), and the UV curing procedure (with a Lidl nail maker set).

Some technical details:

The middle part is made of PTFE (Teflon), as should not destroy the lens, and should not be glued to the lens – as this happened first time, when I used an another material. Teflon is great!
The 3 small disks are also made of PTFE, and they have a small magnet on the base, so they can be rotated or moved on the polished steel ring.
In the middle of the PTFE ring there is a closed area, in which I can make vacuum (or more precisely, depression). This is made with an ejector, so I just have to switch on the compressed air with the small switch (is a pneumatic switch). I use approx -0,5 bar depression.
When the first lens element (which is a plan-concave one) is cenetered, I switch on vacuum. This holds it on place.
After this I put 1 drop of glue on the lens.
I put the second element (concex-concave) on it. I rotate the lens, to get out the air, and to have uniform glue distribution.
I adjust it to be centered with the lensometer.
When is in center, I set the 3 PTFE disks on the margins.
I recheck the centering.
Switch on the UV light.

That’s it.


By the way: I had to modify the lensometer, as originally was oblique, and MUST be vertical. That was a good job, to cut it. And LED lighting, of course.

I was waiting 2 years to get rid of the lensometer. Was about 45 EUR.
(Now I have 3 of this type, from a flowmarket, and a better one, a japanese Topcon. The Topcon was a bargain: 15 EUR…..)

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What is the pickled cucumber good for…

…in the camera workshop?!

Today I have to clean a Sigma 24-105 1:4 OS – inside/outside. (in fact, I hate Sigmas…).

First problem: to disassemble the front lens, I have to screw out the plastic ring – which has no holes for the tool. In such cases you have to use a cylindric tool, which ends in a rubber part, which grabs the ring through friction.

I dont have that tool. But fortunately, i have some empty bottles. I put some double sided tape on the edge, and .. voila! Works fine.

* by the way, don’t forget to apply 2 drops of alcohol on the thread. Helps a lot the unscrewing!

Posted in General topics | 6 Comments

USM refurbishing

Cleaning of the optical encoder ring helps only the focus hunting cases.
When the problem is with the usm ring, I refurbish them with degreasing, polishing both rings to get back the plane, shiny surfaces, then cleaning again, after which mounting together.
When mounted, you have to try to rotate the plastic/metal ring relative to the metal one. IT MUST have a high frequency sound. Case not, just rotate them, till you get that annoying noice. This brings together the surfaces very close, so they adhere to each other – and USM starts working.
Here you see my small polishing tool, made of an old HDD disk, which is the best plane, which you can get, and a battery screwdriver. Use some alcohol for moistening! Polishing paper: 2000.

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Eastern Egg in a 17-85 IS

I had to replace the aperture cable – and I found the former one too, which the other service did not removed before mounting the new one.

They dont like to disolder?!

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70d rotating LCD + 80D donor

I had to repair a faulty shutter in a 70d. (on the photo there is a mistake. It is a comparison between 40D and 70D curtain).

As I did not have a new one, I searched for a good curtain from anything else around…. and the curtain from a good, practically new 40d does fit perfetly!

Problem solved, mounting together, works fine…. excepting the LCD, which has a contact problem. In fact the camera has been disassembled before 2 times by somebody else… Never pull them by the wires.

I always HATED this rotatable LCD-s They have to last +1 day aftr warranty expires, and as I could find replacement on ebay… Not me is the first, who needs this part. 🙂

But is in China, and even using that I should solder back 2 tiny wires.

So, I searched in my scrapheap… and I have found an 80d, which has the same cable!…. but not exactly.

The two microswitches, which give the position information of the screen, are not there in the 80d frame. Shit.

This switches put the 2 wires on GND case they are activated.

So, I decided to put two extra wires between the main board and the LCD frame, and the GND (minus) wire from the LCD board (as there was no space for 3 wires in the frames hole).

And…. works!

Here is the GND wire.

By the way: the tiny wires in the flex cable are SHIELDED (!!!) wires.

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Damaged screw

Case You have to screw out a bolt with damaged head (after forcing a stucked screw with the screwdriver can happen to damage the PH00 slot), You have 2 possibilities: to cut a simple straight slot with a small grinding machine (little bit dangerous, but sometimes is the only possibility), or to grab the head with a side-cutter, strong enough, that the blade enteres in the screwhead, and rotate it.

Posted in General topics | 5 Comments