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.

Simple.

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…..)

About canonrepair

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

6 Responses to Recementing of the 28-70 foggy element

  1. Jason says:

    Hi Ruzsa,can you tell me what type of your Zeiss focimeter?If I can’t buy the exact same model, what model can I buy instead? Does the Zeiss focimeter achieve the same results as those expensive devices on youtube?
    Grateful if you give guidance.
    Jason

    • canonrepair says:

      Hi Jason,
      in fact there are even better focimeters for this reason – the bigger the magnification, the better the result. (for ex LM-8 Lensmeter Topcon)
      I am sure, that my method with the modiefied focimeter is less precise than the rotative machines from the industry, but to build a rotational one is really complicated – I have a project, which I did not finished – the rotating aluminium table is placed on an old HDD from a PC, has the possibility of vacuuming, but even for that You need a focusable light sourse to light the middle of the lens with INCIDENT light (not from its other side) … and a telescope set to infinite, to observe the moving light spot – which you can take out from… an old focimeter 🙂

  2. mark schuster says:

    Really awesome idea. I guess the lensometer shows you the exact center of the lens elements for centering. Would be cool if you could cure the UV glue on the lensometer directly without having to transfer it. At that stage you would have something like this I guess:

    I would love to read more about your set up and the process behind it.

    Best,
    Mark

    • canonrepair says:

      The curing MUST BE DONE in the lensometer, without moving the parts (we are talking about 0.01 mm precision.
      This means, the curing is ALWAYS started in the lensometer, 120 sec for ex (this lamp is with fluorescent tubes – 36 watt power 🙂
      This hardenes the UV resin enough to be able to move it.
      On the picture you see the final curing. Just to be safe.

  3. gopecardoso says:

    Great work Janus…

Opinion, question?

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s