A few years ago, a gentleman sold me a Canon FD 300mm f2.8 L lens (Review here). He sold it cheaply only because there were haze on some of the lens elements. Despite the haze, I was already very happy with the image quality this "defected" lens delivered. So I didn't do anything about it.
During lockdown in 2019, I had too much time (and apparently too much wine), and wanted to take the lens apart and clean out the haze myself. Yet this is a valuable and great lens. I was afraid that I might damage it. After some googling (and more wine), I finally had the courage to carry out the surgery. Although I got confused at certain point, at the end I did manage to reach the lens elements that needed cleaning without damaging it. The lens is now fixed and happy making amazing photos.
Thinking it might be helpful for the future me, and other (sober) brave souls, I documented and share below the steps I took. But if you are not sure what to do, bring the lens to a technician!
The lens can be separated into three main components:
To remove the front protective glass, you have to first remove the glued-in rubber band on the built-in hood. The haze on my lens appeared only on the glasses in component II, so I needed not dig in further here, but I suppose it would be quite strict forward to gain access to all the elements inside component I after separating it out from the rest of the lens.
Carefully pull down the rubber grip band on the focus ring. It is quite tough, but no need to cut or damage it. You will find the 3(? Don't remember. Told you I had wine) screws that hold component I and component II together:
After removing the screws, it is easy to unscrew component I from the rest of the lens:
To unscrew component II from III, first remove the 3 screws on the white ring above the filter slot. They might be hidden under white paint on lenses in better condition as mine.
Now the 3 main components are separated. Carefully examine Component II from the side of the focus ring, on the edge of the lens element, you will find the gap of the metal spring that holds the elements in place. Since this spring is in direct contact with the glass, (this is the part where you better be brave and sober), be VERY careful not to scratch the glass while taking out the spring. I do not have a good solution here....Canon god bless you.
Thank Canon god...
Once the spring is out, the glass should drop out easily. The glass below is now also accessible from both sides. These were the glasses that had haze. So I stopped disassembling the rest of the lens at this point.
The glass looks like a beautiful jewellery after cleaning.
This is how the separated components looked like:
And then I reversed the steps to put the lens back together.
After cleaning the image quality did have a noticeable improvement. It feels like breathing in fresher air. Probably it is also because I was less drunk at this point.
I hope these information would be a good reference for anyone who desperately wants to disassemble his/her FD 300mm f2.8 L lens. But, again, if you are not sure what you are doing, bring the lens to a technician! Don't harm this wonderful lens.