It took some time to discover how to disassemble this lens from the front area and get access to the aperture. I think it’s most fragile area in the lens and may need repair, so good news is that getting there is relatively simple and doesn’t require optical calibration after assembly.
First step is to unscrew the front plate with lens lettering. I’m using thick rubber ring to do that.
You may want to unscrew the black fastener ring from the first lens like I did, but it’s not required, so skip this step.
NOTE: you can see the deep and rough paint scratch in the left border area. It’s intentional factory mark of the front lens group radial position. When assembling lens back remember to put it in the same way so two scratched marks fit.
Remove three black screws and front barrel can be taken off, unveiling access to the front lens group.
At this stage I also unscrewed large black bolt from the aperture ring and took it off. When assembling it back, that long bolt should fit back to aperture control area, which you will see on the very next shot.
Gently pull out front lens group (now you can clean it if required. You will see the aperture assembly, and the controlling area for the unscrewed long bolt is on the right side here.
Looks like all glass is secured with glue there.
I’ve also removed aperture fastener to have closer look at the blades (and clean them if required).
That was quite simple disassembly. The parts inside are not super fine machined, but they look durable and do their job great. I generally like how the lens is constructed and feel happy I can easily repair or clean it if required.