This article guides how to disassemble Rokinon 50mm F1.2 UMC CS X lens for cleaning dust in aperture chamber.
When you focusing with Rokinon 50mm F1.2 UMC CS X lens – whole optical core is moving forward/backward inside lens frame. Focusing is quite smooth and precise, however there is a side effect of such mechanical design. All the dust that may collect near the filter thread is migrating with air inside the lens frame.
If you attach 62mm lens filter or even lens cap and focus lens – air will more actively flow in front area.
I purchased this lens sample used, and previous owner shipped it carefully packed in large box filled with foam beans to protect lens from any damage (thank you!). Unfortunately lens was not wrapped into plastic bug, and foam was rubbing over focus ring texture producing a lot of white dust. When lens arrived it had huge amount of dust even under the lens cap. When I focused lens first time – white dust immediately migrated inside under the glass.
Good news is – it is quite easy to disassemble and clean Rokinon 50mm F1.2 UMC CS X lens : )
First step is to use JIS 000 to unscrew three bolts on the mount ring.
Pull the mount ring out, it is quite thick but made of lightweight metal alloy.
There is large set of infinity focus calibrating shims in my sample of Rokinon 50mm F1.2 UMC CS X lens, I like to see that because it allows to fine-calibrate lens for another camera if infinity focus is not precisely matching. Though on my cameras it works perfect and I don’t need to calibrate. So you need to accurately pull out all shims. Note – brass is capturing and over time memorizing finger prints, so use gloves during lens disassembly.
Then firmly grip the rear lens module and unscrew it CCW. There is thin thread displayed.
And… that is it : ) Now you have access to the aperture chamber. I’m using Rocket Blower to remove all the dust from internal glass surfaces and aperture blades.
You can then close the aperture and check if there is no dust on blades.
And check it from the front as well – looks perfectly clean now!
Now accurately position calibrating shims back, attach the mount ring and screw in three bolts.
Rokinon (and Samyang) 50mm F1.2 lens is very nicely built. More important – it is super easy to repair and clean this lens model due to simplified access to the aperture chamber and internal glass surfaces – like it is done in Carl Zeiss ZM series lens. All you need is to unscrew the rear glass module after removing mount frame. I like that simplicity of maintenance. It also brings confidence in use of Rokinon 50mm F1.2 – whenever it collects dust or moisture – it will be easy to bring it back to clean shape.