bj Posted January 26 Share Posted January 26 Hi Im taking apart this Cooke 25-250 MKI zoom and can't figure out how to take the front element out. There's no threaded retaining ring holding it in place. Has anyone disassembled this lens before? cheers! Björn Link to comment Share on other sites More sharing options...
bj Posted January 26 Author Share Posted January 26 Link to comment Share on other sites More sharing options...
bj Posted January 26 Author Share Posted January 26 Update: There is a threaded retaining ring with two slots in it but its blocked by the outer front part of the lens and I cant figure out how to losen it. I guess its screwed on but there are no locking or set screws in it. Link to comment Share on other sites More sharing options...
Premium Member Dom Jaeger Posted January 26 Premium Member Share Posted January 26 Do you have experience working on cine lenses? Link to comment Share on other sites More sharing options...
bj Posted January 26 Author Share Posted January 26 Hi, very limited knowledge ? Its a pretty beat up lens so I dont have much to loose… The zoom group (?) of lenses are a bit loose on the guiding rail so I thought Id open her up and have a look. Link to comment Share on other sites More sharing options...
Premium Member Dom Jaeger Posted January 26 Premium Member Share Posted January 26 Yeah that’s not an easy lens to work on. The entire zoom group mechanism removes from the rear, not the front, and it’s a complex beast that is tricky to reassemble and calibrate even for an experienced lens tech with a lens projector and a collimator, let alone a novice. But if you don’t mind destroying a lovely vintage optic as a learning experience, I guess go ahead. Link to comment Share on other sites More sharing options...
bj Posted January 26 Author Share Posted January 26 Thanks for the info Dom, do you think its worth sending it to a lens tech after all? I might put this project on pause then… Link to comment Share on other sites More sharing options...
Premium Member Dom Jaeger Posted January 26 Premium Member Share Posted January 26 Is there an issue with the image? Do you get image shift or focus backlash when you adjust the zoom? If not I’d leave it be, otherwise maybe see what a tech says. It could be beyond repair if it needs parts that have worn, or be too expensive for what it’s worth. Link to comment Share on other sites More sharing options...
bj Posted January 26 Author Share Posted January 26 Yes the image shifts when adjusting the zoom and the entire zoom lens group essebly slides about 2mm on the guiding rail when I tilt the lens back and fourth even though Im not touching the zoom barrel. I can zoom the entire zoom range. It produces an ok image in focus. Link to comment Share on other sites More sharing options...
Premium Member Dom Jaeger Posted January 26 Premium Member Share Posted January 26 Ok, sounds like something loose rather than worn, so probably fixable. If you can find a tech familiar with these zooms it would be advantageous. Link to comment Share on other sites More sharing options...
James Ewen Posted February 2 Share Posted February 2 I had my copy of this lens serviced by Agis Loukas at One Stop Films in London, he did a great job. Link to comment Share on other sites More sharing options...
bj Posted February 2 Author Share Posted February 2 Thanks for the tip James, my zoom had two worn out followers in the zoom group so I made two new bushings out of delrin plastic. The MKI is kind of fun to work on because the lens splits in half and you can work on either the focus or zoom ? 2 Link to comment Share on other sites More sharing options...
bj Posted February 5 Author Share Posted February 5 So I tested the lens today after putting it back together and is was kind of spot on! Might need a shim or two for focus. BUT the focus is a bit stiff so I need to get into the focus part too. Does anyone have a clue how to get the front part of the lens (2nd pic in the first post) of the housing? It looks like its screwed on there but cant get it loose. Hm… 1 Link to comment Share on other sites More sharing options...
bj Posted February 6 Author Share Posted February 6 Update: So I got the front rim off by using one of those tools you use to change the oil filter on your car ? I also got rid of the vignetting in the corners on the widest focal length. Next is fixing the stiff focus so cleaning and relubing the focus threads I guess. 2 Link to comment Share on other sites More sharing options...
Travis Shannon Posted February 6 Share Posted February 6 I personally am loving the updates on this thread, great work dude. 1 Link to comment Share on other sites More sharing options...
bj Posted February 8 Author Share Posted February 8 Thanks Travis, Its the first zoom lens that Im taking apart so not sure how it will end up. Time and patience... ? Link to comment Share on other sites More sharing options...
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