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Need assistance with custom projection lens (KO-120)
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PostPosted: Sat Feb 12, 2022 4:34 pm    Post subject: Need assistance with custom projection lens (KO-120) Reply with quote

Hi Everyone:

I am trying to figure out a way to attach a filter to a modified projection lens, actually a hybrid of the KO-120 and an unidentified lens. The front portion of the barrel comprises the KO-120. I have had advice from a Russian fellow who said his KO-120 accepted an M72x0.75 filter size. But he later suggested that his version might have been modified (ring shaved). I have tried a 72mm step up ring and a 72mm step down ring, but neither fits on my unit. Any suggestions? Are there adapters with clamps that may be used to fit a standard filter on lenses that have uncommon thread sizes? I have attached three images of my lens. Any help would be appreciated! Thanks!

-Charles





PostPosted: Sat Feb 12, 2022 5:35 pm    Post subject: Reply with quote

There are many screw-in and clamp-on filter sizes and adapters. In any case need to measure thread size and/or outside diameter. Inexpensive calipers will be accurate enough. A ruler can be accurate enough.

Click here to see on Ebay


PostPosted: Sat Feb 12, 2022 10:45 pm    Post subject: Reply with quote

visualopsins wrote:
There are many screw-in and clamp-on filter sizes and adapters. In any case need to measure thread size and/or outside diameter. Inexpensive calipers will be accurate enough. A ruler can be accurate enough.

Click here to see on Ebay


That's great. Thank you very much for the suggestions! The outside diameter is 75mm. Can you suggest where I can get the clamp on adapters? I checked around and there doesn't seem that much available.

Thanks again,

-Charles


PostPosted: Sat Feb 12, 2022 11:00 pm    Post subject: Reply with quote

Try ebay and google https://www.ebay.com/sch/i.html?kw=75mm%20clamp-on%20lens%20hood and https://www.google.com/search?q=75mm+clamp-on+lens+hood


PostPosted: Sun Feb 13, 2022 7:21 am    Post subject: Reply with quote

visualopsins wrote:
Try ebay and google https://www.ebay.com/sch/i.html?kw=75mm%20clamp-on%20lens%20hood and https://www.google.com/search?q=75mm+clamp-on+lens+hood


Thank you so much!


PostPosted: Sun Feb 13, 2022 3:13 pm    Post subject: Reply with quote

That is probably no thread you are looking at, but the anti-reflection grooves on the inside of the lens retaining ring. Sometimes that is made by cutting a (helical) thread, sometimes they are just parallel grooves.

In any case, if a filter needs only a temporary fix then a roll of black insulation tape can be your friend.


PostPosted: Sun Feb 13, 2022 4:12 pm    Post subject: Reply with quote

RokkorDoctor wrote:
That is probably no thread you are looking at, but the anti-reflection grooves on the inside of the lens retaining ring. Sometimes that is made by cutting a (helical) thread, sometimes they are just parallel grooves.

In any case, if a filter needs only a temporary fix then a roll of black insulation tape can be your friend.


Thanks, Mark, that makes a lot of sense. I think you are right: they are anti-reflection grooves. I am looking for a more permanent solution than just with tape. I want the filter purely as a protective shield for my front element.

-Charles


PostPosted: Mon May 30, 2022 11:22 am    Post subject: Reply with quote

In similar situations (when I've not cared about maintaining 'correctness' or resale value) I've epoxied a step-ring to the front of the housing. If your front barrel diameter is 75mm, you might try this:
https://www.ebay.co.uk/itm/153311134527