Film-Tech Forum ARCHIVE: Modification of Red Ring scope lens

This is topic Modification of Red Ring scope lens in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Jim Spohn (Member # 1547) on 11-11-2005, 04:55 PM:

Can someone tell me how to modify a Red Ring scope lens adapter so that it will adjust down to a 10' throw. I have facilities for machining. Thanks in advance for any help. Jim Spohn

Posted by Mark Gulbrandsen (Member # 72) on 11-11-2005, 05:29 PM:

Jim,

First note that its not necessary to remove any glass elements from any of the barrels themselves, but they do need to be carefully covered over!! Removing the actual glass elements fromr either barrel renders the lens worthless. Proper aligmnent can no longer be accurately done on these older lenses once the element positions have been disturbed!!

Have done quite a few of these and I can say that it probably won't go down to 10 feet, but it should make 12-15. It entails removing the front element group sliding barrel and facing the main(stationary) barrel and if need be the back edge of the sliding front element barrel length a tad bit shorter. This allows the element groups to come closer together to work at shorter distances. Once the barrels are shortened file the alignment tabs length down so they can slide further in the slots they ride in towards the back of the lens. I've never had to lengthen the slots but dong so "might" just get you to 10 feet if there is enough sliding barrel to remove. No definate formula for this.... just take some off the length and check it and see how minimized the astigmatism is, repeat if necessasy being somewhat judicious as to how much you remove at a time.

Also, The sliding front element group assy. will usually only align(go back in) one way... I've seen the slots offset just slightly on most lenses, some are marked with one dot and then two dots but in my experience but it wouldn't hurt to place a slight scratch on one side of both the stationary and sliding barrels to guarantee the same alignment which is so very critical to good resolution.

Mark

Posted by Pete Lawrence (Member # 130) on 11-11-2005, 09:25 PM:

The Film-Tech Magic Answer Machine brings up this thread from 2002.

Posted by Jeff Stricker (Member # 224) on 11-12-2005, 07:10 AM:

I've done one of these. Not easy with my limited tools, but it worked. As Mark says, put a mark on the pieces before taking them appart. If you get it back together wrong, it won't work worth a darn.