N/A Mystery diopter?

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Beeman22

Beeman22

Member
Jan 30, 2018
151
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Michigan, United States
Other than a Williams peep on one of my HW30's and the original FWB units on the 300s, I have virtually no experience with diopter sights, but I definitely like using them. So I recently acquired this for very little cost out of curiosity, hoping to adapt it to my Williams. No name that I can find, appears to have some magnification and a variable iris. The magnification adjustment works (the silver ring), but the iris appears to be frozen. No sign of rust or anything, but I can't make it move - at least, not yet.

So three questions:
  1. Anyone know who the manufacturer might be?
  2. Is there a trick to getting the adjustable iris moving again?
  3. What is the thread adapter needed to get the large metric thread adapted to the smaller Williams hole? Are these readily available for purchase somewhere?

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My understanding is that its an adjustable iris and diopter, which I can adjust by rotating the silver band. That part works.
And I can't believe that with as much time as I spent messing with this thing, I never looked at the eyepiece closely enough to realize it had lettering all over it! It's a Gehmann D75. The issue is that adjustable iris is currently set at 2.0 and appears to be rock-solid stuck there. Anyone ever have any luck messing with these?
 
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There are old adapters for Gehmann-Williams irises. They are very rare on eBay and are expensive.I have 2 irises with adjustable diaphragm, a new Gehmann and an old Haenel. I had some problems with the Haenel, I don't remember what exactly. I took apart the entire diopter and iris completely, washed, lubricated and reassembled. It has been working great since then.In order for your iris to work perfectly with the stock front sight and diopter insert on the HW30, you need to set the aperture to 1.5 mm.
 
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It's an older Gehmann iris with a 1.5x focusing/magnifying lens. As you discovered, the name and model number are stamped on the rear rim of the iris. The beauty of an adjustable iris is the ability to find the opening size that is the best compromise between clarity (smaller opening = more in focus) and light (bigger opening = brighter view) for wherever you happen to be shooting. Most factory diopter eye disks have an opening near to 1.0mm, which is great for a well-lit target range, but out in the real world a bigger opening is often useful.

The iris leaves do get sticky over time. Try a gentle clean with alcohol.

The adapter is just a simple gadget with the appropriate threads - male 7/32-40 on the front (typical US thread), female M 9.5mm on the back (typical German thread). Any place that sells target shooting goodies should have them. Mine came from Champion's Choice in Nashville several years back.

I have a similar iris, seen here stuck in a Williams sight with the adapter.

 
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