Close focus adaptor

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SteveD
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Close focus adaptor

Post by SteveD »

Can someone explain the optics of a close focus adapter?

I bought one and it works but the glass is of really poor quality so the sight pic is a bit blurry, the light pass through is not so good and it pinholes. I would like to understand the optics of close focus so I can buy a nice piece of glass from Edmunds or somewhere and make my own close focus adapter.

I also would like to be able to have it focus closer than 50 ft, say 15 or 20.
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SteveD
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Re: Close focus adaptor

Post by SteveD »

I got an answer on another forum.

A 'close focus adapter' is a fractional diopter lens, 1/4, 1/4, 1/2, mounted between the scope objective lens and the object being viewed. (Is that a coincidence?)

The focus distance of the close focus adapter is determined by the diopter power, the power of the scope and the distance from the objective lens of the scope to the diopter lens.

The diopter measurement of a lens is the reciprocal of the focal length in meters (one divided by the focal length), so 1 diopter = 1 m, 2 diopters = 0.5 m, 3 diopters = 0.33 meters, and so on.
Last edited by SteveD on Fri Jun 08, 2018 3:55 pm, edited 1 time in total.
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Jerry G
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Re: Close focus adaptor

Post by Jerry G »

I got mine from Leupold and it is a quality piece of glass. It works just fine. I can tape it to any scope I have and it works. Be aware Leupold has 2 different threads on the front of their scopes. Old ones vs new ones.
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SteveD
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Re: Close focus adaptor

Post by SteveD »

Jerry G wrote: Sun Feb 04, 2018 2:53 pm I got mine from Leupold and it is a quality piece of glass. It works just fine. I can tape it to any scope I have and it works. Be aware Leupold has 2 different threads on the front of their scopes. Old ones vs new ones.
I think the Leupold close focus adapter is for 50 feet, right?

I am looking for 15 feet for indoor dry firing.
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ywltzucanrknrl
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Re: Close focus adaptor

Post by ywltzucanrknrl »

Steve, I was able to make the 50' Leupold adapter work on a Burris scope by securing the 50' adapter in a piece of pvc that was big enough to slide over the front scope bell and then sliding the pvc with the 50' adapter secured in it until it came into focus and then securing it--with tape. I used it at about 25' in my basement for dry firing. The AO on the Burris scope would only go down to 25 yards---so this combination will work if your scope has an AO of 25 yards or less for a 25' focus. It was very clear and had a sharp focus.
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Re: Close focus adaptor

Post by Jerry G »

by SteveD » Sun Feb 04, 2018 5:03 pm

I think the Leupold close focus adapter is for 50 feet, right?

It goes sown much farther on an EFR scope. I have 2 adapters screwed together on a non EFR and shot at 10m with my air rifle.
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DavidABQ
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Re: Close focus adaptor

Post by DavidABQ »

It seems Mr. Jerry G answered my question prior to me expressing it.

Apparently you can stack those adapters to focus on a target at a closer distance than 50ft.
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