unusual thingy please help

[Paduan]

hi this may sound stupid but i have a thing that fits lots and is useful for nothing i believe that it is some sort of imaging barlow but it only fits an old Yashika screw mount adapter. it came with a second hand C8 i purchased. looking through it ,it appears to halve the image size, as in not 2x but 1/2x i have screwed it in to my 8x50 finder and i cannot focus it i have added some pics of the ends. please excuse the dirty fingers i am working on the car

[Sylvain]

It looks like some kind of extension tube.
But could you take a picture of the ends?

[multiweb]

Could it be an eyepiece projection adapter? I have a WO 28mm that I used with a DSLR a long time ago. Looks a bit like this.

[torana68]

Unitron made one that looks similar , you dont look through it the image come via it, if that makes sence....(ie your using it back to front)

[Paduan]

sorry what exactly do you mean by eyepiece projection adapter? is it possible that it is some sort of anti vignetting tool?
Maybe i should post it in the non beginners section!

[Paduan]

you are on the right track it screws in "backwards" ie the lens end goes into the extension not coming out like a normal ep but what does it do?