Making a focal reducer ? ?

i remember seeing a post somewhere about someone making a focal reducer from a lens out of a binocular? anyone have any info ??

this wouldnt have to be high high quality just something im messing around with

focal reducers seem very high priced and i just want to work out how one would be before i think of buying one im mounting a camcorder to the scope for lunar photography but get a lot of vigneting at unless i zoom in and then it gets too much magnification even with a 40mm lens

problem being i have a Mak with focal of 1540 and when i push it to zoom it ends up too much magnification

anyway any help would be appreciated

thanks

adam