I was hopeing this would work the way i suspected it might
my synta sight tube was a little crap in that it didn't fit snuggly and
the edge of the resess on the barrel was about exactly were my locking screw on the focuser wanted to do up make it in my case not entirely usefull.
So i had a go last week of making my own ( endless rain ) .. there was a lot of trail and error to decide how best to do this which I'll skip.
the tube is plain old 32 mm alli tube which of course won't fit your standard 1.25 " focuser. some time and a little work with some
sandpaper working evenly around it , eventually giving up at the slow progress and shelling out for a coarser grade got it just right and very tight in there.
The sight was a difficult choice and I changed my mind many times and rumaged through the garage over a few hours.I thought of the film canister lid early on but moved away as the caps i could lay my handson wern't at tight fit over the tube and didn't have any sort of centre spot which i could use to centre the hole .
much later in the day revisited the film cap idea again and found this cap , I'm not sure what brand it might be but the differance is its a male plug which tightly fits inside the ali tube its also centre marked .
Next bit most all cheshire sight tube combos have a diaginal cut to help with reflecting light back down the the tube pretty handy , but a little difficult to make , my feeling from reading a little from round the web was that in a moderately sized newt say 8 " and up its likely to throw enough light up the tube if you can bounce it back down .
The plastic film cap also helps here in that its underneath allows you to centre and glue a polished stainless washer.. just tried it out no problems seeng the centre spot, while not quite as bright as my cheshire its still easy to see and my backyards fairly shaded out at the moment
I've slotted for crosshairs but havn't got to that yet