Back in the days of film cameras.

Sorting out things to throw away I came upon this little contraption. It was made before I could afford to purchase a Minolta Ring Flash 80 as it was then called.

You took two pieces of wood about the thickness of floor boards.

Take them to a friendly carpenter with access to a router.
Get him to cut a 45 degree angle slot in each side.

You then got hold of a half plate slide and cleaned it of all emulsion.
Slides were to be preferred because they were made of bubble free glass and were of good quality.

Putting some binding tape on the forward edge you placed it in the slots cut by the router. Then measured carefully and cut an odd piece of hardboard to the width needed.

The front of the box had an opening left the size of the cut slot.

When it was fastened together the slide glass could be slid down into the slot.

Now the law of  light refraction says the any light hitting a reflective surface will leave that surface at the same angle as it struck in the first instance.

Therefore any light striking the glass will be reflected at 45 degrees if it hits at 45 degrees.

In this instance I was photographing an old coin of George III. 

The light of the flash came off the glass perfectly even and as 50% of the power of the flash.

There is a slight distortion of the sizes but nothing too uneven.

It could easily have been corrected when editing, but was hardly worth the bother.

The main thing was to get the light from the flash to hit the piece of glass at the right angle.

For this I used a pot of jam which was the appropriate height. The interior of the box was painted a matt black to stop any unwanted reflections and the box worked well for photographing small finds from the Romano British digs that we were then tackling in North Somerset. Until I could afford to purchase a Minolta Ring Flash.