Bolex Product Code :- TUBEX 1st Type of Extension Tubes, 266.440 EXTUB 2nd Type of Extension Tubes.
By screwing an extension tube or a combination of extension tubes together and placing a lens on one end and screwing the other into the camera's lens mount you are able to use a lens to focus on objects far closer to it than you would normally be allowed to.
This enables you to make use of the current lenses you have to focus on subjects that are closer to the lens than normal. However the depth of field does decrease.
Extension Tubes are available in two sets, the first with the Bolex Product Code TUBEX contains four pieces of lens tubing in 5mm, 10mm, 20mm & 40mm lengths which can be used to make up extension tubes in 5mm steps up to 75mm.
The second set with the product code EXTUB contains four pieces of lens tubing in the lengths 3/8", 1/2", 1" & 2" and is much more rare than the TUBEX set.