I often get asked about the surgical telescopes (loupes) that I use for model making. These are very expensive £1K+ professional 2.8x magnification lightweight flick up lenses with an attachable LED coaxial head light - the latter is invaluable. There are, however, much, much cheaper alternatives out there.
https://www.amazon.co.uk/2-5X420mm-Portable-Surgical-Binocular-Magnifying/dp/B07R58NCGD
Single lens alternatives may give the required magnification for an individual, but at often a reduced field of view and definitely an unergonomic working range.
I encourage the doctors who I teach to at least purchase these, but the challenge arises when they wear prescription lenses. There are clip-on versions available, but these are not very stable and position the lenses a little further from your eyes than ideal, so reducing field of view.
The following shows a set that I have adapted to an old pair of plastic-framed prescription glasses for one of my students.
The bridge of the loupes was adapted with a bur in my Proxxon handpiece to match the shape of the corresponding bridge of the glasses. Both are made from a very slippery plastic which does not glue easily, so some open weave tissue paper was melted into the plastic surface with a dry soldering iron to give a retentive surface for the epoxy resin to infiltrate. The bridge was actually turned upside down so that it would give the correct operating position on these glasses - towards the lower half of the lenses.
In this pair of glasses the plastic bridge is fairly slender and so I elected to use some 10BA bolts to mount the loupes. They are supplied with some fairly large self tapping plastic screws, but these would have overly weakened the surrounding plastic frame. The hole positions on the frames were marked using a fine white pen paint marker through the holes in the loupe bridge. The holes were drilled to a very tight clearance for 10BA using a 1.2mm TC drill turned by hand and then minimally countersunk on the rear with a round bur. The heads of the countersunk bolts were rounded off so that they would not rub against the glabella.
The 10BA nuts were accommodated within the screw head recess on the loupes bridge.
Once I was happy with everything being centrally positioned, then the whole assembly was fixed in position with 24hr epoxy resin. The nuts were encased in the resin and a good fillet of adhesive placed top and bottom of the loupes bridge to improve stability.
Careful setting up of the loupes is essential, with the individual holding and focussing on one thumb at the required working range (approx 420mm). The interocular distance is adjusted until the thumb doesn’t move left or right when each eye is closed, alternately: once the image is fused, then the central adjuster is tightened in position. The convergence angle of the telescopes is also adjusted to suit the working distance, with no eye strain.
I would suggest that 2.5x magnification is a good starting point, to give a good field of view and depth of focus: 3.5x may suit some people but with a trade off of in viewing volume. The cost is fairly moderate, so if you wanted higher magnification then, so long as you purchased from the same manufacturer, the two should be interchangeable on the modified loupes bridge.
I hope this helps someone, giving an affordable option for reasonable quality magnification.
Tim
