The most costly parts of the OtterVIS spectrophotometer are the optics. Even simple spherical lenses, which eg. would be the obvious choice for collimation, easily cost 25$ per piece and achromats are 3x that.

However, the world is full of 50mm camera lenses, and they can often be had for as little as 5-10$ per piece. The modern (post-1970) standard  lens is an excellent performer and at infinity it easily covers the 29.1 mm long linear CCD.

I considered standard 50mm f/1.7-f/2 lenses from the big five camera makers: Canon, Minolta, Nikon, Olympus and Pentax.[1]

Eventually I got two very cheap Pentax SMC-M 50mm f/2, so the spectrograph’s dimensions revolve around that. If I get my hands on lenses from the other manufacturers later on I will post .scad files for those.

Two Pentax SMC-M 50mm f/2 stripped to the lens barrels.

[1] Obviously anything here of decent quality could do, but I narrowed the choice down to lenses from theses manufacturers as:

1. It should be easy to find the parts
2. Quality control shouldn’t be an issue