EISCO Double Concave Lens, 500mm Focal Length, 3" (75mm) Diameter - Spherical, Optically Worked Glass Lens - Ground Edges, Polished - Great for Physics Classrooms

Once again, my first EISCO lens being a 75mm 20cm FL double concave that I was very pleased with, EISCO has again provided me with a pair of quality lenses, nicely polished and in excellent condition. On one, there was a very small chip on the outer edge that will have absolutely no impact upon my use as a precision top spinning stage, and I doubt it would affect optical usage needs either. The same was true of my first lens...it had one very small chip. One or two such chips, I would take to be normal for polishing glass, but if there were more and if the lenses received were consistently that way, then I'd fault EISCO and rate them less favorably. But for me, the two lenses like this that I received had one with the minor chip and the other was pristine. For the price I am very pleased with EISCO lens quality and recommend them.Note, the 50cm focal length is considerably thinner than a 20cm focal length. For reference, thickness is about 4mm for the 75mm/50cm FL lens versus 12mm for the 75mm/20cm FL lens, both being of the double concave type. Hopefully the thinner 50cm FL lens will remain durable enough for use as a spinning stage, but it could prove out to be too thin at the center, which I am estimating at 2mm thick. Still worth a try though.

Used this as a spin base for my tops. The glass is thinner than normal spinning bases but the depth is very much ideal as it is not too deep like the 200mm models. This keeps the top spinning much longer. I don’t recommend doing a drop spin on this but normal spins should be ok. Workmanship was nice and smooth compared with another brand I won’t mention.Overall am very happy with my purchase

I bought this lens to use as a reducing glass for quilt designing. I like the size - it's a bit larger than those sold as quilting specialty items - however, the clarity was less than I anticipated and the lack of a handle causes it to need frequent cleanings. Not ideal for quilting - I'll find another use, maybe give it to my grandkids for exploring.

Good

Meh.

Using this as a spin base for my tops, works great.

This is the perfect size for a spinning top platform.

I use these for spining precision tops. Works perfectly.