American Educational Unmounted Double Convex Lenses with Ground Edges, 50mm Diameter, 20cm Focal Length (Bundle of 5)

These were great lenses to be used for a STEM telescope project. We are using this inexpensive lens as part of a STEM project that school children will assemble and take home. This year we are focusing on an optics theme. This 50 mm diameter lens with a 20 cm focal length is the primary object in a Kepler-type telescope. The eyepiece uses a 38 mm diameter lens from the same company with a focal length of 5 cm that gives this PVC telescope a magnification of 4X. The body of the telescope uses two pieces of PVC, a 5.5 inch length of 2 inch diameter and a 5.5 inch length of 1.5 inch diameter PVC pipe. The ID of the 2 inch pipe and the OD of the 1.5 inch pipe were rounded with a router to ease assembly. Some small pieces of felt weather stripping were adhered at 120 degree spacing with double-sided VHB tape from 3M to center the pipes and provide smooth sliding friction. The lens holders are PVC trap adapters from Nibco. The 50 mm lens is held by a 2 inch slip pipe to 2 inch female PVC fitting (UPC 39923214201) and the 38 mm lens is held with a 1 1/4 inch slip pipe to 1 1/2 inch female PVC fitting (UPC 39923214188). The 50 mm lens needs a 7 inch length of nylon grommet edging (PN MGS-3-01 or similar) to keep it in the holder otherwise it passes right through. Some narrow adhesive foam weather-stripping can be used as well. You will need to use a sharp knife to remove part of the inner ring on the 1 1/4 to 1 1/2 adapter so the sealing ring will thread onto the adapter with the lens. Slide the two pieces of pipe to focus the image and the best image is seen with the eyepiece about 2 to 3 inches away from the eye. Total material costs are just under $9 each. Unfortunately, as of the time of this posting, the price on these lenses have almost doubled from the price I paid initially.

So angry. They sent me the wrong lens. I am not sure if it was the larger 50mm lens or the 38mm lens--but I bought packages of convex and concave--which when placed appropriately should have created a clear view. Only SOME of my students could get their telescopes to work correctly. We tried everything. It finally dawned on me that the lens must have not been correct (one convex and one concave). So infuriating and very expensive--summer program, very intense, no time to deal with it.

Great lenses at a low price!