Terry Richardson, Senior Instructor of Astronomy & Physics at the College of Charleston designed a "Make Your Own Safe Solar Viewer". View the sunspots during the current sunspot cycle 25, for any upcoming solar eclipses, and beyond. This set includes our L14954 achromat (71.9mm diameter by 700mm focal length) and a Barlow lens with a focal length of -19mm. For the achromat: Place the crown (double convex) with its strongest curve against the negative side of the flint. Use a couple pieces of masking tape on the edges to keep them from tpuching hold them together. The crown side faces the sky. For best results use a 3 or 4 small pieces of masking tape at the edge between the two elements to separate them so they don’t touch.
Using an achromat instead of a single element lens you will get to see more of the sunspots and less blue fringe around the sun (chromatic aberration). If you make your SSV 48” long you’ll get an 8” image. The larger diameter of this objectives lets more light in. With 53” long you’ll get a 10” image.
Here are the college's links for instructions and additional information: https://richardsont.people.cofc.edu/safe_solar_folder/large_image_SSV.html
