Yes. You risk overheating the adhesive that bonds the glass components internally, unless you use a solar filter on the front (sun end) of one tube of the binoc

Yes. You risk overheating the adhesive that bonds the glass components internally, unless you use a solar filter on the front (sun end) of one tube of the binoculars, and complelely cap the other tube with its lens cap. My advice is to skip the binoculars. Instead use a simple magnifying glass like you can buy at an office supply store -- a round one, not a square one -- and a piece of poster board just like you did last time. It will work fine. The image will be upside down but who cares? If you can't get a magnifying glass, use a second piece of poster board and put a whole in the middle with a pin, or tack. The image on the other poster board will be very dim but almost as good.