Often we suggest to people to improvise a ground glass or focusing screen to check whether their camera / lens is focusing or imaging correctly. Solutions include using scotch tape or wax paper on a piece of clear plastic, scuffing the plastic to make a "ground" surface, actually making a ground glass with abrasive grit (grinding is easy but cutting the glass to size is a bit harder), etc.
Here is a common household item that has about the right combination of transparency and translucency to quickly improvise a focusing screen, and can be easily cut to any shape with scissors - an LDPE plastic lid from a coffee can (or other common food items).
The plastic is not rigid, so it's not flat enough to be used for critical focusing, but it will work for coarse "why can't I focus my lens" problems. If you wanted to get a little more accurate you could stiffen it with a frame of more rigid material. Here it's also a dust cover for the body.
Here is a common household item that has about the right combination of transparency and translucency to quickly improvise a focusing screen, and can be easily cut to any shape with scissors - an LDPE plastic lid from a coffee can (or other common food items).
The plastic is not rigid, so it's not flat enough to be used for critical focusing, but it will work for coarse "why can't I focus my lens" problems. If you wanted to get a little more accurate you could stiffen it with a frame of more rigid material. Here it's also a dust cover for the body.