If you plan on taking photos of the sun, especially during the eclipse of the sun, you don't want to look through the viewfinder to locate the sun and burn your eyes out. So you need a "solar finder". There are lots of these for telescopes, but this one fits in the hot shoe (where the flash goes) on your camera. The sun shines through a small hole in the front and makes a dot on the angled part. When the sun shines in the center of the circle, then the camera is pointed at the sun properly. You need to use a solar filter (not part of this print.. you can buy them from astronomy supply stores) on the front of the camera so you don't burn out your camera or worse, start a fire in it. Then you can try various exposure settings until you get a good photo. This is for use when the sun is not totally eclipsed. For totality, you would slip off the solar filter in front and hopefully you would have already pointed the camera in the proper direction. Only during totality, you can use the viewfinder.
Anyway, to make this, I printed using ABS with a 0.35mm nozzle, using 0.1mm layer thickness. After printing, cut out a piece of white 3x5 card to glue on the angled part. Then push a pin through the back of the angled part's hole to locate the correct point on the card and draw a circle there. You might want to test it first outside with the sun (before drawing the circle) in case you had any warping problems printing this thing. You might have to use a fingernail file or 1 to 3 layer folded 120 grit sandpaper to sand off any excess ABS if it doesn't quite fit your hot shoe (especially for the slots). Have fun taking solar photos with your camera!
4 layers on top and bottom. 3 perimeters on walls.