Ordered lenses – they just arrived. Brilliant! Put them in a second prototype of the Camera Obscura .

See images below for with/without lens. Advantage: image can be seen much better with the naked eye. Disadvantage: image is circular and does not spread evenly over the square of the viewer.  Need to think about focal length as well …. 

On focal length: The first step is to measure the distance from the window to the wall.  Ours was 3.3 meters. The lens we will need would be a focal length of 3.3 meters but eye doctors don’t use focal length as a measurement, they use diopter.  The is simple to figure out by dividing 1 over the focal length.  This gave us .299 but these lenses are only made in .25 steps.  We rounded ours down to .25.  If you had the exact diopter for the room, the image would be sharper.  We went to the optometrist in town and when we explained what we were trying to do, they just gave us the lens.  Make sure you ask for a + or a converging lens. A – or diverging will not work for this.

https://www.instructables.com/Simple-bedroom-camera-obscura-for-under-5/