Spoiler alert: this is a tease. The actual construction will be discussed in another posting. For now, I will give a quick illustration of why all the cool kids like to have "a fast prime lens" for their cameras.
Here is a local model in available light, f/1.8 handheld at 1/30 second exposure.
This shows up on my monitor exactly as I saw it at the breakfast table. With the zoom lens that came with the camera, the camera would have popped the flash and spoiled the natural light, or else the exposure time would have been so long the image would be blurred from either camera shake or childish motion.
The subject is so sharp you could cut yourself looking at the picture. The background is blurred almost to obscurity. To save you having to download a multi-megabyte file, here is a 100% crop:
The blobs of color are magnetic letters on the fridge. The effect on screen is very very like the effect of your (my) own pupils dilated to take advantage of low available light, focused on the subject with everything else unfocused. Next time you are out in the dark, notice how everything in front of and behind what you are looking at is out of focus. If you want to make an image that looks just perzactly like what you will see in your memory of an event, sometimes a fast prime lens is the way to get it done.
It doesn't focus to infinity and the aperture ring is off a little. But in its effective range, it is magic. Plus, it can give fanboys fits and make those with stacks of orphan FD mount lenses (or a bit of esoteric photography knowledge) wonder just what exactly is going on here . . .
. . . this is, after all, supposed to be impossible.
"You mean impassible. Nothing is impossible."