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You can make your own camera lens for under $10! | Digital Camera World

Bit of cyanotype paper, an empty drinks can a pin and some black tape, you can make a *camera* for a few pennies.

True, any exposure less than 6 months might be disappointing... but it's still a camera

Definitely try this!

If you want a little more control over what you make, you can go onto Surplus Shed, use their lens finder, order an achromat and more or less pick your own focal length. For next to no money.

https://www.surplusshed.com/

Or you can buy similar achromats on eBay -- they are sold for DIY telescopes, e.g. https://www.ebay.co.uk/itm/175280761252

You're looking for a positive achromat (if it's negative the listing will say so, though), and it's probably worth buying one larger and "stopping it down" a bit so you're not shooting right to the edge, though a good achromat will be quite sharp centrally.

So far I have made three this way with Surplus Shed achromats (and one more from an old spare plastic meniscus lens from the Haynes "build your own camera" kit). My most recent shoot used several DIY lenses:

(More from that shoot on my profile but it's mostly NSFW)

Stopped down they can have a kind of glowy sharpness and really nice bokeh. 

Or the best one I've made produced this, wide open:

I have a cheap small 3D printer so I have gone a bit further than sticking them to bits of card.

But for focussing I am using off-the-shelf M42 focussing helicoids (at the moment, because my own DIY focussing mechanisms have their challenges). So you can just use a helicoid and some cheap extension tubes to get close to the focal length of the lens.

Using an achromat like this really will get you a lens that behaves a lot like the Lomography Daguerrotype Achromat for relatively little money, and it's trivial to do things like experiment with aperture shape and pattern. And you get to experiment with aperture placement, orientation of the lens etc.

The photo above from my shoot was shot with a multi-hole "sink-strainer" aperture that is a bit like the Imagon.

If you're using an SLR, you are probably going to be limited to lenses above about 45mm focal length. Take a 45mm lens and stick it to a lens cap, stop it down a fair bit to say f/11 and you should have a focus-free lens. Or get something that has a focal length of about 75-80mm, get a short focussing helicoid, adapter and a set of tubes, and you should be able to make quite a nice soft focus portrait lens.

If you want to get really clever you can even get adjustable apertures in M42 mount.

You can roughly calculate aperture by dividing the diameter of the hole into the focal length of the lens -- though this isn't actually how aperture is calculated, it's close enough when there's one element and the aperture is close to the lens.

This is all a lot easier with mirrorless; you have more choices of focal length and they are a lot easier to focus.

Edited by Unfocussed Mike