Want to make a lens yourself?
You can see the finished product in the photo above beside the bulk of the standard kit lens!
It is truly fun and only takes a few minutes to build, (please) remember to vote for me in the contest!
Step 1: Finding the Lens / Equipment Needed
You need a lens to make a camera lens, and a way to attach it to the camera.
The lens can be from a magnifying glass or just about anything.
I've made both my lenses from old glass, you can buy cheap glass online that wouldn't be scratched.
Toilet paper roll / Kitchen towel roll (empty)
Attaching to the camera:
I use a telescope adapter to connect the lens, and can slide the lens front and back to focus.
Step 2: Measuring and Calculating Focal Distance
After finding the lens you need to measure the focal length.
You can do this by standing on the other side of a big room from a point of light, in my case sun shining through a window.
Next measure the distance between the centre of the lens and the image focused on a surface.
In my case it was around 120 mm.
Now you need the flange distance of your camera. This wikipedia article can help with that: https://en.wikipedia.org/wiki/Flange_focal_distance
For a Pentax mount it is around 45mm (45.46mm to be exact).
After finding the flange distance, subtract that from the lens focal length to find the distance to put the lens from the camera mount.
Step 3: Building the Lens
Now the lens needs to be built.
Make a tube (toilet roll, duct tape, ...) the length of the final distance calculated in the last step but if you are attaching it to an adapter make sure it fits and if the adapter lengthens the flange distance, take that into account.
Now attach the tube to the lens (duct tape).
Step 4: Finished and Example Photos
Slide the lens onto the adapter (or attach to camera).
Move the tube and lens forward and backward to focus.
Step 5: Taking It Further
You could make your lens better with many ideas, here is a lens I made previously with an interchangeable aperture.
As you can see I could have taken my time and made nicer apertures, but I didn't.
You could make a cardboard extension tube, lens cap, compound lens and anything you can think of!
Have fun making lenses.
PS Please vote for me in the photography tips and tricks contest!