How I made a push-on lens cap for an older collapsable lens. This will work great for just about any size and type of lens. The lens I made one for is a russian built Industar-10. Like other russian lens's made around the same period not that many lens caps were made for them and most of those have long since been misplaced or cast aside. Leica made quite a few in the same diameter, but their most popular lens's were a bit larger and the caps that can fit the plentiful russian lens's can be a bit pricy. So, this is a solution. They're easy to make and extremely cheap, so you don't have to worry about dropping it or setting it down and forgetting about it - no more retracing your steps for an hour searching for that shiny little cap with the word Leica on the front. While mine certainly does not look like much, that can be improved upon. One simple and effective way is to cover it with leatherette, the same stuff on camera bodies. Or just go crazy on the paint job, make something unique to you.

website where I took the idea from: http://jay.fedka.com/index_files/Page413.htm

- If you do have an older press on lens and you find that it's not fitting very tightly it's probablly just that the felt around the inside is worn down or damaged. Since that's all there is to hold the cap onto the lens, simply replace it and you should be fine.

Step 1: Materials

All you need is:

thin cardboard - the back of a spiral notebook works great

felt

brown wrapping paper

paint - black is standard

scissors

ruler - camera lens's come in metric, this instructable does too, so equip accordingly.

Step 2: Begin Construction

There are two ways to do this.
- the lens I made my cap for had a 36mm diameter

Type 1:

First use the lens to mark a circle on the cardboard and cut out the circle.
Then multiply the lens diameter (36mm in my case) by pi (3.14) and cut a strip of cardboard to this length. The width of this strip will be determined by preference and how much space the lens provides. In my case 5mm.
Glue the two peices together, this can be tricky but just use small dots of glue around the circle, wrap the strip around it and once it starts to set place it over the lens -be careful not to damage anything with the glue- and wrap a rubberband around it. Leave this for at least a couple hours.
Finally cut a strip of wrapping paper as wide as the cardboard plus another 5 or 6mm. The extra will be cut diagonally about every 10mm. Fold this down then apply a very generous amount of glue inside the cap and press the paper into place. Once the glue starts to set and it is firmly in place coat the other side of the paper in glue, kinda like paper-mache. For larger diameter lens's also apply paper in this manner across the middle of the lenscap.
Once this dries completely it should fit tightly over the lens. Paint the outside and call it good.

Type 2:

Mark and cut out a circle 4mm wider than your lens.
Again multiply the diameter of this circle by pi (3.14) and cut out a strip of the cardboard to this length and to the width prefered. Then cut another strip of cardboard 1mm thinner and 1mm shorter.
Just as before use small dots of glue to attach the longer strip of cardboard around the circle. Then, before that dries, glue the smaller strip to the inner side of the larger and so it just touches the bottom of the cirlce.
Allow this to dry in the same manner as before, using a rubber band to hold it on the lens - though now you'll need something to fill the space.
Next as in the type 1 instructions prepare the glue-soaked wrapping paper and attach around the inside of the lens cap. Allow this to dry overnight, preferablly using wax paper to protect the lens and then securing the cap to it as before, turning this all upside down so that the lens presses on the cap keeping everything in shape.
Once this is completely dry you can paint the inside of the lens.
Then cut felt and glue it inside the cap.
Finish by painting the outside of the cap.