For this i have used normal “passe partout” cardboard.
First cut a spacer. The thickness of that spacer is needed to fill the space when the leather is wrapped on the inside of the cap.
Make sure you put some extra tape on it. Otherwise this spacer wil stick onto the actual lens cap. Cut 2 identical strips. The width depends on the space you have on the lens hood. But don’t make it wider than 2 cm otherwise it won’t come of smoothly. Cut the first one at the needed length and wrap it around the lens (on top of the spacer which is already on the lens. Make sure that the ends fit perfectly. Secure it with a tape. Then wrap the second strip around it and make sure it fits perfectly also.
After drying put some glue ( i have used simple white wood glue) on the strips and place the square underneath them. Use the weight of the lens to press these squares onto the strips which are taped around the lens. Leave it for about half an hour again. Make sure you wipe of the glue on the outside.
After a half an hour take of the cap, remove the glue which is left on the inside and shape it with a sharp knife. Use a sharp knife. Most accidents occur with knifes which are NOT sharp enough. Now you can see where the tape on the spacer is needed for...
Grind the edges until they are smooth ( i have used an electrical grinder for that, which works much faster)
Now cut a, larger than really needed, piece of leather and let it soak in normal water for about 30 minutes. I have tried it with dry leather but that only works with very small lens caps. When the leather is wet, it is much easier to shape it around the lens cap.
Make sure you get real thin leather. The best leather is sheep or goat leather.
Put the same white glue onto the lens cap.. Take your time. Stretch the leather nice and easy around the cap. Don’t hurry and don’t stretch it too fast, otherwise the leather will tear !!
To hold the leather. I have used a tie wrap which works much faster than anything else. Just leave it overnight. Don’t force it drying with a heater or so !! Be patient.
When the leather is dry, take of the tie wrap, take the cap of the lens ,and cut of the larger parts of the leather. Make sure there is enough leather left for the inside of the cap.
Now the most difficult part of making a cap starts. You will have to fold the leather to the inside, but the leather is actually wider than it should be. The easiest way to do this is putting on the cap without cutting the leather perfectly. Leave it for about one hour on the lens and after that you can see perfectly where it needs some extra cutting.Take your time, and do this step by step. For this part i have used normal contact glue
When everything is folded and glued you only have to cut the inlay of the cap. Cut it the same size as the actual lens shade. Glue this part into the lens cap. Start from the middle and work to the outside. You are able to stretch the leather if needed and let it fit perfectly.
For finishing just use some neutral shoe polish.
Using the right material it will take you no longer than about half an hour making a perfect cap.