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The idea of using a film canister as a collimation cap is an old idea. It was recommended in the past mainly because film canisters were widely available. However, with this age of digital photography I am unsure if it is still a good idea to recommend it -- mainly because it is not as available as it used to be.
There is nothing special about a film canister. Just find any cylindrical bottle that is 1.25" in diameter and it will do the job. For example, here is the USA, Walgreen dispenses medication in plastic bottles that happened to be 1.25" in diameter. Look around your home. Maybe you will find 1.25" pastic cylindrical bottles.
Worse case, just draw bulls-eye circles on a piece of paper then poke a 2mm hole in the middle. Then cut it and tape it to the focuser. Make sure the hole is centered. Now you have one of the cheapest collimation cap equivalence.
Jason
Last edited by Jason D; 03-05-2015 at 05:39 PM.
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