Usually, dry conditions don't require the use of a eyepiece scope cap, unless they're really dusty and breezy. But wet ones do... and if you use a maximiser/scope enhancer, then you cant flip down a butler creek. Aerosol can caps do the perfect job. Varied in size, pick one slightly loose so as not to be air tight, just tight enough to grip. You might find you get a few spots flicked back in when you pull it off if it's too tight. Remember, they don't have to fit over, they can be poked inside as well.