BirdForum is the net's largest birding community dedicated to wild birds and birding, and is absolutely FREE!

Register for an account to take part in lively discussions in the forum, post your pictures in the gallery and more.

Reply to thread

Message: <blockquote data-quote="ronh" data-source="post: 1309560" data-attributes="member: 55514">Hi, Kevin,Thanks for all the observing and reporting, which was interesting. I don't know anything about the Monarch, unfortunately. I believe the effect is due, not to poor coatings, but to poorly cut roof edges. I guess the cause is sort of a moot point to any normal consumer, so I'll run my version of it by you for your entertainment and critical comment, if you don't mind.The streak of "dead space" along an imperfect roof edge is similar to the diagnonal mirror supports in a Newtonian reflecting telescope, which astronmers try to make as thin as possible, and take pains to align with the optical axis, to minimize such effects.  If the roof edge is sloppy and has cosiderable width, its diffraction pattern will be narrow, with the result that a lot of diffracted light will fall into the visible part of the image. As the streak gets narrower, less light is diffracted, and in addition its diffraction pattern gets wider, so the effect becomes less and less visible.If you have a good reason to think it's due to the coatings, please explain.Ron</blockquote>