Dealing with reflection between lens and filter?

[Mark Woods]

If you're getting kick back flares, images, etc., from the lens, put the filter at an angle to the kick doesn't go right back into the lens and over the image. I've done that also. Those solutions don't really have that capability.

[vinny]

So assuming that the light is coming from overhead, what's wrong with just rotating the opening to the horizontal position to cancel most of that problem?!

nothing, unless you're using a grad filter or if shooting a side-lit scene where there are clouds overhead. Avoiding extraneous light is a good thing

[Mark Woods]

By solutions, I meant the matte boxes.

[Struan Gray]

still looks like there's nothing keeping light from striking the back side of the filter though.

Sure. I just like the idea of elastic on the back and a drawcord on the front. Extending the idea to cover the whole shebang is left as an exercise for the reader :-)

If you're getting kick back flares, images, etc., from the lens, put the filter at an angle to the kick doesn't go right back into the lens and over the image. I've done that also. Those solutions don't really have that capability.

This often done with filters in laboratory optics setups. They tend to be flat to a fraction of a wavelength, and if you mount them parallel you can get some disturbing multiple reflections and/or interference effects.