[chunky (Clinton Wood)]

Hi there Leon,
Sorry I didn't check the messages here yesterday.

But it is a really interesting point. I had only experience with pretty much on-the-objective , but I would have thought that no matter where the mask is, it would still generate parallel light patterns that would be focussed at the film plane regardless.

For my Newtonian, the primary mirror doesn't know where the mask is, and doesn't care, as long as it is sitting relatively square to the incoming light.

It would vary if the mask was INSIDE the objective, probably, but for instance you could incorporate the mask into the end cap of the scope, so that it would not have the possibility of touching the objective on a refractor.

I think I have two TAK refractors with the masks, and they have reported that they work well.

Regards
Clinton