Apodizing Screen / Mask

[John]

We had a short talk at my astro society on these masks or screens which are, or were, used to reduce diffraction in the central area of the field to aid sharpness and contrast when viewing double stars and planets. The downside is lots of odd diffraction in the outer half of the field but apparently you get used to ignoring that.

Does anyone on the forum have experience of making or using an apodizing screen / mask ?

Here is a link to a web article I found on this topic:

http://www.astronomyhints.com/apodize.html

I might have a shot at making one for my 12" dobsonian

 

 

Edited April 20, 2017 by John

[ronin]

Suspect you need something like this: http://mathworld.wolfram.com/ApodizationFunction.html

Played with them many, many, many years ago (how old is this universe?), trying to improve the resolution of assorted optics in the defence field, NIR and IR, still restricted. Louise might know what. Worked with a couple of people from Pilkington at the time who were trying them out. I got dragged in as I had worked on a "simple" form of super resolution by non-uniform optics at university. In the limit of the rings being zero they could almost be said to approximate an apodisation filter. I overheard someone mention "apodisation" and threw in a comment along the lines of "Are you trying to improve the resolving ability of the XXX optics then?". Mistake, as they then had found someone that had heard of them.

Would never occurred as the physics was different, non-uniform optics depended on destructive and constructive interferance. Which last I knew you did  not get from an apodisation filter, there is no real change in phase.

You can see from the page given that when I read of an "apodising" filter for improving an achro I sort of cringe.