It certainly will adjust my thoughts on the tube length Ken. I've decided to leave the design of the PST back end for later, I need to think about it more. However I've crunched some numbers, and played with sketchup for the first time tonight - a cool little program. Very useful for working out baffle placement and technical drawing in general. This is to scale.
http://i305.photobucket.com/albums/n...4.jpg~original
I've planned to segment the tube at the second baffle, for easier storage and transport. Each section will be about the same length if a dew shield (not shown) is factored in. At this stage, I'm focusing on night astronomy or solar viewing with a Herschel wedge. Due to the requirements of the placement of the etalon of a PST, I will most probably make another rear half with the etalon on there already, as the tube may need to be a different length to fit it in (and all the blocking filters are only 1 1/4", I've allowed for a 2" diagonal).
Any ideas or suggestions welcome.
Regards
David