1) should make a 1.25" interface for it, so that I can use it with my Herschel Wedge
2) measure the focal length and optical characteristics of the afocal lens system, see if one can be made for SM40
3) a 2nd hand Borg 125ED would be the ultimate tool if the Herschel Wedge idea works, by then even the C5 can be sold for the 125ED is both light enough and large enough, should be better than using the Cheapy-ERF both in terms of safety and elegance... I found an old 2nd hand one cost 10K HKD, which is very nice indeed... but that depends on luck!
4) shall also made a 1.25" interface for the BF5 of the PST, to fully utilize them
5) so three parts to make:  1.25" interface for PST etalon  1.25" visual back for PST etalon  1.25" interface for PST BF5... also to consider how to make a cell for Cheapy-ERF