My PST etalon adapter has been sent to my friend for modification, after that, the PST-BF5 can be used with it other than a regular BF10.
Such configuration will:-
1. reduce the optical path length of the whole system
2. allow higher light transmission
3. allow straight through usage
(1) is a result of shorter PST-BF5, and thus, a Herschel Wedge might be used as an ERF (Herschel Wedge requires a lot of back focus). (2) also enable similar usage, for the Herschel Wedge cuts too much light when used with a BF10, which is far more opaque. (3) is great to make it more portable, why straight through is more portable? since I found it hard to use a 90 degree diagonal without a tripod, straight through will make it easier for pointing.
Let's see the result later!