PST Conversion

Saturnine (Jeff) · #1 02-02-2017, 05:41 PM

Hi All
Has anyone out there done a PST conversion. About 9 months ago I had a chat to Alex Massey about doing the conversion, as he was also thinking along the same lines but many other things have gotten in the way until now and the project was put on hold.
Are there any pitfalls to watch out for or specific design problems and is the conversion actually worth it in an noticeable increase in performance. I have done a bit of online research and found several sites with the stories of there own PST conversions and from what they say I probably have answered my own questions but am after some more 1st hand info from more local and recent experiences.
The scope that I intend to use for the objective is an 102mm f 9 refractor that I made several years ago using an Jaegers objective from Surplus Shed, which performed very well but is not being used much any more as it has been superceded by other larger refractors.

Clear Skies

Jeff

Merlin66 (Ken) · #2 02-02-2017, 06:17 PM

Jeff,
Over the years I have done MANY successful Stage 1 and 2 Mods. I have a detailed PST Mod write up, just drop me an email address for a copy.
Ideally you need an f10 system; a100mm f9 will result in a 90mm f10 outcome.

Saturnine (Jeff) · #3 02-02-2017, 11:01 PM

Hi Ken
Thanks for your reply and offer will send my email address soon. I suppose I should divulge more details as to where I'm up to in the project.
I have removed the brass objective tube from the pst body and machined a threaded sleeve to screw into the front of the etalon, that will slide into the draw tube of the 102mm and have purchased an 90mm Baader D-ERF. this will result in the new scope being an f10 system as seems to be the desired F ratio recommended although that's not quite accurate.
Have yet to machine the D-ERF filter cell, which is about the last job before assembly of the "new" scope I guess. Mounting the filter in the cell will reduce the aperture to 86mm which means the F ratio will actually be 10.6. Is this still in an acceptable ratio for the etalon to work effectively.

Merlin66 (Ken) · #4 09-02-2017, 10:51 AM

Yeah,
f10-f11 is close to optimum for the PST etalon assembly.

Saturnine (Jeff) · #5 09-02-2017, 01:50 PM

Going by my measurements the F ratio should be 10.6 , so fits in the optimum range. Your pdf was most helpful and easy to understand and along with the other Stage 1 mod. postings that I've read does give me some confidence that I'm on the right track. Still have some machining to do.