PST mod double stack

[spaceboy]

Just a thought, has anyone ever done a PST mod double stack or is this not possible ?? Can you not stack etalon in some way ? Sorry for my ignorance if this isn't possible.

[Moonshane]

I think Peter Drew tried but found it too fiddly to set up with poor reliability.  I suspect if you spent enough time and money and thought it might be possible but given PD's skill and experience I doubt it.

[Gazabone]

There is a commercially available one specifically for the PST;

https://www.tringastro.co.uk/coronado-solarmax-ii-40mm-double-stacking-etalon-with-richview-tuning-system-11116-p.asp?gclid=CMW1yaWNrtQCFSwq0wodR3oFwQ

 

but at £735, a bit pricey. You also need a converting ring to fit which I think is about another £40. 

[Mark at Beaufort]

I think the question is - 'is it possible to have a double stack etalon on a PST modification scope?'

I recently purchased a double stack unit from the classifieds - mine is a pre Meade unit and screws straight into the PST without the need of an adapter/converting ring. The surface detail is much better than the standard PST.

However, it will be interesting if someone has successfully done a double stack on a PST Mod - although I guess it will be very expensive.

 

[Moonshane]

I think the problem with this one is that it is designed for the front of the PST so requires parallel rays not converging rays as per after the objective as it would be in a PST mod (unless placed before the objective which defeats the object of the PST mod as your aperture is 40mm again).

[Moonshane]

Indeed Mark. You might be able to buy a used DS 90mm for the same sort of money.

[spaceboy]

I did think if it was possible, there would be at least some mention of it somewhere. With several searches of the WWW. nothing came up so figured it was a long shot but worth asking all the same just out of curiosity if nothing else.

[Peter Drew]

As "Moonshane" mentioned, I did give it a try on a PST mod but was disappointed with the results compared to a standard PST mod. I believe that  Merlin 66, who has more experience than me, also tried this with similar results. The PST double stack unit is so expensive relative to the stock PST because the DS unit is a full 40mm diameter whereas the one in the stock PST is 20mm diameter. Etalons get more expensive rapidly as the aperture increases.  

[Ibbo!]

if we every get a day of long sunshine while I am at home and have no other duties i will put the 60mm coronado on the front of my pst mod and see what happens

[Merlin66]

Yeah, trying double stack PST etalons is definitely a labour of love and demands some special patience skill and training....in the end I gave up....(I do still have the drawings of the required PST to PST etalon adaptor)

Double stacking, using an external SM60 etalon can give spectacular results.

I have and use this arrangement, the results are just as good, if not better to those I used to achieve with a double SM60 external pair.

If you lend me a SM90 external etalon, I'm more than prepared to test the system for you. ;-)

 

 

[Merlin]

First, please don't confuse me with Merlin66. Ken Harrison knows far more about the subject than I do. In fact, Ken has helped me with many a solar modding query.               I have a standard PST to which I attached a LUNT LS50F. Being double-stacked gives better views of surface features, especially with regard to flares.                                        I also have a Stage 1 mod, using a 70mm/f.10 refractor. This arrangement gets me closer to the proms. As far as I know, double-stacking doesn't enhance proms, so, in this respect, there probably wouldn't be any point in doubling up on etalons in the Stage 1-mod prom mode.