Lunt LS152 - doublestacking with PST etalon?

[Pablito]

Hi,

I am wondering if it is possible to make PST etalon work with my Lunt LS152 as a doublestack unit. Below is a photo showing what I can unscrew without damaging anything (thanks Lunt for modular scope )

I have to mention that I have to focus out the focuser and even move BF diagonal a little out from focuser to reach focus with eps so there is a lot free space to put PST etalon between Lunt etalon unit and blocking filter. Lathe work is not aproblem - my friend will make any adapters needed.

The other thing to mention is that I am going to sell my BF1200 and buy BF1800 (straight through version I suppose).

Any ideas?

Thanks!

Pawel

[Merlin66]

Pawel,

I've successfully done the double PST etalon stacking, and it should also work with the Lunt, BUT I found it next to impossible to tune correctly. It is VERY, VERY sensitive and in the end I gave up.

I have detailed sketches of the adaptor I used between the etalons if that helps.

I also show the tuning set-up for double stacking the etalons.

One thing comes to mind....what is the backfocus for the Lunt? In the PST it's 200mm, the same as the front barlow element, so just mounting the PST etalons together gave a collimated beam. If the backfocus is different for the Lunt, this will need to be compensated for in the spacing.

[Pablito]

Do you think that I can put PST etalon just straight in the front of BF filter after removing it's front tube (from etalon side)? PST etaon always needs 10cm back focus?

[Merlin66]

The built in barlow lens at the front of the PST etalon is -200mm focal length, and the positive lens at the rear is +200mm focal length. If this doesn't match the rear lens fitted to the Lunt etalon you'll have some problems. The system needs to present a collimated parallel beam to the PST etalon; the final focus will then be 200mm behind the PST etalon.

[Pablito]

You are right - 20cm not 10

It won't be easy but I think I'll try to do it soon.

Many thanks for initial info. I'll be back