LUNT/PST double-stack.

[Merlin]

Is it possible to marry a Lunt 50mm front-aperture etalon to a PST as a double-stack?

[umadog]

Why do such a thing? The 50 mm Lunt unit costs $1,700. That's about 3 times the price of a PST (which start at $600). The PST double-stack unit is in the $600 region.

[Merlin66]

Certainly in theory it should work.

No real difference to using a SM40 up front.....

[Merlin]

Thanks Chaps. I have a LUNT 50mm etalon and a PST. Although cheaper, the PST seems to be able to take more magnification.

Even the wider field-of-view in the LUNT isn't a particular advantage. I find that the focus changes across the field, which is a bit of a bind having to keep refocusing. Is there a type of eyepiece I can use that might obviate the need to refocus?

In this respect, the area of sharp focus isn't any bigger than in the PST.

[Merlin66]

Hmmm

Can't help with the focus on the Lunt - I've never used one.

It would be interesting however to see the DS results with the PST......

[umadog]

Sorry, didn't realise you already had one.

The double-stacked PST is substantially nicer, to be sure.

In what situation is focus changing across the field? Is the Lunt etalon mounted onto a regular refractor or do you have a Lunt solar scope too? If so, does it look ok on other targets without the filter in place? It sounds like the focal plane is curved (http://starizona.com/acb/basics/optics/ccd_curvature.jpg) and if that's the case no eyepiece will fix it. It's weird if the etalon is doing that. Perhaps contact Lunt and ask?