Ideal etalon size

[moriniboy]

If you have carried out the PST stage 2 mod you will be aware of the restrictions caused by the small etalon aperture and associated sweet spot.

My question is what would be the ideal size for an etalon, has anyone got any info on the larger diameter Coronado / Lunt items.

I'm thinking for both visual and imaging based upon a BF15 and keeping an eye on overall etalon cost within sensible limits.

[Merlin]

The "ideal" size etalon would be the biggest you can afford. I don't mind the restricted view in the PST at higher mags - we get used to it.

I also have the front aperture LUNT LS50F and B600. At the moment, I'm double-stacking  the LS50F with the PST and it works fine.

As another forum member some time ago said, the ideal set-up is a front aperture etalon mounted on a good refractor.

[hunterknox]

Don't know about the most cost-effective solution but I'm guessing that internal reflections from foil-spaced etalons might be a pain to sort out. I know people have done it but forewarned is forearmed and all that.

I'm not sure about the Lunts but my 60mm Coronado is threaded at the front and rear, which could be useful for mounting purposes.

Good luck!

[Merlin66]

The best etalon is an external etalon, it then works directly in the f109 solar beam.

The Lunt 50 I believe has a 35mm internal etalon, the Lunt 60 a 30mm etalon. Not sure about the larger sizes....

The Coronado Solarmax 60 II, uses a very similar internal etalon to the PST (20mm).

[Peter Drew]

I've done direct comparisons between a 102mm Vixen flourite operating at 90mm aperture as a PST mod with a BF15 and a 90mm front etalon Coronado. Apart from the sweet spot of the PST mod there was very little difference. Well, apart from the price! 

[Merlin]

If, as you say Ken ( Merlin66 ), the LS50F has a 35mm etalon, this means that the PST's 40mm aperture doesn't vignette the LUNT's 50mm aperture.

This is good to know, as I thought that 10mm of the LUNT etalon was probably being vignetted.