Hi Les,
There is a difference, the SM40 is definitely better, but not by much. The main problems I've seen with the PST is that it's hard to get all of the solar disk in focus at once. The SM40 is much better in that regard. Other than that and a few design differences, they are both 40mm about 0.7A Solar scopes, so the views are similar.
Less bandpass (lower A) gives more contrast, hence more detail. There is a tradeoff though, as you lower the bandpass, you get less light through, so dimmer picture. What you want is a scope with <0.5A bandpass for surface effects (sunspots etc), but one with a wider bandpass for flares and prominences. That's why doublestacking can work very well.
Cheers
Stuart (about to go and look for a possible sunspot forming)
|