I recently got the chance to compare a local club's PST with my Lunt 50, with the PST being on a photo tripod, side by side with my LS50 on my CG5, at about the same magnifications (Solar disc size) in both scopes, and I studied the surface detail and proms and tuning and sweet spot of both instruments. I studied these all extensively over 2 hours and found that this particular PST has a serious problem with the image brightness (light transmission).
To give you an idea, the first eyepiece I put in was an 8mm which is a decent one to use for Sol in the LS50, but in the PST it was so dim I couldn't work out where focus was and I had to go all the way down to a 32mm Plossl until I could focus the PST properly and precisely. In fact, I found out that my LS50 is still brighter than the PST, at the same sized Sun disc, when the LS50 has a 13 PER CENT TRANSMISSION ND FILTER in the eyepiece!
I quickly came to the conclusion that this PST is badly / fully rusted over and the ITF filter needs replacing.
It didn't seem to affect the contrast, as it were, (which I thought was odd), since the PST had similar contrast on the surface orange peel texture on the Sun's disc, and the filaments were also similar in contrast compared to the Lunt, just that the visual image was about 1/10 the brightness of my LS50.
Edited by Live_Steam_Mad, 07 April 2018 - 08:14 PM.