Issue with double stack PST

[jeffwjz]

I have had an opportunity to own a double stack PST. I took the scope out with a 12.5mm eyepiece, and without the double stack module I'm able to get a reasonable view of the whole disk with some prominence. I then threaded on the double stack module at the front of the scope, immediately in the eyepiece the solar disk becomes very very dim and I'm having troubles to view the sun clearly, let alone distinguishing the surface details.

I understand the double stack module reduced bandwidth but I'm not sure if the image is supposed to be dimmed by so much that it affected the viewing. Is it something normal, or maybe some parts of my set up was faulty?

[Highburymark]

Doesn’t sound right. While double stacking slightly dims views, it should significantly improve detail. I haven’t owned a PST, so am not familiar with how you attach the DS filter, but it sounds as if you may have a problem - possibly even a decontacted DS etalon. Hopefully someone with more knowledge of PSTs might help.

[Peter Drew]

Narrowing the band width does reduce the brightness which is one of the reasons why imagers prefer the system as the enhanced surface details can be brightened by exposure and processing.  Visually, double stacking dimness can be offset by placing an opaque covering over your head.  If the PST is preowned it will be worth checking the ITF, the filter just before the blocking filter as theses deteriorate over time and also reduce the brightness of the image.  Finally, using a Ha telescope and more so a double stacked version is quite a steep learning curve with many nuances to deal with.  The usual advice is to tune the single stack to provide the best view and then to tune the double stack unit until the brightness is best.  Further refinement can be made by "clocking", rotating the double stack unit relative to the rest of the telescope.      🙂

[jeffwjz]

Thanks a lot I dissembled the eyepiece barrel bit and indeed the ITF is rusty, which could be the reason. I'll look to buy a replacement filter then..