PST with red color filter

[casstony]

The redesigned PST has a clear objective that allows all of the sunlight to pass into the telescope, whereas the original design had an opaque objective which I guess blocked most of the light at the objective.

With the aim of blocking much of the unnecessary wavelengths, today I tried a 2" red color filter in front of the objective. I had difficulty seeing a difference between the two images. Wondering if anyone else has tried this?

[sheeny]

Not with a 2" filter in front of the objective, but I have played with different colour 1 1/4" filters, and polaising filters on the EP.

I would not expect the red filter to have any effect since it should be transparent to red wavelengths, of which Ha is a very narrow band.

The best filters to try with the PST from my expoerience seem to be a polarising filter or a moon filter (or ND). The polarising filter is reported to give 20% (?:shrug: I think?) better contrast in some orientations. How you measure that I don't know. From my trials I think it made a small difference. The moon or ND filter I think just dims the image a bit but sometimes makes the image just that bit easier to look at, and not so long for the eye to adjust. I notice sometimes you look at the image for a while to see the detail, then move the eye a little bit and the detail disappears until the eye adjusts again... that effect is reduced with the moon filter.

As for the other colour filters... they look different but whether you can see any different detail, I don't know. In theory I don't think it should make any difference.

Al.

[casstony]

Hi Al, my aim with using the filter in front of the objective was to reduce internal heating and stess to pst components. I guess Coronado engineers think the design is ok, but it seems ideal not to have the full force of the sun coming through the objective. Just recently I singed my hand with a magnifying glass while showing the kids the power of the sun (meaning to burn through paper, not my hand). I figure if I can keep some heat out of the scope without degrading the image, why not do it.

[sheeny]

I suggest a neutral density filter in that case, but I suspect the Coronado engineers probably have a pretty good idea what they are doing, so I don't know if you'll achieve much. Give it a whirl though, there nothing to lose!

The PST is supposed to be designed to be thermally stable when viewing the sun. My observations are that if you look though it as soon as it points at the sun, the image is not as clear as after a few minutes when the scope reaches thermal equilibrium. That suggests to me the designer's knew what they were doing...:)

Al.

[casstony]

I'm sure the designers do know what they're doing, but I see the redesigned pst as a second best option designed to bypass the problems of the original objective. Alternatively, could be my paranoia, or maybe I just need to get out of the sun :-)