No worries, Joe. H-a filters must use an "energy rejection" pre-filter that acts much like a standard white-light mylar filter. It removes the intense heat and blinding light, broadband, before it enters the H-a filter. Many of you who have used older H-a filters have had to "tune" the filter in order to bring-out the prominences and other H-a details. What you actually did was center the filter's passband on the H-a line. Like tuning a radio, only with light instead of radio waves. You gotta be tuned-in to the right station to get the broadcast. You won't get harmful levels of sunlight if not passing the H-a line, you just won't see the details you're after. I realized as soon as I walked away from the keyboard on my last post that mirrors with differnt reflectivities didn't affect Rich & Jims test, since both filters were used on the same scope. Here's the real test for f-ratio sensitivity: Repeat the test using the same scope and filters just to verify the first run's results. Now, stop-down the same scope to f/10 or longer and repeat the test. The image will be dimmer because of the reduced aperture, but we are comparing the filters relative to each other at 2 f-ratios, not the view before and after stopping-down, so ignore it. If the filters still behave the same, then I'm afraid that the TeleVue isn't doing what it's supposed to do. The only other thing I can think of is if Jim actually got a narrowband LPR instead of an O-III, placed in the wrong cell. Narrowband LPR filters still pass the O-III lines, but have a bandpass of dozens of nm in that region, not a mere 11nm. Contrast will be much better with a true O-III filter on certain objects. If another TeleVue filter can be obtained for comparison, that might shed some light on the apparent discrepancy also. Chuck --- Joe Bauman <bau@desnews.com> wrote:
Chuck, Your point about h-Alpha filters' performance changing raises a concern: If you change what wavelength it passes, does it then become capable of passing light that can damage vision? Thanks, Joe
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