Hi Joe, sky pollution filters are still made. Most every filter manufacturer has one available for sale. Narrowband filters address specific needs. A major...
Hi Joe, Yes, light pollution reduction filters are widely available and some work well for removing the type of light pollution which is created by many kinds...
Hi my NII filter workaround will have to wait. I just received the Custom Scientific 3nm Ha filter that I purchased on AstroMart. The filter looked physically...
Somehow I suspect that the problem may be with Custom Scientific quality control, rather than stability. Christian Buil also quotes a similar off-center...
Hi Samir, that's very interesting, thank you. I remember years ago that people were concerned about bandpass shifting in 10nm bandpass filters. Seems that...
Hi, after observing the out of spec Custom Scientific 3nm filter, I was concerned about my 2" Baader Ha filter. The last time I measured transmission of that...
Hi, I ran a few more Baader filters of mine through a precision spectrograph, +-0.06nm accurate. Four new 1000 data point files with filter curves have been ...
Richard: Tell us more about unstable filters ? I know that the V filter for measuring brightness for VSO degrades with time. I didn't think that dielectric...
Hi Larry, filter manufactures advertise their filter stability. Interference filters can be changed by moisture diffusion and temperature. See this for...
Hi, the Baader OIII imaging filter misses most of the 4959A line of OIII. The advertisements of the Baader Visual OIII filter touts capturing both the 4949A...
Hi, just to follow up on my 2" Baader Visual OIII testing, I measured the light leakage from 190 to 950nm. The chart can be seen in file folder Filter tests,...
Hi, I see a lot of HeII (4686A) in planetary nebula and I understand that HeII filters are used for finding Wolf-Rayet stars. Is there anybody here currently...
Hi Richard, very interesting! There's a lot of information on HeII in your images. Seems to be one of the last elements blown off the star. I'm going to get a...
I tried it on the crescent, and it has a Wolf Rayet star. I didn't see any action in the data but I may give it a half hour with high binning to try one more...
Hi Richard, one additional thought. What is the bandpass of your HeII filter? Gas maybe being expelled from the Wolf so fast that your narrow bandpass HeII...
Hi, I have tested the 1" Thorlabs 470nm 10nm (HeII) fitler. The chart can be seen in file folder Filter tests, file Thorlabs_HeII.xls. Notice that the filter...
two comments: these low cost filters are often designed for creating monochromatic light rather than for imaging. To be useful for imaging there is a substrate...
Hi Richard, while my skies are cloudy, I have been able to image terrestrial objects ~2+ miles away. Even with a 1% ND filter in series with the Thorlabs 470nm...
Hi, a week or so ago I was searching eBay for astronomy filters and saw a 37.5mm mounted Omega NIR 809nm filter that looked narrowband and only cost $37 + $5...
Hi Richard, I have been doing a little reading where gas being expelled from Wolf-Rayet stars can exceed ~4000 km/s. That could cause a spectral shift of...
mine has a 4.5nm stated bandpass I have used it with success on M57, M27, NGC7635 and M42 I plan to try with Thor's Helmet when it comes into position I had no...
Hi Richard, I noticed that AstroDon says he shifts his filters somewhat to the red to compensate for fast optical systems. He claims that other manufacturers...
I don't know how that works: not all of the light rays are angled.... Astrodon says lots of things including things that are mutually contradictory; depending...
Re: filters shifts to the red to compensate for fast optical systems ... If a NB filter has a flat top, the transmission profile is placed in a way that the...
Of course that is only an approximation; not all rays have the same angle on the filter. the on-axis rays are perpendicular the chief ray angle for a extreme...
Hi, I just couldn't resist the purchase of a $119 Omega 2" Hb filter sold on eBay. This filter is from a lot of 10, I purchased the first one, nine remain....
Hi, this filter will be returned for refund. I did an out-of-bandpass transmission test, 190-950nm. The file can be seen if file folder Filter tests, file...
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