What is the primary purpose of the Askar Ultra E2 OIII/SII filter?
The Askar Ultra E2 is a specialized dual-narrowband filter designed for color camera users who want to capture images in the Hubble Palette (SHO). It isolates the Oxygen-III (OIII) and Sulfur-II (SII) emission lines, allowing you to collect the "S" and "O" channels to complement your Hydrogen-alpha ("H") data.
How do I create an SHO image with the Askar Ultra E2 and a color camera?
You will need to capture two sets of images. First, use a filter that passes Hydrogen-alpha (like an L-eXtreme, L-eNhance, or a dedicated Hα filter) to get your "H" data. Second, use this Askar Ultra E2 filter to capture your "S" and "O" data simultaneously. In post-processing, you will split the channels from both images and combine them using a tool like PixInsight's ChannelCombination to assign Hα to Red, SII to Green, and OIII to Blue (or any variation you prefer).
Can I use the Askar Ultra E2 filter with a monochrome camera?
While it is designed for color cameras, you can use it with a monochrome camera. However, because it passes both OIII and SII light at the same time, you cannot separate the two signals onto the mono sensor. For monochrome imaging, using individual OIII and SII filters is the standard and more flexible approach.
Why does the Askar Ultra E2 filter have 3.7nm and 4.0nm bandpasses instead of just "3nm"?
The "3nm" is a class or series designation. The actual measured FWHM is 3.7nm ± 0.3nm for OIII and 4.0nm ± 0.3nm for SII. These precise, ultra-narrow bandpasses are what provide the exceptional contrast and light pollution rejection by isolating the specific nebula emission lines from background skyglow.
How would the Askar Ultra E2 filter perform on the Wizard Nebula (NGC 7380) from a city?
The Wizard Nebula (NGC 7380) is rich in all three SHO gasses. From a city, the Askar Ultra E2 filter's narrow 3.7nm/4.0nm bandpasses would be highly effective at cutting through light pollution to reveal the intricate structures in the OIII and SII regions. It would darken the sky background significantly, increasing the contrast and making the faint nebulosity visible in your exposures.
Will the Askar Ultra E2 filter work well with my fast f/4 telescope?
Ultra-narrowband filters like this one can experience some band-shifting with very fast optical systems (typically f/4 and below). While it will still provide a significant contrast boost, you may see a slight reduction in transmission compared to its peak 85% rating. The filter's performance is optimal for systems at f/4.5 and slower, but it remains a powerful tool for light pollution suppression even on faster scopes.
