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These Generation 2 filters should be parfocal for systems as fast as f/3.5, if your optical system is well color-corrected. This LRGB (Luminance, Red, Green, Blue) filter set has a reduced UV contribution in its luminance and blue filters. This reduces star bloat in systems that are not well color-corrected. This makes these LRGB filters best suited for imaging with refractors and camera lenses, which often are not particularly well-corrected in the violet end of the spectrum.

On the other hand, the clear (no near-IR blocking) filter in Astrodon CRGB (Clear, Red, Green, Blue) filter set #TB2CI27R may produce bloated stars if your optical system has poor near-IR focus, as is the case with many camera lenses. For this reason, this near-IR blocked LRGB filter set would be the best choice for refractor and camera lens imaging, while Astrodon CRGB filter set #TB2CI27R would be better for imaging with reflectors, which are intrinsically more accurately color-corrected.

A narrow spectral “gap” between approximately 565nm and 600nm minimizes the effect of mercury and high and low pressure sodium city light pollution, as well as an airglow emission line due to ionized nitrogen in our atmosphere. This gap can be seen in the response curves in the feature image below.

This Astrodon I-Series 1.25” mounted LRGB filter set threads into any color filter wheel that accepts standard 1.25” threaded filters. Each is parfocal with Astrodon's high-performance narrowband (H-alpha, Oxygen III, etc.) and near-IR filters. The filters come in a hard plastic snap-lid storage case.

For more detailed information on Astrodon filters, click on the “Astrodon Generation 2 Filters” icon above.