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NextGEN Filters

All of the NextGEN series reducers accept the standard 48mm filter thread commonly refered to as 2-inch filter size. The filters from Optec are of the highest photographic quality and are available with many different transmission characteristics to enhance contrast, reduce background illumination or block certain wavelengths. Since the Optec filters have threads on only one side, they cannot be stacked. Click on each filter's stock number to view its transmission curve.

17430 Violet Light Rejection - Blocks the UV and violet light shorter than 420nm. Most refractor optics including apochromatic telescopes are not well corrected in the short wavelengths. Add to this, the enhanced quantum efficiency of the newer CCDs in this part of the spectrum. Without this filter, the stellar profiles of hot blue stars become bloated and off-axis stars show a small comet like tail due to laterial chromatic aberration. The NextGEN 0.33X comes standard with this filter.
17431 #8 Pale Yellow - Does a better job blocking the violet and UV at the expense of some blue. Recommended for monchromatic use when the most energy flux is to be passed.
17432 Premium UV/Violet Block - Optec acquired a limited number of Schott glass filters made from GG-435 glass. Similar to #17431 but of higher optical quality. (limited supply)
17433 #21 Orange - Blocks blue completely and some green light. Passes light longer than 560 nm.
17435 #23A Light Red - Blocks blue and green light completely. Passes light longer than 600nm. This filter will block the sodium lines from low pressure sodium lights and effectively darkens the night sky from a variety of light sources including the moon. The H-alpha light from nebulae is passed completely. A good filter to use when the moon is up.
17436 #47B Blue - Before the availability of cheap and good dichroic filters, this filter was used for RGB imaging to pass the blue band. Low transmission in the blue and very transparent in the IR makes this filter useful mostly for special projects.
17437 #29 Deep Red - Passes light longer that 610 nm. This filter is a little more effective than the #23A in darkening the sky.
17438 #58 Light Green - Like the #47B, this filter was used for early RGB imaging. The low transmission in the green and some IR leak makes it a poor choice now for color work. However, it is an inexpensive way to get the sharpest image from most telescope systems. Working at the visual wavelength peak, most telescopes including the popular SCTs and reducers will give their best performance with this filter.
17266 Deep Sky - Blocks UV, violet and sodium light completely. The filter passes the important emission nebulae features with +90% transmission.