VHT 2.00" – DGM Optics™ Nebula Astronomy Filter

SKU: VHT200

Description

The VHT (Very High Throughput) filter is an excellent Nebula filter for smaller scopes (4-6 inches aperture) where light gathering and throughput are at a premium.  It is also quite effective with larger scopes. The VHT filter offers a good compromise between an Ultra High Contrast type filter and a Broadband Light Pollution Reduction filter and has the quality of enhancing emission and reflective nebula with a minimum of background stars being dimmed. If you have ever viewed with nebula filters and felt “cheated” by the reduction of stars in the FOV then you will be pleasantly surprised by the VHT filter.

Spectral Curve

Measured spectral data for typical VHT filter

Specifications

This DGM Optics custom designed filter is well suited for a variety of telescopes and objects. The filter design stresses maximum optical throughput utilizing state-of-the-art optical thin-film designs and materials.

This filter is a “first surface” hard oxide thin-film and is much more durable and long lived than laminated “soft film” designs used by several famous makers. They are also much less prone to the internal reflectance problems that plague laminated filters.  Laminated filters can produce a very undesirable “doubling” of stellar images often with one of the doubles being red.  Contrary to popular belief, this image doubling is not due to the red sideband component that many nebula filter designs produce, but in many cases is due to laminated glass not being exactly parallel to the protective cover plate after lamination. Many laminated filters display this annoying characteristic.

This filter averages around 1% Transmission (optical density of 2) through the rejection region from 540 to 590nm, and average transmission greater than 90% Transmission in the passband, and greater than 75% at the 656.3nm H-Alpha line. The design yields a filter with a very symmetrical shape and high optical throughput, for maximum enhancement of nebula with a minimum of loss of stars in the field of view.

The substrate is B-270 and has measured total wavefront values of .5 waves. The combination of first surface optical thin-film technology and a polished, flat substrate enables this filter to be used with high magnification, a real plus for small planetary nebula.