Optolong L-eNhance filter review

Every year, the illumination from cities is becoming stronger and stronger, creating difficult conditions for shooting deepsky objects. However, progress does not stand still – various filters have appeared that make it possible to cut off spurious light. Narrow-band filters that allow only a specific wavelength (hydrogen H-alpha, oxygen OIII, sulfur SII) have been used by astrophotographers for a very long time and make it possible to capture gas nebulae even under the conditions of strongest exposure. The hero of today’s review is the Optolong L-eNhance filter, passing only the H-alpha, OIII and H-beta lines. In combination with a color camera, it allows you to get a full-color image at once with one frame. Optolong L-eNhance will be of interest primarily to owners of color cameras and aperture telescopes. I immediately warn that it is not suitable for shooting objects of stellar nature (galaxies, star clusters, dust nebulae).

График пропускания фильтра Optolong L-eNhance, заявленный производителем

Filter bandwidth declared by the manufacturer

Packaging, appearance
The filter is delivered in a cardboard box. Inside it is a transparent plastic box for storage and transportation. Filter weight 5.4 g, thread diameter 28.5 mm, filter thickness with thread 7 mm, without thread 5 mm, light diameter at the inlet and outlet – 26 mm.
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Light pollution filters test

I have accumulated a sufficient number of different light pollution filters. I decided to conduct their comparative testing both with a spectroscope and in the illuminated city night sky. To take the spectra, we used an inexpensive  spectroscope with aliexpress, Canon 550Da camera (a blue filter was removed), an Industar 50-2 lens, and the Sun as a light source. The night test was carried out in the center of Anapa, and the illumination from the Moon also prevented. The results are below.

Spectrums of astronomical light pollution filters.

Spectrums of astronomical light pollution filters.

Night sky test:
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The problem of urban illumination is becoming more and more important every year – new houses, new roads, illumination, thoughtless design of urban lighting lead to the fact that the sky turns into a solid orange canvas, and because of the bright background it is impossible to capture even bright nebulae. The situation changed dramatically after the appearance of specialized light pollution suppressor filters for astrophotography. The use of interference coatings made it possible to cut off unnecessary regions of the spectrum — for example, the emission lines of mercury and sodium lamps, and to transmit the regions of interest — emission lines of hydrogen and oxygen.

There are several varieties of  light pollution filters — broadband and narrowband. In broadband filters include CLS (City Light Suppression), LPR (Light Pollution Reduction), UHC (Ultra High Contrast), UHC-S. They may be under different brands, but they have one task – to weaken the illumination of city. The UHC bandwidth is narrower in the green area, they are more suitable for heavily exposed areas, but it’s harder to get the corrent white balance. The usual bandwidth in the green region is from 20 to 75 nm. The narrower the filter, the darker the background is. Also, CLS \ UHC filters can pass the red region of the spectrum – this is not important for visual observation, but it is very important for photography, since the emission line of hydrogen nebulae (H-alpha) is in that area.

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