L-PRO Filter Optolong Clip Canon EOS-R

Everything you need to know about the Optolong L-Pro filters

The Optolong L-Pro filter is a multiband anti-pollution filter. It is designed to increase the contrast of deep sky objects, whatever their nature. It selectively removes specific wavelengths of light pollution, whether artificial (mercury vapor lamps, high and low pressure sodium lamps) or natural (atmospheric chemiluminescence). In contrast, maximum transmission occurs at wavelengths of astronomical interest: OIII (forbidden lines of doubly ionized oxygen at 496 nm and 500 nm), H-beta and H-alpha (Balmer series lines at 486 nm and 656 nm, respectively), NII (ionized nitrogen at 654 nm and 658 nm), SII (ionized sulfur at 672 nm).

This graph shows the percentage transmission (ordinate) as a function of incident light wavelength (abscissa). The green vertical lines correspond to the characteristic wavelengths of the celestial objects (H-alpha, H-beta, OIII, etc.). The yellow lines are those of conventional light pollution (sodium vapor and mercury). The red curve is the transmission of the Optolong L-Pro filter.

Its characteristics make it particularly interesting for visual observation or photography in peri-urban environments subject to strong light pollution. A filter such as the L-Pro does not eliminate the effects of light pollution, just as it does not increase the brightness of celestial objects; it simply enhances the contrast between the objects and the darkened background of the sky.

The L-Pro filter removes ultraviolet and infrared light. Therefore, it can be used as an L-filter on CCD images. It has a wide transmission to ensure the best possible natural color balance. This balance greatly reduces unsightly color casts when photographing deep sky objects such as galaxies or star clusters.

Comparison between L-Pro and Clear Sky filters taken by Arnaud Besançon with a Canon 5D Mark III camera and a 24 mm Samyang lens (exposure time 13 s at 3600 iso, F/2). The 3 photos are raw images.

WARNING: The Optolong L-Pro filter is not designed for observing the Sun. Never observe the Sun with this type of filter; you risk serious and irreversible eye damage, including blindness.

This filter is for photographic use only. It is mounted in a special frame that fits in front of the sensor of Canon EOS-R cameras.