ptolong Variable Polarizing Filter - 2”
Adjust the brightness level of the Moon, Venus, and other bright objects with the Optolong Variable Polarizer. A standard Moon Filter is similar to a pair of sunglasses. They work fine, but sometimes the scene is too dark or too bright, and there’s not a lot you can do about it. A variable polarizing filter is much more flexible than a Moon filter. It allows you to set the percentage of attenuation by turning the top section of the two-piece filter. Simply attach the 2” threaded filter to a like-sized eyepiece or astro accessory barrel, and then slowly rotate the top half of the filter—it turns 360°—to achieve the results you desire. Now you can apply more filtering to a full moon and less to a beautiful crescent—it’s your call!
The Optolong 2” Variable Polarizing Filter also works great to cut brightness when you are using your telescope for terrestrial observations or photography. If you have ever done photography through a SLR or DSLR camera, you may have already been introduced to the qualities of a polarizing filter, since it is a very popular accessory for polarizing the light and making the sky appear more blue. You will especially appreciate a polarizing filter when viewing over water or photographing a scene that includes a river or body of water. Simply turn the filter until you achieve the most glare-free results—you will really see the difference!
The Optolong 2” Variable Polarizing Filter is made with Schott glass that has been multi-coated with an ion-assisted deposition technology to ensure scratch resistance and stability on the central wavelength, or CWL. The filter cell is made of lightweight, strong metal and is CNC machined, sand-blasted, black anodized, and then laser engraved. The result is a super thin filter cell that will produce a clear aperture of 45mm.
Quality Filter Materials:
 
Schott B260 substrate material from Germany, 2.0mm thick
CNC machined and black anodized aero-metal filter cell that is ultra-thin to provide largest clear aperture; Laser-engraved to prevent fading
Multiple layers of anti-reflection non-cementing coatings applied via electron-beam gun evaporation with Ion-assisted deposition
 
Optolong Filter Manufacturing Processes and Parameters
 
Filter substrate is fine-optically polished to 1/4 wave and <30 parallelism over both surfaces
Surface quality, according to MIL-O-13830, is 60/40
95% transmission
High value transmission of pass-band and optical density of off-band is assured through Optolong’s planetary rotation system, a homogenous and precise coating procedure
Thin metal cells have a clear aperture of 45mm for 2” filters
Each filter comes with a plastic case with high pressure EVA case lining