Astronomik ASL31 - UV IR Blocker, L Filter, 31 mm, round, for LRGB imaging

The Astronomik UV-IR Blocker lets the full range of sensitivity of the human eye (according to DIN 5031) pass and blocks all other parts of the spectrum in the UV and IR. It is the ideal choice as a luminance filter for any kind of digital photography.

Because of the perfect blocking of UV and IR, all optical problems in these parts of the spectrum are avoided.

The filter is optimized for systems with focal ratios between f/0.5 and f/50 (thus: almost all). The typical transmission is higher than 99%.

Main use:

The UV-IR Blocker gives you a perfect parfocal filter for the luminance channel. It is also great as a dust protection for your telescope and camera.

Way of working:

The UV-IR filter provides a defined air-glass-air transition that is homofocal to the other Astronomik filters without clipping the visible spectrum. It is also very effective against dust particles and suspended particles of all sizes, thus protecting sensitive surfaces of optical components such as CMOS and CCD chips.

Tip:

Alternative to IR or MC filter for electronic imaging in systems containing refractive optical elements.

Alternatives:

UV-IR filter: when shooting with high-quality, UV-sensitive CCD and CMOS cameras.

MC clear glass when only dust protection is needed.

If you take color pictures in light polluted places, you should think about using the CLS CCD filter for the luminance data instead!

Suitability:

Visual observation (dark skies): It depends, for dust protection only

Visual observation (urban skies): It depends, for dust protection only

Film photography: It depends, for dust protection only

CCD and CMOS photography: Very good, if used with optics which contain refracting elements

DSLR photography (original): It depends, for dust protection only

DSLR photography (astro modified): It depends, for dust protection only

DSLR photography (MC modified): Very good, if used with optics which contain refracting elements

Webcam / Video (Planets): Very good, if used with optics which contain refracting elements

Webcam / Video (Deep Sky): Very good, if used with optics which contain refracting elements

Technical Data:

transmission at 97-99%

extreme steep edges at approx. 380 nm and 680 nm

Parfocal with other Astronomik filters

Glass thickness: 1 mm

Completely resistant against high humidity, scratches and aging effects

Diffraction limited, the filter will not reduce the optical performance of your telescope!

Astronomik filters are delivered in a high-quality, long lasting, filter box

Note on the protective ring:

Astronomik delivers the round filters from 31 mm diameter with a protective ring at the edge. The corresponding declarations of the manufacturer are available for download as PDF.

Filter transmission curve:

The horizontal axis is the wavelength in nanometers (nm). 400 nm is deep blue, at 520 nm the human eye senses green and at 600 nm red. At 656 nm is the famous "H-Alpha" emission line of hydrogen.

The transmission in % is plotted on the vertical axis.

The red line shows the transmission of the filter.

Visual filters: The grey line in the background shows the relative sensitivity of the human eye at night. The maximum is at ~510 nm and drops to longer and shorter wavelengths. You can easily see, that you can´t see anything of the H-alpha line at night (even if you can during daylight!) The sensitivity at 656 nm is 0% at night!

Photographic filters: The grey line in the background shows the sensitivity of a typical astro camera sensor.

The most important artifical emission lines are shown in orange. The artifical light pollution is dominated by see mercury (Hg) and sodium (Na), which are used in nearly all streetlights.

The most important emission lines from nebulas are shown in green. The most important lines are from ionized hydrogen (H-alpha and H-beta), double ionized oyxgen ([O III]) and ionized sulfur ([S II]). The square brackets indicate that these lines are forbidden.