Astronomik UHC-E Visual Deepsky Filter 1.25-Inch

Astronomik 1.25-Inch UHC-E Deepsky Filter for Visual Observations
Mounted filter in 1.25" cell (M28.5mm x 0.5mm)

The Astronomik UHC-E filter is our budget filter for deep-sky observation of emission nebulae and comets under light polluted skies. It’s particularly suitable for small ’scopes.

The UHC-E Filter increases contrast of emission nebulae and comets and blocks the light of typical streetlights as well as airglow. It is best suited for telescopes up to 5" / 125mm.

Main use

The Astronomik UHC-E filter provides a FWHM of 45nm and blocks the light of typical streetlights (e.g. sodium and mercury vapour) as well as airglow. Thus it increases contrast between your target and the night sky. The contrast enhancement is less than that of the Astronomik UHC filter, but at the same time the transmitted amount of starlight is greater. It's therefore better suited to smaller telescopes. As the UHC-E filter passes a spectral line of Carbon (due to the higher FWHM) it opens up the possibility of comet observation.

Other uses

• Observation of Jupiter’s clouds.
• Easier resolution of Double Stars.
• Photography under light-polluted skies with DSLRs and other cameras.

Alternatives

If you use a telescope with an aperture larger than 5", we suggest the use of our standard UHC-filter because of its greater contrast enhancement capabilities. If you use a telescope larger than 8", you can try our OIII filter for even better results when observing specific nebulae.

Suitability

• Visual observation (dark skies): Reasonable, an UHC filter is more suitable
• Visual observation (urban skies): Good, for telescopes up to 125 mm aperture and medium exit pupil
• Film photography: Good, but very long exposure times
• CCD photography: Good, when used with an additional IR-block-filter
• DSLR photography (original): Good, colour balance is near perfect
• DSLR photography (astro modified): Good, colour balance is near perfect
• DSLR photography (MC modified): Good, when used with an additional IR-block-filter
• Webcam / Video (Planets): Unsuitable
• Webcam / Video (Deep Sky): Very good, if light pollution is a big problem

Technical Data

• typ. 94% transmission at 486nm (H-beta)
• typ. 95% transmission at 496nm (OIII)
• typ. 95% transmission at 501nm (OIII)
• typ. 94% transmission at 656nm (H alpha)
• transmission 465nm to 530nm and above 645nm 
• Full width at half maximum 45nm
• Parfocal with other Astronomik filters
• Glass thickness: 1mm
• 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
• Since 2008 we do ship filters with a completely new design. Any kind of halo or strange reflection is a matter of past

How to read the above chart?

    * The horizontal axis is the Wavelength in Nanometers (nm). 400nm is deep blue, at 520nm the human eye senses green and at 600nm red. At 656nm 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 ~510nm 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 656nm is 0% at night!
    * Photographic filters: The grey line in the background shows the sensitivity of a typical CCD sensor.
    * The most important emission lines from nebulas are shown in green. The most important lines are from ionized Hydrogen (H-alpha and H-beta) and double ionized oyxgen (OIII) .
    * 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 major emission lines of artifical light pollution: | Hg 435,8nm | Hg 546,1nm | Hg 577,0nm | | Hg 578,1nm | Na 589,0nm | Na 589,6nm | | Na 615,4nm | Na 616,1nm |

The major emission lines of nebulas: | H-β 486,1nm | OIII 495,9nm | OIII 500,7nm | | H-α 656,3nm |