Astronomik UHC Visual Deepsky Filter 1.25-Inch
Astronomik 1.25-Inch UHC Deepsky Filter for Visual Observations
Mounted filter in 1.25" cell (M28.5mm x 0.5mm)
The Astronomik UHC is THE filter for visual observing, although you'll see from the paragraph below (about Suitability) that it can also be used for astrophotography (IR should be blocked).
You will enjoy using your Astronomik UHC filter because you will see more stars and more details in deep-sky-objects compared to using filters from all other manufacturers.
The Astronomik UHC (Ultra High Contrast) filter allows the transmission of nearly 100% of the radiation from both O-III and the H beta lines. Though the second window for the H-alpha-line is not intended for visual observing, it is important, if the filter is used with an electronic device. All annoying, scattered light from other wavelength sources, including local artificial light pollution, is reliably filtered out. With this strong blocking of the sky background an unexpected wealth of detail becomes visible for gas nebulae and planetary nebulae.
Astronomik UHC filters’ astounding high light transmission brings better views of deep-sky-objects even to small telescopes! The high transmission of our optical glass filters means that enough light is available to allow successful visual observations with telescopes beginning at 2" (50mm) aperture. Our Astronomik filters are optimized for use with telescope focal length f / ratios of f/4 to f/15. Transmission losses and chromatic distortions, which arise with other filters, only occur with Astronomik filters when extremely bright aperture ratios of 1:2 and more come into play. Another major advantage of our Astronomik UHC filter is the high optical quality of the filter glass. When using Astronomik UHC filters you will quickly notice the same needle-sharp stars which you are familiar with from your astronomical instrument without any filter!
- Visual observation (dark skies): Very good, for telescopes of all apertures and high exit pupil
- Visual observation (urban skies): Very good, for telescopes from 100 mm aperture
- Film photography: Reasonable, but very long exposure time
- CCD photography: Good, when used with an additional IR-block-filter
- DSLR photography (astro modified): Very good, colour balance is near perfect
- DSLR photography (MC modified): Good, when used with an additional IR-block-filter
- DSLR photography (original): Good, colour balance shifted but contrast enhanced
- Webcam / Video (Planets): Unsuitable
- Webcam / Video (Deep Sky): Good, if light pollution is a big problem
- Transmission of nearly 100% of O-III and H-beta
- Transmission of 96% of H alpha
- Entire Blocking of annoying wavelengths
- Ideal All-round Deep Sky filter even for small telescopes
- Not sensitive to humidity or aging
- Excellent carrier material. The optical characteristics of your telescope are not altered by the filter in any way.
- 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
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 |