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1) Is the filter able to block the led lights only in photography or also in visual? From what I knew there are no filters capable of blocking the LED lights in view.
2) what is the difference between this and the uhc-s filter?
2) what is the difference between this and the uhc-s filter?
Question by: Federico on Jul 8, 2023 2:53:00 PM | 1 Answer(s)
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Baader UHC-L DeepSky Filter
Planeoptically polished
All Baader UHC-L DeepSky Filter
1¼", 31mm, 36mm, 2", 50.4 mm, 50x50 mm, 65x65mmBaader UHC-L Nebula filter with highest transmission, realistic star colors, also usable as highly effective LED-optimized luminance filter for LRGB imaging.
The Baader UHC-L filter is the classic allround "light pollution rejection filter", but now also blocked against the main LED emissions in the blue part of the spectrum. The passband curve corresponds to a wide dual-band filter without distorting star colors. The two passbands transmitt all light emitted by the known gas nebulae (the H-alpha and H-beta lines of fluorescent hydrogen as well as the OIII line of oxygen), while both the atmospheric most disturbing stray light from LED lamps and intense bluish car headlights as well as further stray light from classical street lamps and the natural night sky glow (airglow/skyglow) of the atmosphere are blocked to a large extent. At the same time, the UHC-L filter is coated with latest technology (CMOS-optimized) and therefore blocks false light much more effective than all previous UHC filters.
Use of the UHC-L filter
The application of the UHC-L happens mainly in visual and photographic observation of emission nebulae (star forming regions, planetary nebulae, supernova remnants) under medium to highly polluted skies. Its use is also interesting for comet observation: It passes the OIII line at 501nm as well as the two C2 lines at 511nm and 514nm which are characteristic for the gas tail of many comets.
This UHC-L filter is the successor of the well-proven plane-optical polished Baader UHC-S filter. It consequently complements it with the advantages of CMOS optimization (no disturbing halos, blackened filter edges, Life-Coat™-coating) while providing an improved transmission spectrum adapted to also cover modern LED light pollution. It provides a brighter image than many classic LPR (Light Pollution Rejection) filters and is therefore not only suitable for large, fast instruments, but also for smaller telescopes collecting less light, where a large exit pupil cannot be achieved. This applies for long-focal length telescopes as well as for small aperture telescopes that only have an eyepiece socket for 1.25" eyepieces. Unlike the single line or dual.line narrowband filters, the image is also bright enough for high magnification, while not diminishing the number of stars. For deep-sky observers, therefore, this UHC-L filter is the perfect visual complement to narrowband OIII filters.
The UHC-L filter is also excellent for photographic use. It does not just block polluting terrestrial light sources, but at the same time it serves as a luminance filter (L-filter), since it blocks all UV and IR transmission like a UV/IR cut filter. An additional UV/IR-cut filter is therefore not necessary: Cameras without a built-in UV/IR-cut filter thus deliver significantly sharper images on refracting telescopes. Both classical photographers and users of EAA/LiveStacking do benefit from the increased sharpness of stars and better contrast of nebulae, as well as the improved transmittance in H-alpha.
Like all Baader CMOS-optimized filters, Baader UHC-L filters likewise are plano-optically polished, with ultra-hard, sputtered dielectric coatings. Even a one-hour bath in boiling water cannot harm these filters! They are scratch-resistant and can be cleaned as often as desired.
The Baader UHC-L / Ultra-L-Booster Filter offers all the advantages of the CMOS-opitmized Baader filters:
- Increased contrast, matched for typical CMOS quantum efficiency and s/n ratio
- Reflex-Blocker™ coatings, for largest ever freedom from halos, even under most adverse conditions concerning aux-optics
- Identical filter thickness to existing standards, with utmost care for parfocality
- Blackened edges all around, with filter-lead-side-indicator in the form of a black frontside outer rim, to additionally eliminate any reflection due to light falling onto the edge of a filter
- Each filter coated individually, with sealed coating edge (NOT cut out of a larger plate with coatings left exposed, read more)
- Life-Coat™: evermore hard coatings to enable a non-aging coating for life – even in a most adverse environment
Baader Blogpost:
New CMOS-optimized Baader FiltersThis entry was posted on May 8, 2021 Last modified on February 28, 2024.
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HALOS – viewed without prejudice
About Baader Filters
The variety of uses for filters in amateur astronomy has considerably increased during the last decade, enabled by both more accurately manufactured optical accessories, and, above all, by the “digital revolution“.
In the old days, colour filters for visual planetary observations were not screwed in the front part of the eyepiece, but were simply placed between the eyepiece and the eye. Plane-parallelism of these filter glasses was not important, because they were not in the optical path of the telescope.
Today, filters are placed in the optical path of the telescope, even well in front of the focal plane. This definitely requires some degree of plane parallelism and accurate production of the filter glasses.
Baader filter boxes can be attached laterally and above the other to create a sturdy unit. Each filter is then neatly in it's own drawer and characterised from the front with name, number and size of filter.
Every single cell mounted filter delivered to our customers is cut as a round or square disc in the according size (1¼", 31mm, 36mm, 2", 50,4mm, 50x50mm, 65x65mm), and then is polished plane to a quarter wavelength on both sides on a computer numerically controlled polisher. After that, the polished blanks are submitted to the costly coating procedures. This sequence is also used for all unmounted filters.
We deliberately avoid cutting filters from larger sheets, because the coating layers can be damaged at the edges and suffer from microscopic fissures. That lets moisture penetrate and the filters are subject to “ageing”. In particular, this applies to many of the complex dielectric coatings needed for nebular filters, UV/IR blocking filters and emission line filters. Damage to multi-layered filters at the edge results in greater damage than to a single anti-reflection coating. As our filters are not cut-outs, every individual filter disc can then be coated, but not right to the edges. This seals the filter, and no moisture can penetrate into the coating layers. Hence, even the most expensive narrow-band filters are free from ageing, and can be carefully cleaned without hesitation and as often as necessary.
Our UV/IR blocking filters were exposed for 1 hour to boiling water at the company B+W (Schneider Kreuznach, Germany). This accelerated ageing test corresponds to approximately 5 years of filter ageing in actual use. In contrast to cut filters, our edge-sealed filters showed no ageing and above all no changes to the measured transmission at different wavelengths.
The commercial disadvantage of this technology lies in the fact that we cannot produce any filter size by simply cutting it from a sheet. For custom-made filters in a requested size we need a minimum production run of 250 pieces.
High quality optical filters are not cheap. Hence, it is also no surprise if observers complain about „unaccountable“ picture deterioration when using cheap filters in front of binoculars, tele-compressors or Barlow lenses, either visually or photographically. The higher the magnification, the softer and more blurred the picture appears when using a cheap filter, for both visual and photographic observations.
In the manufacturing process great emphasis is placed on guaranteeing that a Baader filter must be bought only once by the customer, because it will be optimally usable for all use kinds of astronomical observations now AND in the future.
Interferogramm of a Filter from an overseas supplier
A stack of coating layers (up to 60 layers depending on the filter complexity) has a considerable thickness and, above all, a different coefficient of expansion than the carrier glass. When this stack of layers is cut at the edges, the entire stack of layers may separate from the carrier glass over time. Baader Planetarium, on the other hand, allows the coating to gradually run out towards the edge. This means that the outermost filter edge (0.5 mm) cannot be used for filtering, but the coating remains sealed permanently.
Ever since we began producing our own filters and series of filters, we have checked the quality of a wide cross-section of „cheap filters“ from different manufacturers (see picture on the right). Many filter manufacturers - mainly in Asia – apparently still take the view that a filter is used only close to the focal plane, and that, hence, a homogeneous glass substrate is not necessary and that it need not be polished fine optically.
They say that if only one cosmetically flawless, smooth glass surface is required, it is not necessary to achieve a high degree of plane-parallel polish. They further believe it is adequate to cut filters from a big stained glass sheet – usually in the format 20x20 cm – and to so-called “raw polish” the filter on both sides. With this process, the glass surface is slightly molten and all saw scratches and surface inaccuracies are invisibly levelled. But so-called „raw-polished“ glass surfaces are completely irregular and deform the wave front of the light significantly!
The “polished“ sheet is coated as the whole, and afterwards the filters are cut out in the desired size. This production method for filters is drastically less expensive than the substantially more sophisticated manufacturing of a Baader filter. In addition, different sized filters can be cut on demand, reducing inventory costs.
Such a “cheap filter“ with irregular glass surfaces MUST always be screwed directly into the eyepiece; otherwise sharpness and definition are reduced, above all when doing observations at high magnification or long-focus photography with an inserted Barlow lens.
About Baader Filter cells
Or: why Baader Filters may "clatter"
Interferogramm of a loosely mounted Baader filter glass
Interferogramm of a tightly locked Baader filter glass
After putting flawlessly performing filter blanks into the standard tightly-screwed filter cells, interferometer measurements revealed drastic deformations caused by the stresses of assembly.
That‘s why all our filters are no longer tightly fixed but held spring-loaded in the filter cell. The filter glass may ever so slightly „clatter“ in the cell, but that neither affects the image quality nor shows a displacement in the final image. A stress-free filter, not tightly fixed in its filter cell, is not a fault and entirely intentional.
Visual observations and astrophotographs obtained with Baader filters are among the best achieved worldwide by amateur astronomers. You may find typical examples using our emission line filters and LRGB filters online, for example at: http://panther-observatory.com/
