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What's the actual size of your 2" filters in "mm" with and without frame/ring? What step down adapter is suggested from a 52 mm to "-- mm"?
Question by: Waqas Ahmad on Oct 10, 2016 7:54:00 PM | 1 Answer(s)
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The Baader L-RGB-C CCD Filters
A brief introduction to the function of CCD Filters Without modern RGB-filters, the CCD-revolution in astronomy would never have happened. It´s these filters that allow schools and universities do do meaningful imaging in science and education under totally light polluted skies from the midst of major cities. Unlike terrestrial objects, astronomical objects shine in discrete emission lines. For this reason, any RGB-filter design with gently raising and falling slopes on either side of the transmitted spectral region generally is undesirable. The stars themselves obey to the laws of physics and shine by their stellar temperature colour - with a smooth, wide spectrum. This richness of colours can be covered nicely when adding an L-filter into the imaging process. However - shades and colour hues such as in earthly objects are not available when imaging the sharply defined emission spectra of deep sky objects. For this reason the slopes on RGB filter curves ought to be produced extremely steep for each colour channel - for maximum energy collection efficiency, while maintaining maximum contrast between the individual spectral emission lines. Peak transmission of Baader RGB filters are extremely high but at the same time encased tightly within each of the three colour channels - with a very important and deliberate overlap between the B...
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Baader Narrowband Filter – why?
A brief introduction to the function of narrow band filters. Narrowband filters have revolutionized CCD photography for the “amateur astronomer” in the past decade in incredible ways. It was now possible for small telescopes, even in light polluted city areas, to photograph faint nebula – and generally the universe surrounding us in the incredible variety of coloured “gaseous areas” – in hours of exposure time, and by combining the exposure of each colour of the various emission lines – even the faintest nebula were suddenly registered despite strong light-polluted skies. Suddenly, the smallest backyard telescope can collect the real light of gaseous nebula to produce image results there were otherwise only reserved for telescopes with several meters of light-collecting surface without any time limit. The narrow emission area and spectral half width of these filters ensures that only the light emitted or reflected from the gaseous nebula literally “punches” through, even from light polluted city and bright sky background. The stars, which would otherwise outshine the light of the nebula completely, remain tiny. The final image now succeeds colour composites (consisting indeed only from the many hours of collected photons) and is much better, you can even conclude with an...
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Information about Baader Filters and Filtercells
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. 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...
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Off-standard single filter sizes from Baader - why not:
Quite often we receive requests for a single filter in an off-standard size. In all cases we are sorry that we must answer as follows:
Sorry (we know it would be so very much cheaper in production - and we would be so much more flexible to fill special requests) - but we have decided long ago to not cut or saw our filters from large plates because this would leave the coating stack open and mutilated (with microscopic cracks) all around, prone to aging and peeling.
Many times we had the chance to inspect our competitors filters after several years of use (due to our 30+years of servicing SBIG-CCD-cameras/and filter wheels) and we realized already 15 years ago how moisture and heat stress can deteriorate even most modern hard coatings, slowly peeling off from the carrying substrate over time, unless the coating stack is sealed all around the filter stack.
As a consequence - in order to create our filters to remain impermeable - we only offer all filter substrates already cut to final shape and run each substrate on an double deck auto-polisher to achieve perfect optical flatness and freedom from cone errors.
Then we do individually coat these substrates in 500 pc per run as minimum to fill a complete coating chamber, in a way that the coating stack (many times 50+ layers) applied onto each filter won't reach to the very edge of the round or square substrate, so that the coating stack remains completely sealed from all sides. In this way we can ensure that our filters will not age at all.The sad effect is that we cannot offer other sizes unless the inquired production quantity were in the range of 250 to 500 pc (depending on size) and the tooling rings or square holders will be paid for, which serve to precisely center each individual filter substrate within the rotating calotte inside the coating chamber. Sorry - as explained above - we just will not coat onto large plates and cut any shape from them, also because such large plates cannot be polished optically flat in the same way we do it.
For your most urgent need and for single piece solutions we can only recommend to order the next larger size of our respective filter and have that cut to shape by an ophtalmologist locally. We can supply the round filters without the metal cell in such cases; square filters come without cell in any case.
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Unmounted Filters – which side should face the telescope?
Question in Detail:
I just bought LRGB 36mm unmounted filters. I have question: which side of filter should be placed towards telescope? Is it better way of distinguish than "more shiny surface towards telescope"?
Answer:
Always put the more reflective side towards the telescope side. To guide you we already put a small arrow on the filter rim, on those filters were the position matters. This arrow indicates which face of the filter should be directed towards the sky (telescope-sided). All cell-mounted filters are already oriented in a way that the most appropriate filter face is facing the sky when the filter would be mounted directly onto the front end of the nosepiece of a camera.
If you mount your filter the other way, any reflected light would have a short way to the camera sensor, resulting in a higher risk of getting some kind of back-reflections inside the camera field. Many sensors have highly reflective areas near to the light sensitive area, also the area with the bonding contacts is sometimes highly reflective.But: this is true only for instruments without optical elements near to the focal plane. If you have f.e. a coma corrector, field flattener, focal reducer, focal extender (to a lower degree due to concave surface), or in extreme cases a whole lens group for more complex field corrections a few centimeters in front of the filter it could be useful to flip the filter against the rule from above (thus having the arrow pointing away from the telescope). Cause in such cases the likelihood of reflections from the sensor could be lesser then fort- and back- reflections from such glass-surfaces. If in doubt, it helps to make some test images from a star field with bright stars, using the filter in both ways for comparison.
Should you really have some reflections with both positions it can be more effective to add a spacer between filter and camera, eventually shifting the reflection out of the image field. With focal correctors having curved surfaces changing the filter-lens distance could help also.
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