C-7 Home Page
Products & Services
Solarscope Index Distribution News Notes & Interesting Articles Pricing Products Warranty & Service
SF and DSF SERIES HYDROGEN-ALPHA FILTERS BY SOLARSCOPE LTD.Not suitable for viewing or imaging objects other than the Sun
Solarview SV-50 50mm Aperture Hydrogen Alpha Filtered f/8 Telescope Optical Tube Assembly
Solarview SV-60 60mm Aperture Hydrogen Alpha Filtered f/8 Telescope Optical Tube Assembly
Above image: The Sun by Pete Lawrence, image taken on 2 June 2010 with a Solarspectrum SF-70 'Double Stack' Hydrogen-alpha filtered telescope (146,699 bytes).
Overview: The Solarview Ltd. SF/DSF series of tuneable Fabry-Perot etalon based filters have become known among the more astute in our astronomy community as the 'Rolls-Royce' and 'Ferrari' of this class of hydrogen-alpha (HÅ) solar filters, featuring first rate craftsmanship and no cost cutting compromises in materials or design. The Solarscope series products have been developed to satisfy those who prefer to carry or travel with a smaller solar telescope, even if paying a premium for it, but that can equal or outperform much larger diameter solar filters of lesser quality. Sure, Company Seven sells competing solar telescopes and filters some that cost one-third the cost of a similar aperture Solarscope, but no similar arranged filter can deliver the fidelity of the views seen or images captured by the Solarscope. Especially when observing under adverse climactic conditions, you will appreciate the thermal stability of these filters. Clientele who select our Solarscope Ltd. products seek to be mightily impressed, but yet do not wish to work too hard while doing so. And those who choose to buy from Company Seven, are the most demanding of the Solarscope clientele in the Americas.
Right: Solarscope 0.7Å SF-100 and 0.5Å DSF-100 stacked filters attached and ready to go attached to a TeleVue NP-101 telescope and mount (38,031 bytes).
but yet do not wish to work too hard while doing so." Martin Cohen
The Solarscope SF/DSF series filters turn your telescope, whether typically employed for astronomy or for terrestrial work (panoramic, nature watching, spying on neighbors, etc.) into a first rate solar telescope. With a Solarscope SF / DSF set, any astronomer can observe day and night - around the clock! The filters pass light only at one narrow portion of the spectrum centered on the HÅ line at 6562.8Å where solar features including prominences and sunspots show well to the eye and to cameras as well.
Critical aspects of these filters include:
Above: at left is the Solarscope 0.7Å SF-70 filter set attached by means of an aluminum thread adapter onto a TeleVue 76 telescope and mount at Company Seven.
At right are both the Solarscope 0.7Å SF-70 and 0.5Å DSF-70 stacked filters with the blocker (blue banding) attached to a TeleVue 76 telescope (109,731 bytes).
Click on image to see enlarged view (339,936 bytes).
Etalon: The basis of the Solarscope etalon is a matched pair of ultra fine pitch polished, accurately figured λ/100 fused silica plates (thermally stable and costly material), with partially reflective, low absorption coatings for 656.28nm on the front faces and anti-reflector coatings on the back faces. The etalon assembly has optically contacted spacer pieces of very precise thickness, uniformly arranged around the etalon plate periphery to provide maximum rigidity and stability for the air gap. The etalon spacers are cut from low thermal expansion material, polished and figured to high levels of surface flatness and parallelism. When the etalon construction and optical contacting procedure is complete, the tuned etalon assembly is resiliently mounted into a cell designed to afford shock protection and freedom from stress. Solarscope currently offers four highly perfected different sizes of etalon: 50mm, 60mm, 70mm and our top of the range 100mm.
The Solarscope SF-xxx filters consist of a single stack etalon filter with a matched blocker that is nominalized with the matching blocker to transmit a narrow 0.7Å bandpass. The DSF-xxx series are 'double-stack filters' that allow the user to operate with the SF-xxx component alone 0.7Å or the two forward-mounted etalon elements can be combined with their blocker to transmit an even narrower 0.5Å bandpass. The narrower the bandpass, the more contrasting the details on the disc of the Sun will appear. At the wider the bandpass the features that are cooling as they clear the disc of the sun and move off the center band (most notably prominences and spicules) will appear more distinct.
Bigger Is Better - Usually: the comparative light gathering power of systems of similar quality, their ability to show images in terms of how bright they may appear, is better for a larger diameter lens that a smaller lens. The resolving power, or the capacity to reveal finer and finer details, is dependent on 1. quality of the lens - how well and uniformly the system transmits light without noticeably taking away from the image sharpness and without introducing distortion or other problems, and 2. overall lens diameter, and 3. 'seeing' conditions of steadiness and transparency in the atmosphere. Each of the Solarscope hydrogen-alpha filters can provide views of the Sun that will simply stun the public with their clarity and at times showing a three-dimensional appearance of structures and details on the Sun. The larger diameter the filter however, then not only will more details be seen on the better days but owing their increased brightness the faster exposure times will be practical thus helping to freeze moments of seeing; you will be more likely to acquire similarly stunning photos of the solar activities.
Right: Graphic by Company Seven demonstrating differences between circles of 50, 60, 70 and 100 mm diameter (17,153 bytes).
When considering the differences in area between the Solarscope filters we can see how the area of a 50mm diameter filter is 1964 sq. mm, while that of a 60mm diameter filter is 2827 sq. mm, or 1.4 x that of the 50mm. The area of a 70mm diameter filter is 3849 sq. mm, or 1.4 x that of the 60mm model. That of the 100mm is 7854 sq mm, or 2.0 x that of the 70mm model. The resolving power differences of each should be proportional to their diameter (aperture), so the 60mm model will provide an increase in detail by a factor of 1.2x, the 70 will provide 1.4x increase over the 50 and 1.2x that over the 60. While the 100mm filter should show twice the details of a 50mm filter, 1.7x that of the 60, and 1.4x the details possible with the 70mm model.
Blocker: Each is provided with a required matched 30mm Blocking Component that attaches at the rear of the telescope. The system cannot be employed without the forward and matching rear mounted blocker working together. By default, this filter is housed in a standard 2 inch diameter slide-in housing with a female 2 inch port to accept an optional precision mirror diagonal with eyepieces, or camera attachment hardware, or other accessories. A low profile 2 to 1-¼ inch reducing adapter is included as standard, so you will maintain the capability to use either 2 or 1-¼ inch accessories. Solutions are available for 1.25" fittings as well but Company Seven prefers to see customers maintain the best versatility by accepting the 2 inch arrangement; please inquire for further information.
Right: Solarscope Blocking filter component as provided, one for each 0.7Å SF-xxx and 0.5Å DSF-xxx filter (38,031 bytes).
Choice Of Telescope: The SF-DFS filters are ideally attached to a well made refracting telescope arrangement; this is compatible with fast or slower f-ratio telescopes. However, while Solarscope recommends the telescope focal length should be less than 3,000mm, Company Seven teaches that for best versatility of accessories, and for accommodating and adapting to a broad range of 'seeing conditions' Company Seven recommends telescopes of 500 to 650mm focal length. One can always incorporate an optional negative (Barlow) lens behind the blocking filter element; candidates include our Baader Flat Field Teleconverter, or the TeleVue Powermate series lenses, or the Astro-Physics Advanced Barlow.
These filters are not inexpensive, and they can be surprisingly heavy components to put onto a small telescope. So Company Seven recommends using the SF/DSF filters only with the most well suited telescopes, ones with precision machined front cells and threads to accept the filter directly or with optional threaded adapter as opposed to any slip-on arrangement. For examples Company Seven recommends using the SF-70/DSF-70 filter with either a TeleVue 76 or 85 telescope with an adapter plate. We recommend using the SF-100/DSF-100 filter with either a TeleVue NP-101 or 102 telescope since the DSF-100 filter can be threaded directly onto these telescopes and with no need for adapter plate. Company Seven sold the Astro-Physics 105 "Traveler" telescopes when these were in production (we continue to be the only full line retailer of Astro-Physics in the Americas), and we can source them and required adapters for clients who may prefer one for use with their DSF-100.
Above: Solarscope SF-50 filter threaded onto a fully machined adapter, with this assembly threaded onto a TeleVue 76 telescope.
The matched Blocker is at the rear, just barely visible (46,757 bytes). You may employ a telescope that has an aperture at least as large,
or even larger, than the diameter of the SF / DSF filter aperture. This avoids vignetting the Solarscope filter.
The SF/DSF are filter sets that attach onto a suitable telescope; this arrangement relies on the customer or Company Seven to provide a suitable telescope optical tube. Ideally the telescope of choice will feature:
Above: at left are fully machined slip fit adapters, made to adapt a thread on SF / DFS filter onto the Dew Shield or front Lens Cell of a telescope.
At right is a fully machined thread-on adapter at Company Seven, made to adapt a thread on SF / DFS filter onto the threads of the front Lens Cell of a telescope (34,008 and 36,798 bytes).
Click on images to see enlarged views (58,611 and 67,800 bytes).
Assembly And Tuning: There is some assembly required of the SF and DSF systems in the field, only minutes really, but it is worthwhile to read the documentation provided with each filter by Solarscope and also read the illustrated manual written by Company Seven so that you avoid making what may be a costly mistake, and that you get the best performance out of your new Solarscope too.
Right: Solarscope DSF-100 filter set as provided with case. This includes the 0.7Å SF-100 and 0.5Å DSF-100, with their matched Blocker components,
The SF etalons and Blocker used to provide a bandpass of 0.7 Angstrom are ideal for viewing a good balance of both surface and prominence detail. A thumbwheel tilt mechanism is provided to allow you to adjust the tuning of the etalon slightly. This may come in useful to study material which has been ejected from the Sun's surface at such a speed that the light it emits has been (Doppler) shifted slightly away from the main h-alpha wavelength. The 0.5 Angstrom configuration will be preferred when seeking out finer details on the disc of the Sun, and for imaging these features.
Left: Solarscope SF-100 and DSF-100 filters at Company Seven showing their tilt set screws (34,459 bytes).
All that is involved in putting a Solarscope filter into service is to attach balance the telescope optical tube in anticipation of adding the weight of the front-mounted SF / DSF filter housings. Slip fit (or thread-on) the appropriate Blocker filter onto the focuser of the telescope. Attach the desired eyepiece or camera. Then attach the SF-xxx filter onto the front of the telescope. Now double check the balance of the telescope/filter on the mount. Each SF and DSF filter housing incorporates a mechanism, driven by a manually operated set screw, to tilt the etalon within to compensate for changes in atmospherics or Doppler work. After attaching the SF-xxx, move the telescope to center it onto the Sun and observe through the eyepiece while adjusting the focuser until the solar disc edge is sharp and well defined. Next, while observing through the eyepiece address the tilt setting screw at the front mounted SF-xxx filter; adjust this clockwise or counterclockwise until the image is most clear and contrasty. Now you are set for operation at 0.7Å
To operate at the narrower 0.5Å configuration, move the telescope so that it is pointed well away from the Sun. Carefully remove the SF-xxx filter and also remove the Blocker, taking care not to disturb the etalon tilt setting screw. Replace the 0.7Å Blocker with the 0.5Å Blocker. Attach the DSF-xxx filter (the one in the all black anodized housing) onto the front of the telescope. Then attach the SF-xxx filter onto the front of the DSF-xxx unit again taking care not to disturb the tilt setting screw of the SD-xxx. When the arrangement is correct then the red lens of the SF-xxx will still be at the front facing the Sun as shown in the image at top right of this page. Again check and adjust the balance of the telescope/filter on the mount. Finally, while observing through the eyepiece address the tilt setting screw of the DSF-xxx filter (black housing) only; adjust this clockwise or counterclockwise until the image is most clear and contrasty. Now you are set for operation at 0.5Å. The "Solarscope Ltd. DSF-xxx Addendum By Company Seven" contains much more information and advice about how to do this. But you can see this is an operation that with practice can have your Solarscope system up and ready to go in a matter of minutes.
Above: at left are the Solarscope SF single Etalon 0.7Å 50mm, 60mm and 70mm filters; the forward most components distinguished by their natural aluminum housings.
Center shows the cased 0.7Å double stacked Etalon 0.5Å set. At right the 0.5 double stacked Etalon 0.5Å set (27,790 then 55,033 and 59,569 bytes).
We invite you to contact Company Seven, preferably by telephone or by E-Mail, to discuss what filter system may best suit your goals.
SPECIFICATIONS OF THE SF AND DSF SERIES FILTER SETS
† Provided by Company Seven to our customers in the Specifications Table of the Instruction Manual Addendum by Company Seven.
* Company Seven can provide a custom and ATA shipping-approved custom case specifically tailored for your SF/DSF filter set and any other accessories you wish to carry (camera, adapters, eyepieces, etc.).
FOR FURTHER READING
Above Right: Another stunning and informative single exposure processed to reveal a Filament near the limb of the Suns disc demonstrating how these transition to a Prominence, appearing to project off the edge of the Sun. Image taken 21 October 2010 at 11:49:15 GMT by Pete Lawrence for Solarscope with a Solarscope DSF-70 filter configured for 0.5Å operation attached to a 4 inch Apo refracting telescope (70,502 bytes).
Contents Copyright 2012-2013 Company Seven & Solarscope Ltd. - All Rights Reserved