Thousand Oaks Optical - Full Aperture Glass Solar Filter Type 2+ for Celestron C-9.25 Telescopes
Type 2+ : Made with high quality hand select glass coated with our exclusive Solar II Plus. The most durable glass filter on the market. Guaranteed fifteen years.
- Filter Transmission: RG, Black Polymer & Glass: 1/1,000th of 1% (Optical Density 5). Great for both visual and photographic use.
Frequently Asked Questions:
- WHICH TYPE IS THE BEST OPTICALLY? The RG film offers the highest resolution with high magnification. The glass is a very close second. Under low to moderate magnification, it's difficult see the difference between RG, Glass or Black Polymer.
- WHAT SIZE DO I ORDER? The application table below lists sizes by clear aperture (filter size) and outer cell wall inside diameter (I.D.) The I.D. of the cell slips over and around the O.D. of the telescope tube or lens holder. If you do not see your brand and model, simply choose the closest outer cell I.D. size larger than the outside diameter measurement of your instrument. Example: part # 4250 (4 1/4") would fit O.D. measurements from 4" to 4 3/16". Do not choose a size the same as your O.D. since it will be too tight and not allow room for a felt lining. Ample felt is included for custom fitting.
- ARE THE FILTERS COMPLETELY SAFE? All of our Glass 2+, RG-Solar Film & Black Polymer filters are completely safe for unlimited visual use. If handled with care and common sense, all will last a minimum of 20 years to life.
- CAN THE TELESCOPE OPTICS GET HOT OR DAMAGED? No, all the heat and intense light is blocked before it can enter the telescope. Your telescope may get warm from sunlight shining on it, not from the small amount of visible light transmitted through the filter.
- WHAT DETAIL IS VISIBLE? Sunspots and surface granulation are the two main features. The only detail that cannot be seen with a standard filter (commonly called white light filter) are prominence and flares which require our highly specialized H-Alpha filter system.
- FULL APERTURE VERSUS OFF-AXIS (REDUCED APERTURE): For telescopes up to 5" aperture, off-axis is not an advantage. Larger apertures suffer more from daytime atmospheric turbulence. This turbulence is magnified by the aperture. Perfect daytime "seeing" only occurs about 1% of the time. Off-axis reduces the aperture and increases the focal length thus reducing the turbulent effects. We recommend off-axis for 10" and larger telescopes. The solar image is not darker with reduced aperture as we allow for this in the coating density. When viewing through the eyepiece, the field of view is not reduced; it looks the same as full aperture. If full aperture is still preferred, it can be stopped down using a simple mask as conditions dictate.
- WHY ARE THREADED CAMERA FILTERS ONLY AVAILABLE IN BLACK POLYMER? Rg and Glass filters have highly reflective coatings that can cause internal reflections between the filter and camera lens since the filter and lens are in close proximity. This problem is less likely to occur with telescopes, however, mounted telescope filters can be tilted slightly to move any internal reflections off the central axis and out of view.
Type 2 Plus: Made with high quality hand select glass coated with our exclusive Solar II Plus. The most durable glass filter on the market. Transmission is 1/1,000th of 1% (Optical Density 5). Great for both visual and photographic use. Solar image is yellow-orange. Guaranteed fifteen years.
|Name||TO - Full Aperture Glass Solar Filter TYPE 2+ for Celestron C-9.25 Telescopes|
|Manufacturer||Thousand Oaks Optical|
|Outer Cell ID||273mm\10.75"|