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SOLAR FILTER GUIDE by- AstroShop

 
A guide to selecting and use of our Thousand Oak Solar Filters
 

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.

When attaching the filter to your scope, it must be able to stay attached when the telescope is pointing downward. If not, you can use the supplied felt liners to ensure a snug fit.

ARE THE FILTERS COMPLETELY SAFE? All of our 2+ & 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 3% of the time but having a full aperture filter during such rare events can reallly make a difference to how much you can observe. But for most of the time, "off-axis" reduces the aperture and increases the focal length thus reducing the turbulent effects. We recommend and only offer 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 for 6" to 8" is still preferred, it can be stopped down using a simple mask as conditions dictate.

General Guide to Off-Axis solar aperture filters are listed below:

CLEAR APERTURE

OUTER CELL I.D.

OFF-AXIS 2+

MODEL No.

76mm\3.00" 233mm\9.187" Celestron & Meade 8 S/C

9187A

76mm\3.00" 241mm\9.50" C-8 Newt, Orion Sky Watcher

9500A

76mm\3.00" 247mm\9.75" Meade Starfinder 8, Orion 8 DSE

9750A

76mm\3.00" 254mm\10.00" Meade LXD-55 8 S/NEWT, Tak 212

10000A

76mm\3.00" 266mm\10.50" Coulter 8

10500A

76mm\3.00" 273mm\10.75" StarHopper 8

10750A

76mm\3.00" 273mm\10.75" C-9 1/4

C10750A

101mm\4.00" 292mm\11.50" Celestron 10 Newt, Orion SkyWatcher 10

11500A

101mm\4.00" 305mm\12.00" Meade 10 S/C, LXD-55 10 S/NEWT,

12000A

101mm\4.00" 317mm\12.50" C-11, 10" Dob

12500A

101mm\4.00" 330mm\13.00" Meade Starfinder 10, Coulter 10

13000A

114mm\4.50" 349mm\13.75" Meade 12 S/C

13750A

114mm\4.50" 387mm\15.25" Orion 12.5

15250A

152mm\6.00" 400mm\15.75" C-14

15750A

152mm\6.00" 406mm\16.00" Meade 14 S/C

16000A

152mm\6.00" 432mm\17.00" Coulter 13.1

17000A

152mm\6.00" 447mm\17.62" Meade 16 S/C

17625A

152mm\6.00" 482mm\19.00" Meade DS-16

19000A

Got a scratch on your glass solar filter?

If you find you have scratches on the surface of your solar filter you can simply use a thick, black, permanent marker pen to cover scratches and avoid unsafe light entering the telescope. If you have too many scratches you should seriously consider replacing the solar aperture filter.

 

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