George! Posted September 25, 2011 Share Posted September 25, 2011 On my 250px Primary mirror dust cap there's a circle mini dustcap you can take off. Is that a built in solar filter? Link to comment Share on other sites More sharing options...
ecosse Posted September 25, 2011 Share Posted September 25, 2011 I have Been wondering what this cap is for too don't think it's a filter tho Link to comment Share on other sites More sharing options...
Moonshane Posted September 25, 2011 Share Posted September 25, 2011 hi George - DEFINITELY NOT.this is effectively an aperture mask which reduces the brightness of the moon etc and may increase contrast - that said, it also reduces aperture and resolution. not worth using really but you may be able to buy a solar filter to go over the small hole. Link to comment Share on other sites More sharing options...
George! Posted September 25, 2011 Author Share Posted September 25, 2011 Interesting, thanks! Link to comment Share on other sites More sharing options...
Bizibilder Posted September 25, 2011 Share Posted September 25, 2011 As Moonshane says IT IS NOT A FILTER OF ANY SORT - sorry for the emphasis but I'm sure you want to keep your eyesight!To make a filter that is safe you would need to buy some Baader solar film First Light Optics - Baader AstroSolar Safety Film ND 5.0 and make a filter holder that will go over the small hole in the scope cover - the film is less than A4 in size and therefore not big enough to make a full aparture filter. If you are not very handy you can buy ready made filters that fit over the end of the scope First Light Optics - AstroZap Baader Solar Filter - you will then be using full aparture. These filters are safe.(As an aside NEVER buy or use a so-called "eyepiece filter" - they sometimes come up for sale on fleabay - they will shatter - with obvious consequences.) Link to comment Share on other sites More sharing options...
umadog Posted September 25, 2011 Share Posted September 25, 2011 That cap will cut down the aperture and so increase the focal ratio. This will make everything look dimmer by decreasing exit pupil size. It will also decrease resolution to a significant degree. Maybe useful for solar observing. For lunar observing, either use a neutral density filter, variable polarising filter, increase the power, or just let your eyes adapt to the light and soak in the views. Link to comment Share on other sites More sharing options...
Moonshane Posted September 25, 2011 Share Posted September 25, 2011 useful for solar obs with a filter as mentioned above though (I know you meant this Umadog). Link to comment Share on other sites More sharing options...
umadog Posted September 25, 2011 Share Posted September 25, 2011 Oh yes... Ooops! WITH filter in front of the hole. Link to comment Share on other sites More sharing options...
Stephen Posted September 25, 2011 Share Posted September 25, 2011 If you're going to go solar, don't use the cut down aperture. Get a big enough sheet and make a mask for the whole aperture - miles better in my opinion Link to comment Share on other sites More sharing options...
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