A place for general chat about Sky at Night Magazine


Postby jackamar » Sat Jan 26, 2013 7:30 am

Any idea what type of filters i require so i can block out some light or can i get a small set.
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Re: filters

Postby Joycesmith » Fri Oct 27, 2017 12:16 pm

Optical filter is a device which selectively transmit lights in a particular range of wavelength. Filters mostly of two types absorptive filter and interference filters. Absorptive filter is absorb some wavelengths of light while transmitting others. Interference filter is reflect the unwanted portion of the light and transmit the remaining.
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Re: filters

Postby Aratus » Tue Oct 31, 2017 2:18 pm

Basically, filters reduce the brightness of the image through the telescope. The moon can be rather too bright to look at through a telescope, so a neutral density filter, or 'moon filter' can be quite useful. Venus can be too bright in certain circumstances too. In all other cases filters try to dim different parts of the image more or less than other parts, thus increasing contrast. For instance a light blue filter will darken Jupiter's 'Great Red Spot', but leave the rest of the planet less dark. Some filters try to darken the sky more than the object you are looking at. Light pollution filters and nebula filters try to do that. A set of colourful filters look quite impressive, but I predict they won't get used often.
I use an 11" Celestron SCT (CPC 1100) on an equatorial wedge, housed in a 2.2m Pulsar observatory. I use a ZWO ASI1600MC and Canon 500D for imaging.
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