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Rock Doctor
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Yet another newbee question, whats the difference between filters for visual and filters for ccds? Looking to buy a set of LRGB for imaging and just wondered if these would be ok for visual observation as well. Also which make Baarder, Astrodon which is a good make and does it make that much difference?


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baader are good filters for the price and loads use them, Stephen uses them....but you are in whole other world with astrodon, they are supposed to be the best but your


credit card would take a big hit :)


 


Sheila


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With ccd imaging you are doing narrow band work - stuff the eye doesn't see - in order to produce primary colours at the camera chip. So using narrow band filters for visual would block out too much visible spectrum to be of use as I understand it. We only see black and white when looking at unfiltered deep sky objects - but the camera on long exposure gathers light in all wavelengths.


 


Looking at the sun in a solar scope through hydrogen alpha filters allows us to see less than half an angstrom wavelength resulting in an orangey red disc. Stars behind nebulae produce a lot of Ha light that only the camera can pick up. The other filters used are O3 and S2 which show blue and green (dunno which way round though).


 


So when you stack subs from a b/w ccd camera they combine the primary colours from each filter to produce a composite colour image. That's my lay understanding Dave - should be enough to help you research further and correct anything daft that I've said lol. :)


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arn`t visual colour filters just really coloured bits of glass / plastic ? cheap ones anyway,


for imaging i use, although not alot at the minute, a set of astronomik lrgb type 2 filters, these were recommeded to me by Olly, and having met the guys that make the at astrofest last year i think i made the right choice, plus you can get all the narrowband filters from astronomik, they are very good quality 


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Thanks chaps. I understand the difference for the narrow band filters but what is the difference for a set of LRGB between those for ccd and visual use and can a set for ccd be used for visual?


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Visual filters dont have to be made to such high standards as imaging ones. With imaging you are opening the shutter for ages thus any imperfections will show up whereas visual dont have to be so great because our imperfect eyesight wont detect the difference. However you can still use an imaging RGB set for visual but its a bit of overkill if thats all your gonna do.


 


I use Astronimik LRGB Ha and OIII for imaging but Antares planetary filters for visual with the addition of a couple of Lumicon visual narrowbands. The Antares set is more than good enough for planets and are very affordable


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