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gaidash
super member
Reged: 12/19/09
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OIII CCD vs visual
#5194707 - 04/28/12 11:08 AM
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I am a newbee to filters, so here's a simple question, can a OIII ccd filter be used for viusla?
Thanks!
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David Knisely
Postmaster
Reged: 04/19/04
Loc: southeastern Nebraska
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Re: OIII CCD vs visual
[Re: gaidash]
#5195455 - 04/28/12 07:33 PM
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Quote:
I am a newbee to filters, so here's a simple question, can a OIII ccd filter be used for viusla?
Thanks!
It can be, but the results for some OIII CCD filters may not be quite as good as one intended for visual use. The CCD version from Baader tends to be narrow (8.5 nm FWHM) to highlight the 5007 angstrom line and may not have quite the peak transmission as some of the OIII filters that pass both OIII lines at nearly their full intensity. The one from Astronomik is a bit broader (12 nm similar to that of the Lumicon OIII), but it is unmounted. Clear skies to you.
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tomcody
professor emeritus
Reged: 07/06/08
Loc: Titusville, Florida
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Re: OIII CCD vs visual
[Re: David Knisely]
#5196447 - 04/29/12 12:04 PM
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Another simple question: For visual use, can an OIII filter be used with a small (4") refractor?
I have read conflicting statements, most say that an OIII needs a larger aperture.
Rex
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David Knisely
Postmaster
Reged: 04/19/04
Loc: southeastern Nebraska
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Re: OIII CCD vs visual
[Re: tomcody]
#5196595 - 04/29/12 01:45 PM
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Quote:
Another simple question: For visual use, can an OIII filter be used with a small (4") refractor?
I have read conflicting statements, most say that an OIII needs a larger aperture.
Rex
Yes, an OIII filter can indeed be used in a small refractor, although with some refractors that have longer focal lengths, it can be difficult to get into the optimal power range for the OIII (from 3.5x per inch to 9x per inch of aperture with somewhat better performance in the lower half of that range). Larger scopes will show more objects that the OIII will work on (and will show more faint detail in them) than a smaller one, which is one reason a larger scope is often recommended, but that does not mean the OIII is not useful in something like a 4 inch. The old "OIII isn't useful in apertures smaller than 8 inches" is just a myth created by those who haven't fully researched and observed sufficiently with an OIII filter to discover the truth. I have used my 2" OIII stuck in the front of my 9x50 RACI finderscope to view both sides of the Veil Nebula at the same time (that is a *two inch aperture*). Indeed, one of the best views I get of the North America Nebula is with my 100mm f/6 refractor at 15x and 25x using the 2" Lumicon OIII filter. You do have to use the proper power range, get properly dark adapted, and use averted vision for the OIII to work well, but it can indeed be used in smaller scopes. Clear skies to you.
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tomcody
professor emeritus
Reged: 07/06/08
Loc: Titusville, Florida
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Re: OIII CCD vs visual
[Re: David Knisely]
#5196889 - 04/29/12 04:38 PM
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David,
Thank you for that great explanation.
Rex
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gaidash
super member
Reged: 12/19/09
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Re: OIII CCD vs visual
[Re: David Knisely]
#5198297 - 04/30/12 01:30 PM
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Thanks, it was exactly Baader CCD that I was thinking to buy for visual use...
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