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Equipment Discussions >> Eyepieces

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Starman1
Vendor (EyepiecesEtc.com)
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Reged: 06/24/03

Loc: Los Angeles
Re: OIII Filter Choice new [Re: Scanning4Comets]
      #5682253 - 02/15/13 07:56 PM

Markus,
I think David linked to a review of that very filter a couple posts ago.
DGM filters come from Omega.


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Jon Isaacs
Postmaster
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Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: OIII Filter Choice new [Re: Starman1]
      #5682263 - 02/15/13 08:03 PM

Quote:


I think it is up to guys like you and me to point out the bandwidth issues of the filters that are out there, but also to ask what it is the observer is hoping to accomplish. Not everyone is going to prefer exactly the same filter choice under all conditions and on all nebulae.




Don:

I use an O-III filter when I want to maximize the nebulosity, the Orion Ultrablock when I want to balance the nebulosity and the starfield. My one nighter with the TV O-III leads me to believe the TV filter is more of a UHC filter than an O-III filter.

Jon


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David Knisely
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Reged: 04/19/04

Loc: southeastern Nebraska
Re: OIII Filter Choice new [Re: Jon Isaacs]
      #5682685 - 02/16/13 12:53 AM

Quote:

Quote:


I think it is up to guys like you and me to point out the bandwidth issues of the filters that are out there, but also to ask what it is the observer is hoping to accomplish. Not everyone is going to prefer exactly the same filter choice under all conditions and on all nebulae.




Don:

I use an O-III filter when I want to maximize the nebulosity, the Orion Ultrablock when I want to balance the nebulosity and the starfield. My one nighter with the TV O-III leads me to believe the TV filter is more of a UHC filter than an O-III filter.

Jon




The Tele Vue is a narrow-band filter in terms of raw FHWM bandwidth, but the location of that passband is centered on the OIII lines and not between the OIII and H-Beta lines as is done with a true narrow-band nebula filter. I still prefer the DGM NPB to the Tele Vue OIII, as it has a similar bandwidth, sharper edges, and, in addition to passing the OIII lines, lets through the H-Beta line at a high level of transmission rather than excluding it as the Bandmate "OIII" does. For a true Oxygen III nebula line filter, I would definitely prefer the Lumicon OIII or Thousand Oaks LP-3 OIII filter. Clear skies to you.


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David Knisely
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Reged: 04/19/04

Loc: southeastern Nebraska
Re: OIII Filter Choice new [Re: Starman1]
      #5682707 - 02/16/13 01:17 AM

Quote:

David,
Since you are still logged in to this thread, you might be interested in my notes from last Saturday night in which I viewed NGC2359, "Thor's helmet",
with both the Lumicon O-III and TeleVue O-III filters.

As you would expect, the narrower bandwidth of the Lumicon displayed more nebulosity--3 distinct "tails" away from the central bubble, striae within the bubble, and some 'clouds' away from the main body a bit. A very spectacular view of the nebula.

The TeleVue filter did not show the level of contrast--the background was lighter, and the 3rd extension from the central bubble was hard, and the outer 'cloud' of nebulosity wasn't seen.

BUT, the number of stars in the field of view with the TeleVue filter was similar to the non-filter view--very rich with stars.

Esthetically, I couldn't say which I preferred the most. The 12.5", under very dark skies (SQM21.7) showed a lot of stars in the field even with the Lumicon filter. But the overall impression of the field with the TeleVue filter was most impressive, even if the very faintest nebular details weren't as obvious. And the TeleVue also showed M46 and its associated planetary better than the Lumicon (the stars were a lot brighter).

Comparing a lot of filters recently on a number of nebulae, I'm coming to realize that there is room for different filters to be used on different objects.
M42, for instance, was far more colorful to me with a Baader UHC-S than with the Lumicon UHC. The red wavelengths transmitted and the slightly broader main passband of the Baader really matched well with that object.
On M27, though, the Lumicon was definitely preferred, revealing ropy tendrils in the outer nebulosity far better than the Baader.

I think it is up to guys like you and me to point out the bandwidth issues of the filters that are out there, but also to ask what it is the observer is hoping to accomplish. Not everyone is going to prefer exactly the same filter choice under all conditions and on all nebulae.




If I want to see stars with a little nebulosity, I will use a good broad-band LPR filter like the Orion Skyglow. It is a tad narrower than the Lumicon Deep-sky and will provide a bit more contrast in emission nebulae without hurting the stars much at all. In fact, I prefer that filter for reflection nebulae like the Merope Nebula or the Iris Nebula. However, for emission nebulae, I want to see nebulosity and not just stars. For that, clearly, a narrower filter is needed. The Tele Vue OIII has the narrower passband (about 240 angstroms FWHM) but it isn't centered properly. Its transmission of the H-Beta line is only 28.8%, and the profile of the passband is more of a Gaussian form than something sharp. The DGM NPB has about the same FWHM passband width, so its effect on stars should be similar to that of the Tele Vue OIII. However, its transmission at both the OIII and H-Beta lines is around 94%, so it will enhance nebulosity that happens to have either a balance of OIII and H-Beta or just H-Beta. For my money, as a single purchase, the DGM NPB is a much more effective filter than the Tele Vue Bandmate OIII. In the case of true Oxygen III filters, stars are again not an issue. When making the choice to use an OIII filter, you are going after the maximum contrast, so you want a filter that lets through only the OIII lines and little else. Indeed, when under some skyglow, on some nebulae like the Dumbell, I will often switch to an OIII rather than use my narrow-band filters just to be able to see the object with more contrast. For that, again, the Tele Vue Bandmate OIII is an also-ran. It is just too much of a compromise in design. Clear skies to you.


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