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Equipment Discussions >> Eyepieces

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reiner
sage
*****

Reged: 09/28/05

Loc: Freiburg, Germany
Re: OIII Filter Choice new [Re: MadHungarian]
      #5435465 - 09/23/12 03:42 AM

Quote:

... so is there any way of finding out if the filter bandwith actually has changed or whether the 12nm figure it mentions is just a webpage mistake?




It is no mistake, there was a change. A friend of mine has tested older and newer versions of the Astronomik OIII (and the Baader/Celestron). Check his results here (you might need to ask him for the manufacturing dates or write directly to Gerd Neumann at astronomik.com)

http://www.blackskynet.de/bandpassfilter.html

It looks like the position of the pass band is not ideal, at least not with his sample of the Astronomik OIII. Furthermore, it looks like even some of the major manufacturers have problems to get their filters reproducibly straight.

I have to say that I have tested 8 Lumicon filters (mine and my club's filters) with a professional UV-vis spectrophotometer (some are displayed on this webpage http://www.astroamateur.de/filter/), and haven't observed such "outliers", all of them were perfectly within the specs.


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Traveler
Pooh-Bah


Reged: 08/19/07

Loc: The Netherlands
Re: OIII Filter Choice new [Re: reiner]
      #5435568 - 09/23/12 07:15 AM

What do you mean Reiner, with older and newer? Is older 3 years or something?

Very informative graphics.


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Paul G
Post Laureate
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Reged: 05/08/03

Loc: Freedonia
Re: OIII Filter Choice new [Re: David Knisely]
      #5435866 - 09/23/12 10:51 AM

Quote:

This is an often-quoted myth and is definitely *not* true. As I have stated in the past, I have used the OIII in apertures of 50mm and larger with good results. Indeed, one of my favorite views of the North America Nebula comes in my 100mm aperture f/6 refractor at 15x and 25x using the OIII filter, so it definitely does work in smaller scopes. The larger the aperture, the more objects (and detail) will be visible that the OIII will help with, but this does not mean that its use is limited to apertures larger than six inches. It would be nice if Astronomik would not continue to perpetuate this myth. Clear skies to you.




Same here. I have an older (late '90's) Lumicon OIII. With my 105mm f6 refractor and an appropriate eyepiece I get a gorgeous view of the Veil.

David, how do the newer Lumicons compare to an older one like mine? The label on the back of the plastic case says:

<<< PREMIUM
Nebula Line Transmission %
Oxygen - III 496nm 94
Oxygen - III 501nm 95
Hydrogen-Beta 486nm 0.3 >>

The label is pre-printed with the exception of the transmission % numbers at each bandwidth and the word Premium which are hand written in ink. I assume they tested each filter and sold as premium those with the better actual measurements. My Deep Sky is similarly labeled with an additional line for transmsision at 491nm handwritten in.


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KidOrion
scholastic sledgehammer


Reged: 07/07/07

Loc: Carbondale, IL
Re: OIII Filter Choice new [Re: David Knisely]
      #5435877 - 09/23/12 10:59 AM

Quote:

turtle86 wrote:

Quote:

No sarcasm taken, but I was actually talking about the quality of the stars being seen, not the quantity. I used to have one of the older Lumicon OIII filters, but the stars were bloated or halated.




Those were the very old laminated filters. Lumicon no longer uses that method of protection. In addition, Lumicon's OIII no longer has the "red leak" secondary passband, so the images of stars tend to be not terribly "bloated" or having red secondary star images anymore (at least mine doesn't). Clear skies to you.




David--

About what year did Lumicon make the switch? My Lumicon O-III is late 80s/early 90s vintage, and it seems to have considerably degraded over time to where I can no longer get pinpoint stars through it.


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drollere
Pooh-Bah
*****

Reged: 02/02/10

Loc: sebastopol, california
Re: OIII Filter Choice new [Re: Starman1]
      #5436049 - 09/23/12 12:49 PM

Quote:

The point to be made here is that a slightly narrower bandwidth would enhance the contrast more, but at the expense of the stars. So which do you use the nebula filter for--nebulae, or views of stars? I'm not being sarcastic because there really is a difference in preference involved.




it's worth noting as context that nearly all nebulae are structurally involved with stars, either stars the nebula has recently created or the star that created the nebula. nebulae without stars do not appear in the visual wavelengths, unless they are involved with enough dust to block light. it might make sense to block out stars entirely, if that gave a better image of gas structure inside the nebula, but i wouldn't prefer that because it censors the associated stars that are essential to grasp the nebula context.

this detailed discussion of bandwidth an interesting example of how a complex issue can become displaced by a focus on narrow technical criteria. if the application is photography, then the choice of filter would depend on what other filters (if any) are used to build the final image, and what the image will be used for; if the application is visual, then the choice might be called esthetic. a transmission profile by itself won't decide the issue; you may have to look for yourself.

the OP focused on M97 as the criterion object, which to me is not dramatically enhanced by an OIII filter.


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rick-SeMI
sage


Reged: 01/08/11

Loc: Michigan - USA
Re: OIII Filter Choice new [Re: KidOrion]
      #5436067 - 09/23/12 01:02 PM

Thanks for all the good info.
It helps me decide which OIII to choose.
But, if I were to use the waveform graphs in my post #5432706, I would choose, according to the graphs.
Using O-III Group A because the filters in Group B transmission characteristics bottom out around 90%.
1) Televue - because it allows 496 and 501 nm at 100% transmission and almost flat towards the violet and red spectrum.
2) Astronomik - 496 just below 97% and 501 99%
3) Lumicon - 496 at 99% but clips 501 around 90%

I have the Orion Ultra Block and DGM NPB (Nebula) filters.
The graphs for these two are similiar to a couple of the OIII filters

So, anyone want to take on the question of which would be better for M-97, the Owl Nebula ?


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David Knisely
Postmaster
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Reged: 04/19/04

Loc: southeastern Nebraska
Re: OIII Filter Choice new [Re: rick-SeMI]
      #5436182 - 09/23/12 01:58 PM

Quote:

Thanks for all the good info.
It helps me decide which OIII to choose.
But, if I were to use the waveform graphs in my post #5432706, I would choose, according to the graphs.
Using O-III Group A because the filters in Group B transmission characteristics bottom out around 90%.
1) Televue - because it allows 496 and 501 nm at 100% transmission and almost flat towards the violet and red spectrum.
2) Astronomik - 496 just below 97% and 501 99%
3) Lumicon - 496 at 99% but clips 501 around 90%

I have the Orion Ultra Block and DGM NPB (Nebula) filters.
The graphs for these two are similiar to a couple of the OIII filters

So, anyone want to take on the question of which would be better for M-97, the Owl Nebula ?




For the Owl, a 'true' OIII filter like the Lumicon or Thousand Oaks would probably be best. The NPB will help as well, but perhaps with not quite as much contrast as the narrower OIII filters. As for Tele Vue's Bandmate OIII, that one is *WAY* too wide (nearly as wide as the NPB), so I would pass on getting that filter. As for "100% transmission", no commonly manufactured filter has that despite whatever passband plots you will see. The most one might expect for most production filters like these is in the high 90's (perhaps 97% or so at one wavelength). In any case, the human eye cannot easily detect a change in brightness of less than 10%, so if an OIII filter has a transmission of around 88% or more at one or both of the OIII lines (and has a Full Width at Half Maximum bandwidth of less than 15 nm but more than 8.5 nm), it should work just fine for visual use. Clear skies to you.


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David Knisely
Postmaster
*****

Reged: 04/19/04

Loc: southeastern Nebraska
Re: OIII Filter Choice new [Re: Paul G]
      #5436194 - 09/23/12 02:04 PM

Quote:

Quote:

This is an often-quoted myth and is definitely *not* true. As I have stated in the past, I have used the OIII in apertures of 50mm and larger with good results. Indeed, one of my favorite views of the North America Nebula comes in my 100mm aperture f/6 refractor at 15x and 25x using the OIII filter, so it definitely does work in smaller scopes. The larger the aperture, the more objects (and detail) will be visible that the OIII will help with, but this does not mean that its use is limited to apertures larger than six inches. It would be nice if Astronomik would not continue to perpetuate this myth. Clear skies to you.




Same here. I have an older (late '90's) Lumicon OIII. With my 105mm f6 refractor and an appropriate eyepiece I get a gorgeous view of the Veil.

David, how do the newer Lumicons compare to an older one like mine? The label on the back of the plastic case says:

<<< PREMIUM
Nebula Line Transmission %
Oxygen - III 496nm 94
Oxygen - III 501nm 95
Hydrogen-Beta 486nm 0.3 >>

The label is pre-printed with the exception of the transmission % numbers at each bandwidth and the word Premium which are hand written in ink. I assume they tested each filter and sold as premium those with the better actual measurements. My Deep Sky is similarly labeled with an additional line for transmsision at 491nm handwritten in.




The newer ones are a little better than those sold in the late 1980's and into the 1990's that still used the laminated protection. The 2" one I have was purchased in the mid 2000's and has fairly good star image quality and no significant secondary passbands outside of the primary one (transmission values of around 94% to 96% depending on which OIII line you are looking at). Clear skies to you.


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Paul G
Post Laureate
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Reged: 05/08/03

Loc: Freedonia
Re: OIII Filter Choice new [Re: David Knisely]
      #5436811 - 09/23/12 07:24 PM

Quote:

Quote:

Quote:

This is an often-quoted myth and is definitely *not* true. As I have stated in the past, I have used the OIII in apertures of 50mm and larger with good results. Indeed, one of my favorite views of the North America Nebula comes in my 100mm aperture f/6 refractor at 15x and 25x using the OIII filter, so it definitely does work in smaller scopes. The larger the aperture, the more objects (and detail) will be visible that the OIII will help with, but this does not mean that its use is limited to apertures larger than six inches. It would be nice if Astronomik would not continue to perpetuate this myth. Clear skies to you.




Same here. I have an older (late '90's) Lumicon OIII. With my 105mm f6 refractor and an appropriate eyepiece I get a gorgeous view of the Veil.

David, how do the newer Lumicons compare to an older one like mine? The label on the back of the plastic case says:

<<< PREMIUM
Nebula Line Transmission %
Oxygen - III 496nm 94
Oxygen - III 501nm 95
Hydrogen-Beta 486nm 0.3 >>

The label is pre-printed with the exception of the transmission % numbers at each bandwidth and the word Premium which are hand written in ink. I assume they tested each filter and sold as premium those with the better actual measurements. My Deep Sky is similarly labeled with an additional line for transmsision at 491nm handwritten in.




The newer ones are a little better than those sold in the late 1980's and into the 1990's that still used the laminated protection. The 2" one I have was purchased in the mid 2000's and has fairly good star image quality and no significant secondary passbands outside of the primary one (transmission values of around 94% to 96% depending on which OIII line you are looking at). Clear skies to you.




Thx.


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rick-SeMI
sage


Reged: 01/08/11

Loc: Michigan - USA
Re: OIII Filter Choice new [Re: David Knisely]
      #5436929 - 09/23/12 08:32 PM

Quote:


For the Owl, a 'true' OIII filter like the Lumicon or Thousand Oaks would probably be best. The NPB will help as well, but perhaps with not quite as much contrast as the narrower OIII filters. As for Tele Vue's Bandmate OIII, that one is *WAY* too wide (nearly as wide as the NPB), so I would pass on getting that filter. As for "100% transmission", no commonly manufactured filter has that despite whatever passband plots you will see. The most one might expect for most production filters like these is in the high 90's (perhaps 97% or so at one wavelength). In any case, the human eye cannot easily detect a change in brightness of less than 10%, so if an OIII filter has a transmission of around 88% or more at one or both of the OIII lines (and has a Full Width at Half Maximum bandwidth of less than 15 nm but more than 8.5 nm), it should work just fine for visual use. Clear skies to you.




David,
I think I am finally catching on!
Bandpass means alot also
I appreciate the info as you have had practical and in the field experience with several filters.
But, can you give me a quick definition of FWHM ?
Does it have something to do with the 496 nm and 501 nm OIII lines? Which have a difference of 5 nm.
I am confused about the 8.5 nm and 15 nm wavelength positions.

Thanks


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David Knisely
Postmaster
*****

Reged: 04/19/04

Loc: southeastern Nebraska
Re: OIII Filter Choice new [Re: rick-SeMI]
      #5437351 - 09/24/12 01:51 AM Attachment (13 downloads)

Quote:

Quote:


For the Owl, a 'true' OIII filter like the Lumicon or Thousand Oaks would probably be best. The NPB will help as well, but perhaps with not quite as much contrast as the narrower OIII filters. As for Tele Vue's Bandmate OIII, that one is *WAY* too wide (nearly as wide as the NPB), so I would pass on getting that filter. As for "100% transmission", no commonly manufactured filter has that despite whatever passband plots you will see. The most one might expect for most production filters like these is in the high 90's (perhaps 97% or so at one wavelength). In any case, the human eye cannot easily detect a change in brightness of less than 10%, so if an OIII filter has a transmission of around 88% or more at one or both of the OIII lines (and has a Full Width at Half Maximum bandwidth of less than 15 nm but more than 8.5 nm), it should work just fine for visual use. Clear skies to you.




David,
I think I am finally catching on!
Bandpass means alot also
I appreciate the info as you have had practical and in the field experience with several filters.
But, can you give me a quick definition of FWHM ?
Does it have something to do with the 496 nm and 501 nm OIII lines? Which have a difference of 5 nm.
I am confused about the 8.5 nm and 15 nm wavelength positions.

Thanks




FWHM is the full width of the filter at half of its maximum transmission level. Most narrow-band nebula filters have FWHM values in the 23 nm to 28 nm range, while good OIII line filters will have FWHM values of between 8.5 nm and about 15 nm. Generally, the filter passband of an OIII filter will be centered at a point in the visual spectrum that is roughly halfway between the 495.9 and 500.7 nm wavelengths with a peak transmission at that point. There is some slight fall-off in transmission away from that peak transmission point, but most line filters have more than 88% transmission at the two OIII lines, so there is little to worry about there. The Baader OIII is a little on the narrow side (8.5 nm FWHM passband width), as the 495.9 nm OIII line is transmitted at only between 35% and 50%, while the other line comes through at over 90%. However, typically, the 495.9 nm OIII line is weaker than the 500.7 nm line, so the Baader filter still works fairly well. Clear skies to you.


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rick-SeMI
sage


Reged: 01/08/11

Loc: Michigan - USA
Re: OIII Filter Choice new [Re: David Knisely]
      #5437935 - 09/24/12 11:49 AM

Quote:


FWHM is the full width of the filter at half of its maximum transmission level. Most narrow-band nebula filters have FWHM values in the 23 nm to 28 nm range, while good OIII line filters will have FWHM values of between 8.5 nm and about 15 nm. Generally, the filter passband of an OIII filter will be centered at a point in the visual spectrum that is roughly halfway between the 495.9 and 500.7 nm wavelengths with a peak transmission at that point. There is some slight fall-off in transmission away from that peak transmission point, but most line filters have more than 88% transmission at the two OIII lines, so there is little to worry about there. The Baader OIII is a little on the narrow side (8.5 nm FWHM passband width), as the 495.9 nm OIII line is transmitted at only between 35% and 50%, while the other line comes through at over 90%. However, typically, the 495.9 nm OIII line is weaker than the 500.7 nm line, so the Baader filter still works fairly well. Clear skies to you.




David,
Thank You.
Excellant explanation and graphic.
I believe I now understand OIII filters much much better from when this thread was started.
These light filters act much the same as SSB and CW filters
Of course with these filters, in the newer rigs, you can vary them at will.
Wonder when the astro filters will become tunable, such as those in a few of the solar scopes ?

TNX
73, Rick - N8XI


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Starman1
Vendor (EyepiecesEtc.com)
*****

Reged: 06/24/03

Loc: Los Angeles
Re: OIII Filter Choice new [Re: rick-SeMI]
      #5438078 - 09/24/12 01:14 PM

One further note: the transmission bandwidth moves in the spectrum as the angle of light incidence changes. The light transmission FWHM figures are for light entering the filter perpendicular to the glass. The bottom and top wavelengths change slightly with small angle changes.
So if you are looking at an object 1 degree wide, the edges of the object do not see exactly the same "window" of wavelengths the center of the object does.
So:
--to examine details, bring the target to the center of the field

Some very inexpensive filters' housings can result in slight tilts in the glass in the housing. That will impact the bandpass.

Because these are basically interference filters, off-axis light may see a completely different spectrum of transmission. You can see that will some narrowband filters which appear blue-green when looking straight through, and pink when looking through at an oblique angle.

If you have a scope with a truly wide true field (like 4-5 degrees), this can actually have an impact on what you see in the field in different parts of the field.

This is a logical reason why the bandwidth of a filter has to be wider than the minimum necessary to be sure to transmit the desired wavelength everywhere in the field.
Otherwise, a 15nm bandpass could transmit H-Beta, and both O-III lines. But, most narrowband filters have bandpasses more like 25nm to be sure slight off-axis views won't get "clipped".


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Scanning4Comets
Markus
*****

Reged: 12/26/04

Loc: Ontario, Canada
Re: OIII Filter Choice new [Re: Starman1]
      #5650382 - 01/29/13 01:54 PM

After reflecting on this subject and owning the Celestron, (Baader OIII), and Lumicon OIII filters, I have come to the conclusion that the Lumicon is the way to go for the OIII filter of choice.

The Celestron / Baader OIII is indeed too dark at 8.5nm.

Cheers,


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photiost
scholastic sledgehammer
*****

Reged: 12/14/06

Loc: Montreal, Canada
Re: OIII Filter Choice new [Re: David Knisely]
      #5657409 - 02/01/13 11:51 PM

Quote:



Here is a site that has some of the current OIII filters transmission curves:

http://www.astroamateur.de/filter/oiii.html

I still like the Lumicon OIII (if you can get one), but the DGM Optics OIII or Thousand Oaks OIII are pretty good as well. Clear skies to you.




I recently got the Burgess Optical (2in) OII filter as part of a deal. The previous owner could not tell me more than he bought it from Burgess about 4 yrs ago.

Any comments/info on this filter is appreciated.
.


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Scanning4Comets
Markus
*****

Reged: 12/26/04

Loc: Ontario, Canada
Re: OIII Filter Choice new [Re: photiost]
      #5680603 - 02/15/13 02:40 AM

My comment two above will now seem somewhat hypocritical because I just purchased yet "another" O-III filter like my last one. My last one was a Celestron and this one is a Baader O-III.

I wanted to try the Baader to see how much alike they really are! There was also a DGM O-III I just missed out on as well. David Knisely: What is the DGM O-III like?

Cheers,


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Ava
sage


Reged: 11/30/11

Loc: Sweden
Re: OIII Filter Choice new [Re: Scanning4Comets]
      #5680672 - 02/15/13 04:32 AM

I have the DGM O-III filter, bought new around 6 months ago. Unfortunately skies have been pretty bad since october basically so I have not used it a lot under the stars. It does give good sharp views, it is certainly a lot narrower than my Astronomik UHC (that one is rather wide) and hightens contarast well for some objects. If I remember correctly, it should be a few nm wider than the Lumicon O-III (around 14-15nm).

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David Knisely
Postmaster
*****

Reged: 04/19/04

Loc: southeastern Nebraska
Re: OIII Filter Choice new [Re: Scanning4Comets]
      #5681562 - 02/15/13 01:52 PM

Quote:

My comment two above will now seem somewhat hypocritical because I just purchased yet "another" O-III filter like my last one. My last one was a Celestron and this one is a Baader O-III.

I wanted to try the Baader to see how much alike they really are! There was also a DGM O-III I just missed out on as well. David Knisely: What is the DGM O-III like?

Cheers,




The one I got for review here on Cloudynights is actually a tad wider than my Lumicon OIII:

CN REPORTS: DGM Optics OIII Filter

Otherwise, it works fairly well. Clear skies to you.


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Starman1
Vendor (EyepiecesEtc.com)
*****

Reged: 06/24/03

Loc: Los Angeles
Re: OIII Filter Choice new [Re: David Knisely]
      #5682052 - 02/15/13 05:48 PM

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.


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Scanning4Comets
Markus
*****

Reged: 12/26/04

Loc: Ontario, Canada
Re: OIII Filter Choice new [Re: Starman1]
      #5682180 - 02/15/13 07:05 PM

What about this filter ? :

Omega O-III Nebular filter # 144918


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