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Visual filters - Oiii, UHC, Hb

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18 replies to this topic

#1 B l a k S t a r

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Posted 04 February 2019 - 05:19 PM

So I've decided to go for it and purchase filter sets for my 100mm binoscope and 101mm refractor. I have a 2" UHC filter that I've tried naked eye, holding up to one eye using my binos (8x42s and 25x100s) and quite frankly had no luck. Not even the NA nebula. I think I'll have better luck with both eyes engaged and more trips to darker skies. 

 

So, I'll probably sell the 2" UHC and get a pair of 1.25". Also, I will get a pair of Oiii. My question now is, should I bother with Hb?  RASC handbook says there are very few targets for Hb and lists only the horse head nebula, still ... 

 

 



#2 pkrallis

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Posted 04 February 2019 - 05:33 PM

The effect of filters in visual observing is significantly improved as aperture increases.


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#3 havasman

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Posted 04 February 2019 - 06:07 PM

I would hold off on the H-Beta until the others prove themselves. In fact, I'd try either UHC or O-III before jumping completely in and go for proof of concept first.

I recently tried Lumicon UHC's mounted over the objectives of my 10x50's and it was more underwhelming than I'd hoped. I hope you have better luck.


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#4 AxelB

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Posted 04 February 2019 - 07:49 PM

For observations with at least 2.5mm of exit pupil, the UHC will be your most useful filter (that would mean a 17.5mm eyepiece on f7 refractors). Bigger exit pupil is even better.

With the Oiii it’s better to have at least 3mm of exit pupil (so even less magnification). These are rules of thumbs, there are some bright planetary nebullas on which we can use more magnification.

#5 Jon Isaacs

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Posted 04 February 2019 - 08:43 PM

So I've decided to go for it and purchase filter sets for my 100mm binoscope and 101mm refractor. I have a 2" UHC filter that I've tried naked eye, holding up to one eye using my binos (8x42s and 25x100s) and quite frankly had no luck. Not even the NA nebula. I think I'll have better luck with both eyes engaged and more trips to darker skies. 

 

So, I'll probably sell the 2" UHC and get a pair of 1.25". Also, I will get a pair of Oiii. My question now is, should I bother with Hb?  RASC handbook says there are very few targets for Hb and lists only the horse head nebula, still ... 

 

Brian:

 

Filters are effective , very effective.  But they can't work miracles..  Nearly so though .  From my red zone back yard , I can detect the Veil with an O-3 in an 80 mm.  Never seen the NA from my urban backyard , it takes darker skies even with filters .

 

- Filters are effective with small scopes and large scopes , exit pupil is the key.  Larger exit pupils in general .

 

- I imagine you binocular telescope uses standard eyepieces but how about your 42 mm's ? How do you plan to use the filters there ? 

 

- H-Beta is the same least used of the three . For binos. . The California Nebula is nice .

 

Jon



#6 B l a k S t a r

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Posted 04 February 2019 - 10:34 PM

Seems prudent to hold off on the Hb filters. As far as aperture is concerned I'll see what I get, literally. There's always the club scope, an 18" plus a new 14".  I will have to construct holders to fit over the smaller binoculars eyepieces. 

 

I tried an Oiii on my 101mm refractor last winter on M42 and was pleasantly surprised at the green cloud popping out. The binoscope is 100mm so I consider it to be +40% or the equivalent of a ~140mm aperture, plus the advantages of both eyes active. 



#7 Mike W.

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Posted 05 February 2019 - 08:16 AM

This may help you in your endeavor, knowing how to figure the exit pupil if you don't already know is to devide the eyepiece folcal length by the scopes focal ratio.

 

clipped from the net:

 

To calculate the exit pupil of a telescope, divide the focal length of the eyepiece in millimeters by the focal ratio of the scope. For example, a 25mm eyepiece used in an f/5 scope delivers an exit pupil of 25/5=5mm, while a 35mm eyepiece in the same scope delivers an exit pupil of 35/5=7mm.

 

In my scope I figure right around 100X for DSO hunting and viewing with filters.

 

I have a favorite eyepiece for that, it's a bit below 100X but they don't make a 12mm 100° eyepiece so I settled on 13mm and have 2.7mm exit pupil.


Edited by Mike W., 05 February 2019 - 08:20 AM.


#8 Mike W.

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Posted 05 February 2019 - 08:37 AM

Some find it easier on their eye's to be around a 5mm exit pupil for fainter DSO's, in my scope that's pretty close to a 20mm eyepiece, then I got a Pan 35 for those really wide DSO's, and at 34X

 

I chose the Pan vs Nagler due to weight constants.



#9 B l a k S t a r

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Posted 05 February 2019 - 03:40 PM

This may help you in your endeavor, knowing how to figure the exit pupil if you don't already know is to devide the eyepiece folcal length by the scopes focal ratio.

 

clipped from the net:

 

To calculate the exit pupil of a telescope, divide the focal length of the eyepiece in millimeters by the focal ratio of the scope. For example, a 25mm eyepiece used in an f/5 scope delivers an exit pupil of 25/5=5mm, while a 35mm eyepiece in the same scope delivers an exit pupil of 35/5=7mm.

 

In my scope I figure right around 100X for DSO hunting and viewing with filters.

 

I have a favorite eyepiece for that, it's a bit below 100X but they don't make a 12mm 100° eyepiece so I settled on 13mm and have 2.7mm exit pupil.

Every once in a while I tell myself I should commit the pupil diameter formula to memory in addition to the magnification. It's really not a hard formula to rough out in my head. 

 

My refractor is 550 fl at 101 objective for a ~5.5 fr

So my 25 mm plossl pupil is 4.5 mm dia 

 

My binoscope is 550 fl at 100 for the same 5.5 fr

The 12.5mm eyepiece pupil is 2.3mm

The 9mm eyepiece puphill is .6 mm dia. 

 

Now I've read here on CN a bino equivalency for ocular diameter is +40%.  If I apply that formula logic to pupil diameter how will the CN community respond? I'd love to know I could achieve a maximum equivalent pupil of not 7, but nearly 10 mm dialation without taking the red pill. 

 

Kaboom!!

 

edit: corrected 5.5 fl to fr


Edited by B l a k S t a r, 05 February 2019 - 04:38 PM.

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#10 AxelB

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Posted 05 February 2019 - 06:13 PM

Every once in a while I tell myself I should commit the pupil diameter formula to memory in addition to the magnification. It's really not a hard formula to rough out in my head.

My refractor is 550 fl at 101 objective for a ~5.5 fr
So my 25 mm plossl pupil is 4.5 mm dia

My binoscope is 550 fl at 100 for the same 5.5 fr
The 12.5mm eyepiece pupil is 2.3mm
The 9mm eyepiece puphill is .6 mm dia.

Now I've read here on CN a bino equivalency for ocular diameter is +40%. If I apply that formula logic to pupil diameter how will the CN community respond? I'd love to know I could achieve a maximum equivalent pupil of not 7, but nearly 10 mm dialation without taking the red pill.

Kaboom!!

edit: corrected 5.5 fl to fr


Your 12.5mm eyepiece with an f5.5 instrument could be used with an uhc filter, it’s close enough to my rule of thumbs. Still, you would probably get more interesting results with longer eyepieces.

#11 Akol47

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Posted 09 February 2019 - 02:18 PM

If I'm reading this correctly filters are better suited for faster scopes with larger EPs? I've been considering either an UHC or LP. I know some are one in the same but it seems more reasonable to me to find out if my scopes would benefit from a filter. Do any of the LP or UHC or OIII filters work for visual?



#12 Mike W.

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Posted 09 February 2019 - 03:27 PM

If I'm reading this correctly filters are better suited for faster scopes with larger EPs? I've been considering either an UHC or LP. I know some are one in the same but it seems more reasonable to me to find out if my scopes would benefit from a filter. Do any of the LP or UHC or OIII filters work for visual?

For your sct or refracter you might benefit with either a UHC or O-III,

 

Is the LP you're asking about, is that the Thousand Oak's LP-1 or -2?

 

Or are you referring to "Light Pollution" filter's?



#13 Akol47

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Posted 09 February 2019 - 03:30 PM

Would be a light pollution filter but I have read that some of the UHC filters are essentially light pollution filters



#14 Akol47

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Posted 09 February 2019 - 03:33 PM

Is there a specific brand of UHC you would recommend, noting that I'm only using 1.25 EPs



#15 Mike W.

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Posted 09 February 2019 - 03:47 PM

Would be a light pollution filter but I have read that some of the UHC filters are essentially light pollution filters

In a way yes and no, to much of a broadband filter,,,,,

 

With the smaller aperture of your equipment in your signature, the more the reason for line filter (O-III), or UHC  (Narrow Band) 

 

To help you understand, yes you want to block light pollution but there is so much now from full spectrum LED lighting that you might as well target the emission lines of the DSO's and block everything else out, yes it darkens the view a lot and that's also the reason for dark site locations, the more your eye's get dark dark adapted then the faint light of the DSO can be seen.

 

When you block all the other light out except the DSO's emission light, it's not very much light to work with.

 

Helpful?

 

Might try viewing hoods, but every time your head leaves it's cover you'll have to wait for them to adapt dark again.



#16 Akol47

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Posted 09 February 2019 - 04:08 PM

Very helpful, again I've only been considering them but your reasoning makes sense



#17 Starman1

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Posted 09 February 2019 - 04:56 PM

If I'm reading this correctly filters are better suited for faster scopes with larger EPs? I've been considering either an UHC or LP. I know some are one in the same but it seems more reasonable to me to find out if my scopes would benefit from a filter. Do any of the LP or UHC or OIII filters work for visual?

Uh, no, they aren't only for fast scopes and large eyepieces.

They work by restricting the bandwidth transmitted to mostly the nebula emission lines and blocking the rest.

This increases contrast, making the nebulae more visible.

They work for all f/ratios.

However, as the field dims with increased magnification, the contrast enhancement diminishes, so they are typically used at low powers, under, say, 10x/inch of aperture.

 

Yes, your scopes would benefit from the use of nebula filters.

 

Just about all of them were originally intended for visual use.

 

There are a few basic visual types:

 

--broadband (aka LPR).  Transmit all the light except for a swath in the yellow-orange.  These were designed back when those wavelengths were where most light pollution was.

Today's light pollution spans nearly the entire spectrum, so the effectiveness of these filters, which is modest at best, is better at sites with already dark skies.

 

--narrowband (aka UHC).  Good visual ones transmit the 486.1nm line of H-ß, the 495.9nm line of O-III and the main O-III line at 500.7nm and almost nothing else.

Bandwidths of 21-26nm are best, with transmission at all 3 lines over 90%.  Wider filters yield less contrast enhancement.

These work well on all forms of emission nebulae, so this is the 'universal' nebulae filter.

 

--line filters (aka O-III or H-ß).  For O-III only filters, a 11-15nm bandwidth with both O-III lines >90% transmission is best.  For H-ß filters only, a 9-12nm bandwidth with transmission of >90%.

O-III filters work best on planetary nebulae, supernova remnants, and Wolf-Rayet excitation nebulae.  H-ß filters work best on large faint (because you need maximum contrast) hydrogen emission nebulae.

Line filters yield the maximum contrast for the types of objects viewed.

 

Photographic O-III filters are narrower, and only pick up the 500.7nm spectral line.  This yields more contrast, but requires longer exposure.  Not best for visual.

Photographic H-ß filters don't exist.  All hydrogen nebulae emit more energy at H-α in the deep red, but because we don't see that wavelength much at night, we use the H-ß in the blue.  Imagers all use H-α.

Photographic Narrowband filters don't exist because imagers prefer to expose specific wavelengths and combine images.  A UHC-type would yield too little contrast, and they don't want the H-ß anyway.

Photographic use of broadband filters is possible, but the effectiveness of the filters has diminished, so this is becoming far less popular.


Edited by Starman1, 09 February 2019 - 04:57 PM.

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#18 B l a k S t a r

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Posted 09 February 2019 - 07:47 PM

I was all set to acquire a pair of UHC and a pair of Oiii filters for binoscope and telescope visual viewing. I ended up purchasing just the UHC pair because they pass Hb and Oiii while the Oiii pass no Hb. Thanks to Glenn LeDrew for the education and clarification.  More available now for one more 2" dia UHC to fix to the front of my 8x42s and 10x50s. The 1.25" dia pair will thread onto eyepieces on the binoscope. 

 

So overall a good solution that suits me just fine. Oiii without Hb? - paltry eye candy!

 

Happy viewing ahead. 


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#19 Akol47

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Posted 10 February 2019 - 03:24 PM

Great info starman1, will definitely consider acquiring at least one filter.




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