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UHC or OIII Filter

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#1 Ptarmigan

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Posted 08 August 2014 - 08:10 PM

I am thinking about either getting a UHC or OIII filter. Which filter is better for a light polluted urban sky? Lumicon says OIII filter is better for light polluted sky.



#2 Starman1

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Posted 08 August 2014 - 08:28 PM

Depends.  it isn't a matter of light pollution--it's a matteer of the light emitted by the nebulae.

 

A narrowband reveals both hydrogen-Beta and Oxygen-III transmission,  The contrast enhancement is excellent, and the size of the nebula is likely to be largest. (examples: M42, M8)

Some nebulae emit a lot more enegy in the Oxygen-III lines, and these will be most greatly enhanced by an O-III filter. (examples: Thor's Helmet, The Veil Nebula).

Some nebulae emit almost entire Hydrogen emission and these are helped by an H-Beta filter (example: IC434 behind the Horsehead).

 

If you get only one (or your first one), get a narrowband.  You will be pleased at what you see.  Others will be along shortly to recommend brands, but look for narrow bandwidth and >90% transmission at 486nm (Hb) 496nm (O-III) and 501nm (O-III) wavelengths.

 

If you get a second filter, and O-III is excellent.  While a narrowband filter does well by all nebulae (except reflection nebulae and dark nebulae, which are helped by darker skies), an O-III can provide a stunning view of those objects best suited to an O-III.  I'm sure someone will be along with a link to his guide to nebulae, too.



#3 Jon Isaacs

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Posted 08 August 2014 - 08:31 PM

I am thinking about either getting a UHC or OIII filter. Which filter is better for a light polluted urban sky? Lumicon says OIII filter is better for light polluted sky.

 

It's a tough call.  For the objects that are primarily in the O-III, the O-III will be better for urban skies because it allows the least amount of background light because it has the narrowest band pass. But eventually you will want both and IMHO, it is better to make your filter choices based on dark sky performance rather than urban backyard viewing because while filters are helpful from an urban backyard, it's still a losing battle.. such objects are much better seen when the skies are dark. And from a dark site, the versatility of the UHC filter is greater.. 

 

Also, I recommend buying 2 inch filters, such filters are most useful at lower magnifications, with their larger, brighter exit pupils. 2 inch filters can easily be used with 1.25 inch eyepieces but the 1.25 inch filters cannot be used with 2 inch eyepieces..

 

Jon 



#4 kfiscus

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Posted 08 August 2014 - 11:57 PM

I'd recommend the Lumicon O-III (2" can be bought used for $150) and the DGM NPB (2" can be bought new for $150). They are superb and worth every penny. I had to wait quite a while to grab a used Luminary but it saved me $90!

I converted to 2" filters so that I could use a filter slide. Filters are too useful, fragile, and expensive to have and under-utilize by threading and unthreading them in the dark.

#5 kfiscus

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Posted 08 August 2014 - 11:58 PM

I'd recommend the Lumicon O-III (2" can be bought used for $150) and the DGM NPB (2" can be bought new for $150). They are superb and worth every penny. I had to wait quite a while to grab a used Lumicon but it saved me $90!

I converted to 2" filters so that I could use a filter slide. Filters are too useful, fragile, and expensive to have and under-utilize by threading and unthreading them in the dark.

Edited by kfiscus, 09 August 2014 - 12:04 AM.


#6 kfiscus

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Posted 08 August 2014 - 11:58 PM

You should Google DGM (the company) and NPB (Narrow-Pass Band). I learned of it here on CN from the resident filter guru David Knisely.

Edited by kfiscus, 09 August 2014 - 12:07 AM.


#7 kfiscus

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Posted 09 August 2014 - 12:10 AM

Sorry for double post above. The new format is much harder to edit and I can't find a delete post option.

#8 David Knisely

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Posted 09 August 2014 - 12:21 AM

I am thinking about either getting a UHC or OIII filter. Which filter is better for a light polluted urban sky? Lumicon says OIII filter is better for light polluted sky.

 

 

Buy both.  There are some objects that respond better to an OIII filter than the Lumicon UHC (and some where the skyglow is most supressed with the OIII).  However, other objects have either a "balance" of OIII and H-Beta or more H-Beta emission.  For them, I would suggest a good narrowband nebula filter like the DGM Optics NPB (my favorite), Lumicon UHC, Thousand Oaks Narrowband LP-2, or Orion Ultrablock.  The narrowband filter tends to work on most emission nebulae, while the OIII may work on many, but not quite as many as the narrowband nebula filter works on.  Thus, having a good narrow-band nebula filter as well as a good Oxygen III line filter is a good way to go.  I might suggest the following two articles for the details on filters:

 

http://www.prairieas...w-band-filters/

 

http://www.prairieas...common-nebulae/

 

Clear skies to you.


Edited by David Knisely, 09 August 2014 - 12:22 AM.



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