What filter do I need

[Shaun Sr]

What filter should I get for deep sky. I have an 8edge HD and a ed80 f100 i have an adaptor 2 to 1.25 for my 2in diagonal so a 2in filter so I can use it for all my eyepieces and they are 17.5 mm down to 8.  OIII?

[Louis D]

For emission nebula, an OIII is the most aggressive and often yields the best view.  The slightly less aggressive UHC types also show the H-Beta line and sometimes include the H-Alpha and SII lines as well.  However, more light pollution is let in due to the wider passbands, decreasing contrast on low surface brightness nebula.
 

OIII passband:

Typical UHC passband including H-alpha and SII:

Other DSOs don't really benefit much from filtration.  Open clusters tend to be "large" and high contrast, so no issues there.  Globular clusters tend to be small and compact and do best with high power (200x+) and at least 6 to 7 inches of aperture to start to resolve them into tiny pinpoints.  Planetary nebula tend to be compact and benefit from high power as well because that reduces the background skyglow.  Galaxies really need dark skies because they emit light across the entire spectrum, so no filter helps to increase contrast with them in light polluted skies.

[Shaun Sr]

so get an oIII?  I deal with lp. But I travel to dark as well

[Louis D]

On 29/07/2020 at 10:04, Shaun Sr said:

so get an oIII?  I deal with lp. But I travel to dark as well

I would start with the OIII and add a UHC as funds become available.  For planets, a generic Moon & Skyglow filter can help increase contrast.  The cheap versions have basically the same passbands as the Baader Neodymium filter, so save your money on that filter and go generic.  The generic OIII filters, however, are not very good compared to the leading brands, so don't skimp on it.

[LukeSkywatcher]

I hope that i have this right:

A UHC filter enhances what is already visible to the naked eye.  An OIII makes objects invisible to the naked eye, visible.

Feel free to correct me if i have this backwards.

I have both. I couldnt decide on one or the other, so i get both. Baader branded.

[Gina]

Filters only make invisible objects visible with long exposure imaging.

[LukeSkywatcher]

9 minutes ago, Gina said:

Filters only make invisible objects visible with long exposure imaging.

Ive seen the Rosette with an OIII filter visually. Im guessing imaging it would bring out more detail, but ive seen it.

[Kev M]

O3 is right in the middle of the visible spectrum so if bright enough objects emitting/reflecting this would be visible to a human eye.

Probably look Green in colour.

 

 

[Louis D]

The Veil nebula is all but invisible in my skies, but easily visible with an OIII filter.  It's simply a matter of increasing the contrast by eliminating non-nebula emitted light from light pollution.

With the Orion nebula, which is quite bright, it simply allows a greater extent of the faint filaments to be seen.

Edited July 30, 2020 by Louis D