Nebula filters

[Sconesbie]

So last night I found Eta Carinae. No drama. It was a bit faint through my 10" dob. Mind you I was in my backyard with quarter moon and street lights and house lights. I put a moon filter on the eyepiece but all it did was brought out the colours in the stars a bit.

Anyway, my question is what is a good "budget" Nebula filter? I've looked online and have found OIIII and Nebula plus some other types and am confused. A lot of them are over $300. Is that normal?

I only really want to see if I can bring out more detail in nebulas but if I can be "sold" on why I need other ones, I'll save up and invest in those too.

Any help is appreciated.


Regards
Scott

[pgc hunter]

Certainly do not use a moon filter for looking at nebulae!

From my experience, if you are under light pollution, the Eta Carina nebula will not "smack you in the face" like the Orion Nebula as it has a lower surface brightness, i.e. its light is spread out over a larger area and it therefore appears more "dull" at the eyepiece.

Nebulae filters do enhance the appearance of the nebula quite significantly as they block the spectrum where most artificial lighting operates. I would start of with a UHC, or a DGM NPB, these are good all-round nebulae filters. The OIII is a narrower bandpass than the UHC, only letting in the oxygen lines present in planetary nebulae and many emission nebulae. This will make planetaries and some emission nebulae appear with higher contrast than with a UHC, but significantly darkens the background star field compared to the UHC. Its main use is to identify tiny and faint planetaries.

These filters come in 1.25" and 2". The 1.25" versions are 150 bucks at Bintel, the 2" ones sell for 300. Which one you need depends on the barrel diameter of your eyepieces. You can also look through Icetrade, filters often come up for sale, or place a wanted ad if you want to save some coin.

cheers

[gaseous]

Hi Scott,

I've got a DGM NPB filter which works really well on nebulae - I think it cost about $150 USD for a 2", and tends to give a warmer tone to proceedings. Eta Carina will present the star as an intense vermilion colour, whereas OIII filters will give everything a greenish cast which doesn't really appeal to me. DGM NPB filters will also allow in some of the H-alpha wavelength (as well as OIII and H-beta), which may account for the warmer tone, and they've got a pretty good reputation as a narrowband filter. I've also used an Optolong CLS (city light suppression) filter, which while not as "narrowband" as an OIII filter provides a "similar" effect for less money. I was viewing Eta Carina at a dark(ish) site on the weekend and all 3 of these filters all made a huge difference. When doing your research you should try to track down the passband graph for each filter which shows the spread of light being let through - the narrower the better. (although the darker the image will be). I haven't tried the UHC filter that pgc hunter refers to, but I know there are a few reviews/comparisons floating around the net - a chap called David Knisley has done several reports which are very informative. I started with a CLS filter which cost less than $150 for a 2", which might be a decent starting point - generally the more "narrow" the bandpass, the more expensive they tend to get, from what I discovered. Others may have different ideas.

[Zubenel]

I love my Astronomik UHC Filter.It's the ducks guts in my 10"F5. The detail it brings out in the nebula is crazy. Pair it with a widefield eyepiece and WOW:eyepop:

[Benjamin]

Me too! These narrowband filters also operate better at certain exit pupils so when considering 1.25" or 2" keep that in mind: many longer focal length (bigger exit pupil) eyepieces have a 2" diameter and you can always use a 2" filter with a 1.25" eyepiece (given the correct adapter) but not the other way around. I have a 2" Thousand Oaks O-III and H-Beta as well. Both seem to me to be much more useful under darker skies.

[raymo]

If you go to the DGM website you can buy cosmetic seconds at greatly reduced prices; bargain!!!!!
raymo