Filter for the Horsehead Nebula

[astronut]

I was recommended this Filter (http://cgi.ebay.com/Optical-Filter-Astronomy-Na-Hg-Skylight-Reject-48mm_W0QQitemZ350276918466QQcmdZVie wItemQQptZLH_DefaultDomain_0?hash=i tem518e219cc2) to help view the Horse head Nebula.
I would like the opinion of the filter experts on I.I.S about this.
Thanks, John. :)

[JethroB76]

I think HBeta is what you're after, at the omega store in your link there is a HB/OIII listed but I dont know how much of compromised that is:shrug:

[astro744]

H-Beta for sure. Look at http://www.lumicon.com/astronomy-accessories.php?cid=1&cn=Filters

Note the O-III misses the mark completely. The UHC combines both H-Beta and O-III but you really need the narrower bandwidth of the H-Beta to have a chance at the Horsehead. You also need a bit of aperture (10-12") or a very dark sky in which case a 6" may show it but 8" and over would be better.

You should also use an eyepiece to give you a large exit pupil (low power) but you can try mid powers too.

Everything will look fairly dark, but the horsehead will look just that little bit darker. Take note of the field stars to ensure you are looking at the correct location and get your eyes well dark adapted. Turn off any notebooks (should be the norm anyway if you want to see faint objects).

[ngcles]

Hi John,

The filter you are contemplating will give, at best, a mild contrast-boost on the Horsehead Nebula (IC 434) in suburban areas. It is designed to block the emission from certain street lights such as the Mercury vapour and low-pressure Sodium lights. Other than that it has very wide pass-bands . It will be of very limited use visually on nebulae -- a quite mild contrast boost in suburban areas where there is quite a bit of this sort of lighting. It is primarily an imaging filter, rather than visual use.

As Jethro has already said, you need either a (1) "UHC" type filter -- a narrowband filter that allows H-Beta and OIII (doubly ionised Oxygen) light through. This will give a good contrast gain on nearly all emission nebulae.

Even better for this particular object and just a few others (2) a Hydrogen-Beta filter, that has a very, very narrow pass-band centred over 486nm giving a somewhat higher contrast boost on nebulae like the Horsehead where there is little emission other than via the several Hydrogen lines.

H-Beta filters, because they block so much light are really only usable on good-sized telescopes. As to what the definition of "good-sized" is varies depending on who you speak to. Personally I don't think it has any great benefit with telescopes smaller than 10" aperture, but opinion varies. Smaller than 10", I'd personally be inclined to go with the UHC type that has a wider band-pass.

Most H-Beta filters are designed to be used at a magnification providing an approximately 5mm exit-pupil. That's not to say they won't work at other magnifications/exit pupils, but that's where they work best.

There are seveal leading manufacturers, I'd be inclined to stick with those with a proven track-record or "your mileage may vary ..."


Best,

Les D

[erick]

My H-Beta is in the mail. Going after Horsie this year with my coming re-built 12"! :thumbsup:

[astronut]

Thanks Guys,
I appreciate all the great advice.
Now all I need is a clear sky!!:lol:

[erick]

Well, it got lost in the mail for a few weeks, but I have it now. A nice red Thousand Oaks H-beta filter. I'm ready!

[PhilW]

Three further comments about this:

1) Les's 5mm exit pupil is a key tip for this object. So in an F/5 scope, that means an eyepiece around 25mm focal length.

2) I think you'll need a very transparent night to see it in a 12" scope (although it is definitely possible). I found it a fairly marginal object in my 14"; it is now relatively easy in the 20", which is to say we can spot it on any reasonably good night with either H-beta or UHC filter.

3) Make sure you get Zeta Orionis out of the field of view. It is glaring.

Phil

[astronut]

2" Eric? Could you clone it and send it to me?:lol:

[erick]

Yep, 2" - is there any other size for maximum convenience :P


Perhaps I can start a little hire business? :D

[erick]

Definitely observed the Horsehead Nebula about 3 hours ago at Snake Valley Camp. :)

12" reflector; 20mm Televue plossl, H-Beta filter. More later.......

[JethroB76]

Well done..did you try it also with the DGM NPB?

[erick]

Sorry, no - but my appetite is whetted now. I'll go after this target again and experiment. All reports that I have read suggest H-Beta is the preferred filter for this target.

[JethroB76]

Yeah, I don't have a Hbeta at the moment but do have a DGM NPB, hence the question.

[erick]

Perhaps I can on Dec new moon weekend?

[JethroB76]

yeah, I'll give it a go again with my NPB and ultrablock filters. Would just be interesting to know what difference there was on the same night between the H-Beta and a UHC type filter on this object.
Have been tossing up buying a H-Beta filter but if I could see the HH well enough with a UHC, I probably wouldn't bother.

Curious also, whether you tried any other f/l EP's? My 20mm nagler I think is the best suited of the EP's I have, as an exit pupil of about 4-5mm is supposedly optimal

[erick]

Alex borrowed my 20mm Plossl to use with his 22 inch f3.6 saying that gives him the exit pupil and field of view that he wants.

I didn't have a 25mm with me. I had 10mm then 19mm, 20mm, 27mm. I started with my 19mm Panoptic but was unsuccessful - but it might have been my eyes were not fully dark-adapted. I swapped to the 20mm plossl and saw the Horsehead through it after several careful minutes work. I didn't then go back to the 19mm Panoptic. The field of view in the 20mm plossl was just perfect. The extra AFOV degrees of the Panoptic would have been wasted.

The 20mm plossl is a 4mm exit pupil in my scope. Next time I will take a 25mm plossl as well - I have a few cheaper ones.

[mental4astro]

Following up on Jethro's question, I too am thinking - Will I see the HH with the UHC? Sure the H Beta will do it, but I'm happy to buy a UHC, but the H-beta too not so keen. :shrug:

[koputai]

An interesting read on this subject:

http://home.ix.netcom.com/~bwilson2/barbarasweb/MEyepiece.htm

Cheers,
Jason.

[Jeeps]

Great link!

Thanks!