Nebula questions

[earth titan]

Couple of questions about nebulas if I may..

Is it worth buying a filter? I have seen reviews for the Skywatcher UHC Filter. Any good? Does it do what it says on the tin?

Also, any tips on best time of year and tips for looking at Orion, Trifid, cone etc. as they all seem to be very low in the sky for the majority of the year in the UK.

[Chris H]

I have the Skywatcher UHC filter and use it with my 10" dob. I've not really been too impressed with its performance, I find it dims the image too much and you may find that is more of a problem with your 6" scope. I'm currently thinking of paying more and getting a Lumicon UHC.

[ollypenrice]

UHC filters have their place, yes. They make certain objects visible even at a dark site where you might expect them to be visible anyway. All filters reduce light but gain by enhancing contrast.

To check the elevation of objects above the horizon the easiest way is to use a computer planetarium into which you can plug your co-ordinates. I use SkyMap Pro, which is fabulous, but others may recommend free packages along the same lines.

Sagittarius etc (Trifid-Lagoon) is always going to be tough in the UK but Orion will be a piece of cake in the winter. We are down at Lat44 here but we are still tempted by the 'tree-skimmers' in the south! I'm all set for a couple of hours imaging on the Antares region when the moon goes. Why make life easy when you can make it difficult???

Olly

[LukeSkywatcher]

So basically nebula filters do not work?

[Chris H]

So basically nebula filters do not work?

They do work but their benefits are often not worth the expense.

[LukeSkywatcher]

Right so................i'll keep my money in my pocket.

[Chris H]

I think that with more aperture a good UHC filter will show nebulosity that would not be seen without it. When I use the UHC to look at M42 more of the nebula is visible but the nebula as a whole is dimmer.

[John]

I have to disagree with this. UHC and OIII filters do work and, on the right objects, make a significant difference on what you can see, especially on planetary nebulae like the Owl and the Veil which are practically invisible in small to medium aperture scopes under normal seeing conditions without a filter. The brands that I have found effective are the Baader UHC-S (for smaller scopes) the TS UHC, the Orion Ultrablock and my current Astronomik OIII which is superb.

So don't write them off - depending on your observing conditions they may just make the difference between seeing and not seeing some objects.

[LukeSkywatcher]

So basically the bigger the apeture the better these filters work.

[zhgutas]

So basically the bigger the apeture the better these filters work.

Based on the working principle of nebular filters, AFAIU this is true at least in some way (mind you this ONLY my understanding, which may be waay wrong).

e.g. if 60mm refractor is not capable of gathering enough particular emission line light to resolve a particular nebular target, I doubt a filter would help, because even filtering out the interfering light, the object would be too dim to see.

Another story then, is looking at the same target with, say an 8" dob where the amount of the particular emission line gathered is enough to be detected by the eye, only it is "washed out" in the presence of all the remaining spectrum, and thus, is not seen/poorly seen due to the lack of contrast. This is where the filter kicks in.

So essentially, you can not filter out the stuff, if it isn't there in the first place (or there is just too little of it).

However, when observing from a really dark site with a suitably sized instrument, a non-filtered view may be much more pleasing to the eye, as there is not too-much "unnecessary" light in the way, and a sufficient aperture gathers enough particular emission line light to make the image more detectable. thus, using nebular filter may be less useful, as compared to less perfect skies imho

Hope that makes some sense

Marius

[moocher]

If you look say at the Veil Neb (Cygnus, Summer constellation) without an O111 filter you can barely see it with the filter it really pops out so i`d say with a reasonable aperture say 8" they do work!!! The larger the scope the better as its all about light grasp...

Alan:D

[John]

So basically the bigger the apeture the better these filters work.

Generally, I'd agree however the Baader UHC-S is effective even with small apertures - I managed to spot the Veil nebula using one with an 80mm F/5 refractor. The Baader OIII however is the opposite - it's band pass width is really narrow so it does need 8" or larger apertures to work well I feel. Thats another thing to bear in mind when considering these things - different brands of UHC or OIII filters have slightly different characteristics which suit some scopes, and observers and not others.