UHC/OIII filters

[Jakstaar17]

Hi Everyone.

I have decided that my next purchase will be a filter to enhance the viewing of nebulae.

If possible, i would like to see the colours of some of the nebulae, and the descriptions of FLO of some of the filters say that you will get near photographic view of Orion's nebulae, ring nebulae and more.

I have a Skywater Skyliner 200p Dob.

Which filter would everyone recommend for use with my scope?

I have had a look at the following page from FLO;

UHC & OIII Visual filters

Thanks very much.

[Ben Ritchie]

I'm not sure what the context is for

you will get near photographic view of Orion's nebulae, ring nebulae and more.

but the general consensus is that you're only likely to see colour in M42, and that's a pale greenish tint. I guess they mean that the improved contrast from these filters may make these objects be 'near photographic', i'm not sure.

The only colour you could see with an [O III] filter is green, as it's purpose is to isolate two nebular emission lines in the green region of the spectrum. The transmission at all other wavelengths should be zero. UHC filters add in Hydrogen-beta line (also in the blue/green) and sometimes H-alpha (in the red, although the eye's relatively insensitive to those wavelengths)

[Ogri]

I'm not sure about the colours, but I think bigger reflectors do show a little (yours may well be up to it). eta: Ben mentioned green and I remember someone else saying they had seen green with something.

Personally I am more than happy with black and white, and like with black and white fine art photography, contrast is essential, and that's where the filters you mention, come in (apart from the variations in light frequency allowed to pass too).

The view of Orion's nebula in black & white in good viewing conditions, is jaw droppingly beautiful, and even if I do get something eventually that will display a little colour, I won't exactly worry about it, hehe.

I would actually start with a Skywatcher Light Pollution Filter, which has very nice mild contrast, which could well suit a lot of viewing conditions, as well as specific targets. This from the advert with FLO:

"Bright, light-polluted skies appear darker, and the contrast between object and sky is improved significantly. This contrast-enhancement effect is particularly apparent on nebulae. Unlike stars, emission nebulae give off light in a very narrow range of wavelengths. The filter allow maximum transmission of the important wavelengths of H-alpha, H-beta and doubly ionized oxygen – the ones most commonly emitted by nebulae. Views of galaxies and star clusters are also enhanced, but to a lesser degree. Also improves contrast on reddish planetary detail." Light Pollution Reduction - Skywatcher Light Pollution Filter

Well I can certainly vouch for that with my ST120 'scope.

As an aside, I don't have light pollution to worry about, the Milky Way is clearly visible to the naked eye where I live, and that said, the LPF has to be one of the best value investments I have made.

The UHC I use, is a Castell (supposedly very similar, and I am very happy with the very noticeable extra contrast), which also works well, and definitely complements the Skywatcher LPF.

I haven't added an OIII yet, but once I get a bigger 'scope with more light grasp (where the heavier contrast will likely be more useful), that will be right on the list after a collimator.

Hope that helps.

[Ben Ritchie]

One further thought, it's worth remembering that filters can only remove light, they can't add it - so they can't make your 'scope see anything more than it otherwise could. They can just make it stand out more by removing light pollution, starlight etc. that distracts from what you're observing.

[Jakstaar17]

Colour isn't much of a problem really.

However, if it makes nebulae much more visible, then that would be great.

From the reviews, some say that the UHC filters help out with light polluted skies. So does a UHC filter not do a similar job to a LPF?

I would prefer to only get one at the moment and if i could use it to enhance galaxies and clusters, as well as nebulae, then brilliant.

If the LPF will enhance all of these then i will go for that one.

With the Pleiades cluster, for example. Would i be able to get any of the gas around it (not expecting colour), as without a filter, it is just the stars (even though it is a spectacular view).

Thanks very much!

[Ben Ritchie]

UHC is effectively an [O III] filter plus Hydrogen beta, so it's the more general purpose of the two filters. However, both are most effective on emission-line nebulae, which emit strongly at H-beta and [O III] (amongst other) wavelengths. They're less effective for stellar sources - clusters, galaxies etc. - as these emit radiation at all wavelengths.

With the Pleiades cluster, for example. Would i be able to get any of the gas around it (not expecting colour), as without a filter, it is just the stars (even though it is a spectacular view).

No - that's a reflection nebula, which as the name suggests is dust reflecting starlight. So it's a broadband source.

[Andrew*]

This should help you out:

http://stargazerslounge.com/primers-tutorials/84192-primer-understanding-choosing-filters-visual-use.html

[Jakstaar17]

Ok then. Could anyone point me to any comparison pictures of using filters and without filters?

So if i would like to use it for nebulae and galaxies to help make out more detail, what would you suggest? Go for the cheaper option of a LPF?

And what do LPF filter compared to UHC filters?

Sorry for all of the questions. Just want to make sure i get the right filter for my needs before i splash the cash.

Thanks again.

[Ogri]

"From the reviews, some say that the UHC filters help out with light polluted skies. So does a UHC filter not do a similar job to a LPF?"

Indeed it does.

The contrast is very noticeably 'heavier' over the LPF though.

As a rough guide, perhaps consider the LPF, the UHC, and the OIII, to be three increasing grades of contrast, from mild to heavy, with the UHC being roughly central.

Each do allow different detail to be observed from what I gather (I can confirm that's definitely the case between the LPF and the UHC anyway).

With your 200p, perhaps start with a UHC, and if you find the contrast a bit too heavy for some things, then pick up a LPF, given its greater light grasp than my ST120?

The more light that's grabbed, the easier it is to scrub some off without too bad an effect (why I have avoided an OIII at the moment, even though soem have had great results with smaller 'scopes).

I got my Castell UHC from here Other Contrast & Deepsky Filters : 365Astronomy: Discovery for every day! and they also do an OIII.

[Ben Ritchie]

And what do LPF filter compared to UHC filters?

Light-pollution filters are effectively the inverse of emission line filters.

Things like [O III] and UHC block all light apart from certain discrete wavelengths corresponding to particular transitions in gaseous nebulae, so the contrast of the targets is improved. Light pollution filters seek to allow all wavelengths apart from certain wavelengths found in street lighting etc., to remove man-made background.

Under perfectly dark skies, a [O III] or UHC filter would still have an effect, whereas a LPR filter would do almost nothing.

[Jakstaar17]

This should help you out:

http://stargazerslounge.com/primers-tutorials/84192-primer-understanding-choosing-filters-visual-use.html

Thanks. I had a read through that and that is how i came to the conclusion that a UHC filter may be best for me as it performed best on the nebulae that i was interested in viewing.

I only have a couple of street light polluting my house and i am in the countryside so i wouldn't say that the skies here are particulary light polluted.

Would it be a good idea to buy a UHC filter now and look for a LPF on the for sale section. Then maybe use them together?

Thanks

[Jakstaar17]

Great. Thanks for the help guys.

I think i will buy the UHC filter now and then try to find a LPF afterwards.

Cheers!

[Ogri]

Ben:"Under perfectly dark skies, a [O III] or UHC filter would still have an effect, whereas a LPR filter would do almost nothing. "

Got to be honest Ben, I find the Skywatcher LPF, makes a terrific difference, even under dark skies (eta:caveat: I do have pretty weird and very sensitive eyes).

PS I think you would have ended up buying the UHC anyway (definitely worth having), and thinking about it, there is a chance that the contrast benefits from a LPF might not be so beneficial in a 200p reflector. Ideally, borrow one to try so you can compare the views between the two. Personally I switch out between the LPF and the UHC quite a bit, depending on what I am looking at, and I think there's maybe a bit of a consensus that the LPF is particularly suited to 'scopes of 6" or under, as it doesn't remove too much light?

In a way, the benefits you will get from a UHC, might be in line with the benefits I get from the LPF?

[Ben Ritchie]

I'd guess that the SW LPF one has quite broad cutouts in transmission, and therefore acts as a quite effective contrast booster too?

[Jakstaar17]

Not sure whether to go for the SW UHC from FLO or the Castell UHC from 365Astromomy.

[Ogri]

I'd guess that the SW LPF one has quite broad cutouts in transmission, and therefore acts as a quite effective contrast booster too?

Yes I love the contrast with it tbh, and use it more than the UHC with viewing conditions as they are at present.

Clear winter skies though, that might be reversed?

eta: It seems to tolerate poor viewing better than the UHC, with the light grasp of the ST120 (I get flaring with the UHC which makes you think something serious has gone wrong with the 'scope or the EP ). In reasonably good viewing conditions, it is very impressive though.

PS. I bought 2" versions of each, and fit them into the nose of the diagonal.

[Jakstaar17]

So Ogri, would you recommend the Castell UHC then? I will buy it now if so

[Ogri]

So Ogri, would you recommend the Castell UHC then? I will buy it now if so

Well I like it enough to have a mind to get their OIII when I get a bigger 'scope. No complaints at all (admittedly viewing conditions haven't been exactly great since I got either of them, to fully put them through their paces, but the selective contrast I find to be superb with them and worth having just for that).

I have come across reports that they are somewhat the same filter off the same production lines as much more expensive ones, but bought direct and rebranded by/for a guy in Austria?

[Jakstaar17]

Fair enough. Will get purchasing now

Thanks for the help guys!

[Jakstaar17]

Purchased