The UHC world.. Confusing!

[zhgutas]

Ok, first of, not sure whether this is a correct section for this - if not, please feel free to (re)move. And it may as well just be useless, as there is so much written about filters by people who actually Know what they're talking about, rather than some absolute noob (me) rambling about it. Please note, I do NOT have any first-hand experience with filters, and all this gibberish is merely what I have read, my "journey into choosing a filter" without actually trying one, and thus, it is probably more like an elaborate (VERY elaborate) question, rather than an answer However I do hope the simple graph I collated from few sources will help someone visualize the difference in these rather common filters. I offhandedly made it for myself to understand all this thing better, so I thought I would share.

I've been recently reading A LOT about various equipment in order to educate myself as best as I can before purchasing a more serious kit, as I want it to last quite a bit. One of the areas of "research" was, of course, filters. And oh my (nothing shocking here) have I found it confusing and overwhelming. Sometimes I do feel like not having a huge freedom of choice, makes life a heck easier After spending hours and hours browsing through posts and various sites, I kind-of made my mind up upon choosing an UHC filter over an OIII for visual use. That was until I found out there were (again) plenty to choose from, and they all seamed different!! Spending more hours reading, only seamed to make things worse (a common practice, I believe ) as there was no strong agreement upon which one was "the best" ( I know I know, "there is no such thing", ).

While some people say a Baader UHC-S is really nice and bright, others complain it does not make that much of a difference and that a "simple" UHC (whichever) is better, since it gives a better contrast. Then the "baader people" respond by calling the sight unnatural and so on and so on... ( I probably must add, I read all the reviews having in mind my future-scope - a SW 200DS, and its moderate (apparently!) aperture).

As far as I understand now (and I can really be wrong here), roughly speaking, the "broader" the filter - the brighter the overall image. However less contrast, as nebular line can be somewhat "washed out". Narrower filter - means more contrast, but fewer background detail. UHC filters, being able to transmit both OIII and Hb are "brighter" than pure OIII, but have less "definition" or, sharpness, if you will. However in the same UHC family, there are some substantial variations: TS UHC (very similar, AFAIU, to Orion and Lumicon) seams to be inferior in total VISIBLE light transmission than that of Astronomik. In fact, by studying the transmission graphs, it is obvious that Astronomik UHC is much more similar to Baader UHC-S and even Astronomik UHC-E, than to "true" TS UHC (and the Lumicon, for that matter), mainly because it also transmits INVISIBLE Ha line. It also seams to be a tiny bit superior to the TS UHC in transmitting OIII.

All this kinda pushes me towards choosing either UHC-S, -E, or an Astronomik UHC. Budget forecast not looking good for an Astronomik UHC (£150 for a 2"! ouch!.. ), so UHC-S and -E must be in the head-to-head battle here. IF my crude collage is right, it seams UHC-S is ever so slightly wider tan -E. Could be argued how noticeable that is though..

Now here comes the question:

both filters, whilst being "visual", transmit invisible Ha. I've read SteveL's comment on using visual filters for imaging and was wondering, a) how soon does this become evident (i.e. what exposure length), could this be avoided by adding an IR filter? using non-modded DSLR? Would be nice to know any of these filters would also add even a wee difference to some imaging. I'm not talking really serious stuff, just fun with a camera and a 'scope

All in all, do my thoughts here sound at all correct and am I going the "right" way in choosing UHC-S, -E over the UHC?

Cheers

Marius

[John]

I think you are taking a very considered approach to this. I think your decision will be influenced on the scope that you are going to use the filter with. If it's your ST80 then I'd suggest the UHS-C - I managed to see the Veil Nebula from my back graden a couple of years ago using that combination, which I was rather chuffed to do.

If however your plans for a SW200P mentioned in your sig come off then you can be more flexible because of the greater aperture.

I "graduated" from a UHC-S to a 2" TS UHC then to a 2" Orion Ultrablock (which is essentially a UHC as well) and now on to an 2" Astronomik OIII (visual) which I find an excellent "one filter" solution for my needs (I don't image) because it's band pass width is a little wider than some OIII's. I did try the Baader OIII en route but it's band pass width was too narrow for my tastes.

Of the UHC's I've used I reckon the Orion Ultrablock was possibly the most effective. David Knisely (Cloudynights) rates it well too in his reports on filters.

You are right though, it's a confusing world of filters !.

[acey]

I only ever bought one filter, a Lumicon UHC, nearly ten years ago, and I've never regretted it. I've used it with scopes of 80mm, 8-inch and 12-inch aperture, all with good results. With the 80mm I got a great view of M76 from my heavily light-polluted back garden, and I recall a memorable view of the Skull Nebula when I took the little scope to Greece. With the 12-inch I've seen the Horsehead at a dark site. With the 8-inch and UHC I've viewed Veil, Rosette, Flaming Star (flaming hard!), Thor's Helmet and many more. Great filter, worth every penny, and I've never felt the need of another.

To be honest I've never understood why aperture or f-ratio should make any difference in terms of filter usefulness; I've found mine equally good on any scope. In my experience what really counts is blocking stray light, because the filter is very reflective and if there's light on the eyepiece it'll bounce straight back into your eye. At light-polluted sites a hood can be used if need be.

[zhgutas]

Thanks for your replies guys. And, John, yes, as I said I am mainly thinking about SW200 when choosing the filter. Though it'd be nice to try it with the ST80 sometimes, as that's just a superb "go-everywhere" scope, and I literally, take it everywhere where there's a possibility I'll get any time under a dark sky (that's when I'm home, that is ). but I reckon, I'd then buy an UHC-S(-E) for this separately (in the not-so-near future:) ) since ST is also only threaded for 1.25" IIRC.. And I've read (and bookmarked!) David's page. Superb amount of info!

Acey, AFAIU, the earlier Lumicon filters differ from the current range, one of them being wider, though I'm not sure which one.. :/ (the graph attached shows Lumicon transmitting Ha)

And yes, aperture thingy and filters are quite confusing too. I've read this article on aperture vs. light pollution, which may somewhat explain the issue, giving that what a nebular filter essentially does, is get rid of any "light pollution" for the desired target image, therefore possibly including star light as well.

All in all then, going for a "pure" UHC as John suggest, may be OK for 8", as less "non-nebular" origin light is transmitted, thus, increasing contrast. (then again, I guess I won't know until I try several filters myself what is my "comfort level" on contrast, and how "aggressive" a filter can I be happy to use :? ) But my question on possibility of imaging, still bothers me a tad as well

Marius

[Andrew*]

I'm one of those who prefers true UHCs to broadband UHCs. I also get on fine with OIII filters. My take on it is if you're going to isolate an emission line, do it properly! Yes, you will lose stars, but you'll lose a lot of background light too, and therefore enhance the nebula. In no aperture scope will you lose nebulosity using a UHC. While I haven't tried an UHC in a scope smaller than 4", I don't think you'll get ill effects. I have heard reports of amazing things being done with 80mm scopes and OIII filters...

All just MHO! I know others feel differently.

Andrew

[zhgutas]

I guess then I only know when I try a few myself then huh?

Marius

[Space Bat]

I can't speak for other filters as I am firmly in the Astronomik camp of preference for filters.

But the UHC is an amazing filter - and provided very good views for almost every DSO, I am however in lighter LP area so have much darkers skies than most, but I do suffer from a little in one direction and that is where you notice how good the filter rejects LP.

Not everyones eye response and sensitivity is the same, so graphs alone are not really a help when it comes down to choosing the subtle differences between manufacturers - so people will obviosly get different things from filters - so it does become subjective.

I chose to go the Astronomik route due to reputation alone, yes they are more expensive, but you only need to buy them once - so chose the best I can sensibly afford knowing they would last my lifetime.

Chris

[Andrew*]

Another one worth considering is Skywatcher's UHC. Probably the best price on one you'll find anywhere, and IMHO every bit as good as the Orion Ultrablock. I tried them side-by-side and couldn't tell the difference between them.

Andrew

[zhgutas]

Another one worth considering is Skywatcher's UHC. Probably the best price on one you'll find anywhere, and IMHO every bit as good as the Orion Ultrablock. I tried them side-by-side and couldn't tell the difference between them.

Andrew

Hmm not even though about this one for some reason Looking good at almost £40 cheaper than UHC-S new. Though that still leaves my question about possibility of using UHC's that transmit Ha (as UHC-S or -E) for unmodded DSLR astrophotography, valid .

Marius

[haitch]

Marius - You've put perfectly into words what's been going on in my head.

Andrew - Thanks for your thoughts on the Skywatcher UHC. I'd been looking at those on FLO's site but hadn't seen any reviews. I was also interested in the 2" OIII for my 14". Has anyone ever used and have an opinion on the SW OIIIs?

[Andrew*]

I have one. The views are great, but I haven't compared it with any other brand..

Cheers

Andrew

[haitch]

I have one. The views are great, but I haven't compared it with any other brand..

Cheers

Andrew

Thanks - I think I might have the confidence to save a few quid by going for the SW when I've saved up a the readies (must stop looking at the classifieds!)