OIII filter question

[nitram100]

Hey guys,

So I just received a second hand Castell 2" OIII filter and tried it on ring nebula etc and it really is nice, but I held it up to the light and there appears to be a small pinhole sized area where there is no coating, would this affect it at all?

[m37]

Welcome to SGL. Sure the small area won't make much difference to overall images but have you tried a VERY careful cleaning to see if it actually a speck of something? If it was an ebay job and wasn't mentioned in the listing you could always return it?

cheers

[NGC 1502]

If it is a pinhole size area, it won't affect the view ( just like a bit of dust on your telescope mirror doesn't matter)

As in post #2, are you certain it won't clean off ? I use a microfibre cloth and isopropyl alcohol - plus great care.

An OIII is brilliant on the Veil Nebula, can see it easily with mine even from my light polluted back garden, using the same scope as yourself.

Regards, Ed.

[nitram100]

Thanks guys will give cleaning it a go tonight when I get in from work and also look out for the Veil! Dumbbell Nebula was amazing with this filter.

[Northern Soul man]

Hi Ya Nitram, shouldn't let it worry you mate, I have the Castelli OIII and the UHC 2" filters and can't remember which 1 has a small "hair" mark, but its very small and remember these filters "block" a tremendous amount of light passing through them and only let a very small amount of narrow parts of the visible spectrum through, also they're highly reflective, so by the time the light has travelled, in some cases, millions of light years from these "really faint" objects and then passed through the "dirty" atmosphere down to our (in relative terms) tiny " miniscule" mirror/lens systems we are using, there's any wonder these tiny pieces of glass work at all!!

No really mate don't let it worry you, I've been gazing for years and used loads of different scopes, there's still a load of gazers on here (and I used to be 1 of them) that spend more time looking through their scopes "THE WRONG WAY" (looking down at the lens/mirrors) WHEN THEY SHOULD BE LOOKING DOWN THE OTHER END OF THE SCOPE ?????????

Think about it guys an gals I AM RIGHT AREN'T I. Joking aside mate, don't get hung up on every lens/glass surface having to be totally clean - it took me years to get out of the habit and still do it from time to time now - see I told ya. Regards Paul.

[nitram100]

haha, thanks Paul that is reassuring! Just out of interest mate, how do you find the UHC compared to the OIII? Would it be a worthy purchase? Or should I just stick with the OIII? Thanks

[Northern Soul man]

Yes mate, with that light bucket each filter will be a bonus for ya, each filter works in blocking different wavelengths, the OIII works especially on the Ionised regions surrounding the object and are dependant on the mass/type and composition of the surrounding region and the light thats making the object visible - the OIII works on only a certain amount of objects and the UHC is more of a "broadband" filter which tends to work with far more objects and not specifically ionised regions. Also, the place where you observe from plays a massive part in actually observing these objects where light pollution plays a massive part as well - the more the light pollution you have the lower the contrast will be so this adds to the fact as wether you see the object or not - I say objects but these can either be Planetary nebula, emission nebula and even to some extent the "star forming" regions - like the Orion and Lagoon nebulae - these brighter nebulae really benefit from these filters as they are very bright to begin with, the planetary nebulae also work well under moderately light polluted skies (well the brighter ones) at low powers they become star - like, but increase the power a little and place the filter in line, you get an idea of the size and power of these "star forming " and "star dying" regions - like the "eskimo" and the ring nebula, even making the "Owl" nebula visible with the filter and invisible without - on some objects they work that well.

So the UHC will work on more objects than the OIII but they both generally darken the background sky and give you "false" coloured stars.

I also have the Baader O III and the UHC - S, but the Castelli filters are really good filters for the money, I think the only difference with them is that (compared to the Baader) the transmission lines are a little more broadband letting a little more "light" through them and I think the coatings on the higher priced filters are a little more robust - but, as far as I can see, thats all !! - trust me - I've tried all the different filters on many objects from the Midlands light polluted skies and they do work, much better on some objects than others - making the invisible - visible, just giving false colour stars and a much darker background sky. Hope that helps Paul.

[nitram100]

Wow, thanks so much for that Paul. I will definitely keep an eye out for a UHC filter!

[John]

My personal favourite is the Astronomik O-III. It's one of the more expensive filters but renders stars more accurately than others I've used (eg: UHC's and O-III's by Baader, Orion (USA), Telescope Services and Skywatcher). The Astronomik O-III has a slightly more generous band pass width than other O-III's with the result that it's really effective in all my scopes from 4" to 12" aperture and the enhancement of contrast in nebulae is really significant in some cases, eg: the Veil Nebula. I find it the only narrowband filter I need

[Northern Soul man]

Thanks nitram and nice 1 john I think that over time using these filters becomes a personal thing a lot of gazers seem to get on ok with them and others really don't like the views through them. I think they seem to enhance certain objects better than others but taking all into consideration like aperture, light pollution, sky conditions you have to look at the whole picture in the same way as you can look through the eyepiece at any given object, but just before you do, think of the object photographically and then take a look through the eyepiece - a totally different experience all together. Nice thread guys an clear skies to you all. Paul.