OIII FILTER

[oldfruit]

Hi,

I am interested in looking at more planetary nebula and nebula in general and have read that an OIII filter can help, but when i have read info on the sites that sell them they have said that they are really only any use on telescopes of 200mm aperture or more.

As i am using a 200mm telescope i will be at the lower end of useful aperture.

My question is will a telescope of my size show a great deal of difference if i use one of these filters when observing visually?

Thanks.

Mark.

[John]

An O-III filter is a very useful tool for enhnacing to contrast of nebulae. Without one the views I would have of objects like the Veil and Owl nebulae would be very dissapointing. Some O-III's are "harsher" than others (ie: their band path width is narrower) but you should be OK with even those with 8" of aperture I think.

My current OIII filter is a 2" Astronomik O-III which is really excellent in all my scopes from 4" to 10" in aperture. There are other, less expensive options like the Castel ones which I've not used personally but I see reports from others that they are good.

[russ]

I've been using the Skywatcher 2" OIII for just over a year now, very impressed. It replaced a 1.25" Lumicon OIII. I did a quick comparison before selling the Lumicon and was very satisfied with the way the Skywatcher performed. At £59 the Skywatcher is at the budget end of the scale.

[Andrew*]

A second recommendation of the Skywatcher OIII - very pleasantly surprised. I have the 2" version.

Baader's is particularly narrow at 7nm, but they also do an 8.5nm one.

As for the question, they will do just fine in your scope. I believe it's a complete myth that OIII filters shouldn't be used in small scopes. While some may find the view gets too dim in the eyepiece, it's undeniable that the contrast increases on nebulae. I have seen the Veil nebula in only 80mm aperture using an OIII filter under suburban skies.

Andrew

[russ]

You're right Andrew, it's an urban myth that OIII filters don't work well with small apertures. I've used the OIII with the Celestron wideview 102 to get a lovely widefield view of the Veil. Picked it up no problem from my light polluted sky. Even better from the dark site. M27 and M97 both responded well to using the OIII with the 102.

[oldfruit]

Thanks guys for the replies. I have seen the Skywatcher one and the price looks good as in not too expensive. So think i might give it a go.

Really appreciate the advice.

Thanks again.

Mark.

[ollypenrice]

Never heard this 'small apertures' stuff before but it's nonesense!!! I had great results in a 4 inch Genesis.

Olly

[John]

The only O-III filters that I've found dissapointing in 3"-4" aperture scopes were a Baader O-III and a Celestron O-III (the latter was actually the Baader re-branded !).

Personally, I prefer to see DSO's in the context of some background stars, and I found the narrow band pass width of these led to almost no stars being visible at times with the modest apertures, although the contrast of the nebula itself was noticably enhanced. Maybe thats just my odd taste in views through !.

[oldfruit]

In my original post i mentioned aperture. I`m no expert and that is what it says on the website, but as we all know, unlike some brands, they don`t always do exactly what is says on the tin. This is the only reason i mentioned it. Thankfully i can ask you guys that have actually used them and get an impartial opinion and a realistic expectation of performance.

Thanks again guys.

Gotta love SGL.

[russ]

Be good to hear how you find the OIII when you get it. It makes a real difference

[bish]

Funny as I was always under the impression that you need a big scope for an OIII. Some suppliers even advertise this (although I've not looked for a while). This stopped me from buying one for my 6" and cautious for my 8". If the Skywatcher gives decent results at £59 then I think I will have to get one.

[oldfruit]

Minds made up now. I will be buying one shotly and will post results when i get a chance to use it.

[Doc]

Which one are you buying?

I have the Baader O111 in 2" format and I know it's being used in a 16" but the views are stunning of certain objects.

I don't see no reason why it wouldn't work in a 8" scope.

[russ]

Funny as I was always under the impression that you need a big scope for an OIII. Some suppliers even advertise this (although I've not looked for a while). This stopped me from buying one for my 6" and cautious for my 8". If the Skywatcher gives decent results at £59 then I think I will have to get one.

I bought my OIII for the 200P and it really did make a proper difference. M97 for instance is only just visible from my backgarden with the 200P. But with the OIII, it just popped out. Same with M76, Eskimo (NGC 2392) and Snowball (NGC 7662). And it makes all the difference with the Veil.

[oldfruit]

I will probably opt for the skywatcher as this time of year with 4 kids i`m on a bit of a budget when it comes to astronomy plus it keeps the wife happy:).

[glowjet]

I was most interested to read that the authors of Illustrated Guide to Astronomical Wonders have confirmed that, not withstanding what has been said about the use of Nebula filters in large scopes, they were able to see the North America Nebula in an 80mm short tube refractor with the aid of an O111, which they were able to see quite clearly ( no doubt dark skies with good seeing ) without the filter the Nebula was not visible.

[John]

I was most interested to read that the authors of Illustrated Guide to Astronomical Wonders have confirmed that, not withstanding what has been said about the use of Nebula filters in large scopes, they were able to see the North America Nebula in an 80mm short tube refractor with the aid of an O111, which they were able to see quite clearly ( no doubt dark skies with good seeing ) without the filter the Nebula was not visible.

They do make a big difference, even with smaller scopes. With my 4" Vixen ED refractor, the 31mm Nagler eyepiece and the 2" Astronomik O-III filter I can see 3 portions of the Veil Nebula in the same FoV, even from my back garden - it's a lovely sight

Without the filter, the brightest portion of the same nebula is just about detectable, but only just and possibly only because I know where to look and what to look for.

[glowjet]

They do make a big difference, even with smaller scopes. With my 4" Vixen ED refractor, the 31mm Nagler eyepiece and the 2" Astronomik O-III filter I can see 3 portions of the Veil Nebula in the same FoV, even from my back garden - it's a lovely sight

Without the filter, the brightest portion of the same nebula is just about detectable, but only just and possibly only because I know where to look and what to look for.

Does it make any difference if you use the 1.25" as against the 2" version ( which should allow more light throughput ), it would be nice to know as it looks like I shall be having dip into the piggy bank again.

John.

[oldfruit]

Silly me, why did i not think to ask about the difference between 1.25 and 2 inch? All my eps are 1.25.

[John]

For lower power viewing I've used 2" eyepieces for a long time now so I've always tended to go for 2" filters - they can be used with 1.25" eyepieces as well of course but you can't use 1.25" filters with 2" eyepieces (obviously !).

If you only use 1.25" eyepieces (and don't expect to get 2" ones in the future) then the 1.25" versions of the filters are just as effective as their bigger brothers are.

[Talitha]

...they have said that they are really only any use on telescopes of 200mm aperture or more.

That hasn't been my experience... 80ST, 1.25" Lumicon O-III:

North America Nebula

Veil Nebula complex

I could see the brightening of the North American Nebula without the filter, but the Veil was invisible without it.

Enjoy your filter, Mark.

[Moonshane]

I think the key feature of whether or not these narrowband filters work well is the exit pupil size not the aperture of the scope etc. many of them will only work well with certain exit pupils (usually the larger ExPs created by lower magnification I think) but as always I bet these are rules of thumb so get one and try it. there's always a ready market for used ones so there's not much risk really and many people naturally increase their aperture over time so eventually they will be useful!

I use the Castell Oiii (also just ordered a UHC) and at about £50 for the 2" they are superb value for money.

Re 2"/1.25", I would recommend 2" if you can afford them, mainly as you can add it to your 2-1.25" adapter, diagonal, extension tube etc and not have to keep changing with each eyepiece.

[russ]

Silly me, why did i not think to ask about the difference between 1.25 and 2 inch? All my eps are 1.25.

Don't sweat this bit, as Shane says, definitely go the 2" route. It makes sense even if all your eyepieces are 1.25". You can interchange eyepieces without having to do anything with the filter, as the filter is attached to the 2"-1.25" adapter. Minimum hassle. Plus if you ever get a 2" eyepiece (highly recommended for low power widefield) you are set to go.

[russ]

Just seen your scope and alarm bells are ringing. Do you have the 2" adapter for it?

update: if you don't have the original 2" adapter, just found one on Ebay:

http://tinyurl.com/2v2pkdo

[oldfruit]

Just seen your scope and alarm bells are ringing. Do you have the 2" adapter for it?

Yes the scope is supplied with 1.25 and 2 inch adaptors so no worries there. I had often wondered about buying maybe 1 good quality 2 inch low power eyepiece for wide field views for things such as M31 but also for looking at things like The Veil Nebula and M42 with a filter.

I will have to check if my 2 inch adaptor has a thread to fit a 2 inch filter to, because as has been mentioned, if it did i would not need to keep changing the filter over every time i swapped eyepieces.

Thanks all for the replies. You have certainly given me a lot to think about and some good practical advice.

Thanks.

Mark.