Oxygen 111 Filter Help Please

[BlackWidow]

Hello all. I have already posted this but I think in the wrong place.. I'm new to all this and its a big learning curve. I have a 10" DOB and a Celestron 80mm Refractor Nexstar GT goto. I recently purchased a Baader O111 Filter to help me see more detail in deep sky objects like nebs. I live in a lit location so I thought this filter may help me.

I was a little dissapointed to find it makes all that I am looking at have a green look as if you were looking through a green filter. Is this normal and part of getting more detail? or are thier different O111 filters that don't give this green colour? I have noticed on this forum people that have use these filters for photo's and don't seem to have a green look about them. I understand that we see different colours than a CMos or CCD see's. I was talking to another guy who told me his O111 filter does not colour the view at all. Have I got the wrong type?

If I look at the filter it has a mirror finish to it until you hold it up to the light. Then you can see the green colour like looking through an old green bottle..


Cheers
Mardy :help:

[Hagar]

The green is fairly normal. I certainly wouldn't have bought an OIII for visual use. It is a very narrow band filter which only allows a very narrow band of light to pass. It is used quite a bit for CCD imaging and is used to capture this narrow band of light but in a black and white format the colour is applied by photoshop or similar program.

A better filter for visual use would have probably been a Light polution filter or a UHC which will darken the background and increase the contrast on most nebulas.

Sorry to stuff up your day but I think you may have made the wrong choise in this instance.

[astroron]

As a general nebula filter a UHC is probably the better buy, but for Planetary Nebula you can't go past the O111.
It is not unusual to get the colours you describe, depending on the type of nebula you observe.
Stick with your O111 filter as after a while you will get used to it and probably enjoy it.
The only downside of the O111 is it darkens the stars.:(:(
but it brings out more nebulosety in Planetarys
Both filters can be used in Moon light as a light pollution filter to some degree:D:D

[Starkler]

This is what it is supposed to do. The filter only allows a very narrow passband of light wavelength through corresponding to OIII emissions. This light wavelength happens to appear green. You will only notice the green on bright stars.

All other wavelengths are reflected which can reduce their effectiveness in light polluted areas. Light entering the top of the eyepiece gets reflected straight back at your eye from the mirrored surface. It helps to throw a cloth over your head to keep ambient light out in such situations.

[mozzie]

martin dont be discouraged the oIII filter is great for nebulars its all trial and error i often use it and sometimes theres nothing to see and then wow have a look at that so its just patience and time
mozzie
ps try and look through a broad band filter

[BlackWidow]

Thanks to all that gave advice on my problem. I think the O111 filter may be great for the hunters, but I did not like the green colour and it seemed to make everything very dark. I think that I am so new to all this that I may get a better use from a O111 later on. I went into my local store and spoke to a few others. As on this page most people suggested that the UHC filter may be better for my general use for filtering out light in my area and giving me a better view of Most Neb's. The store I purhased my O111 filter from agreed to take it back and exchange it for a UHC-s.

I hope I have done the right thing:doh: I will let you all know as soon as I get the chance to try it out.

This is my best friends fault.....ALL OF IT...... If he had not shown me Saturn in his Mead ETX I would not be the owner of any Astronomy stuff, or filter selections :screwy: I think I've caught some sort of Bug!



Thanks all
Martin

[theodog]

I think you have.



Yep, it's a bug, and it sounds like you got it good.:lol:

Have fun with your gear.
:)

[Geoff45]

Unfortunately OIII light is green, just as H alpha light is red and OII is deep violet. That's the laws of physics and we are stuck with them.

[astroron]

Martin, you have just started a great journey in Astronomy:)
The further along the road you go the more you will discover and learn, the more you will enjoy:D
Lots of luck along the way:thumbsup:

[ngcles]

Hi Martin & All,



Congratulations on your new bug/obsession. Lots of sufferers here, you'll be glad to know that it is never fatal -- except to your bank-balance.

FWIW, with a 20cm telescope, I think you made the right choice with the filter by going for an exchange to the UHC -- however, be warned the UHC will still make bright nebulae look green.

To explain, there are four different types of visual general use filter for deep sky observing, The Deep Sky filter, UHC, OIII and H-Beta.

The deep sky filter is a broad pass-band filter that allows most light through but blocks most artificial light pollution. To quote the Lumicon website:

"The Deep Sky Filter is basically a general-purpose light pollution filter that restores a dark sky background for viewing and photographing deep sky objects from cities. It is the best light-pollution filter for all astrophotography on the market today.

Visually, the Deep Sky Filter is the most useful filter under light-polluted skies, from where it reveals star clusters, galaxies and nebulae."

See http://www.lumicon.com/faq.php

My personal opinion is that the deep sky filters are of no real use on galaxies and star clusters but perform well on nebulae. But if you are using it on nebulae, why not use a UHC?

The UHC is a much narrower pass-band that allows three separate emission-lines through -- The H-Beta line at 486nm and the twin OIII lines at 495 and 501nm. It dramatically enhances contrast on objects that emit on these lines and that includes most nebulae and the overwhelming majority of planetary nebulae. All three of these lines are in the cyan part of the spectrum

The H-Beta and OIII filters allow only the two above types of emission through -- H-Beta and OIII respectively.

The "problem" is that while these filters pass most of the "wanted" light at these bands (about 90-95%) and block most other wavelengths (this is how they improve contrast), they still do block some of the wanted light.

See: http://www.lumicon.com/filterspec.php

Because of that, I think the line filters (OIII, H-Beta) really only work well if you've got a lot of light available (ie a big 'scope). Personally. I wouldn't use them with less than a 10" 'scope.

On the other hand a UHC is very useful on 4-8" 'scopes because it has a wider pass-band.

But, remember because all three lines it passes are in the cyan part of the spectrum, the nebula if bright enough, will generally look cyan/emerald/lime green. The background sky will be much darker, but not as inky as with the OIII. Equally it will give a dramatic improvement if OIII and H-Beta emission is present. UHC filters will dim your view of clusters and galaxies etc -- don't use for these.

I own four filters for use on my 18" f/4.9: 2" -- UHC and H-Beta, 1 1/4" -- UHC and OIII. And what is my most used filter? The UHC's!


Best,

Les D

[erick]

Many thanks for this useful summary Les. Perhaps time for such an article in Oz S&T?

[StevenA]

My UHC filter still makes the sky a bit darker. The best bet is to find the object and home in on it first then put the filter on. My UHC is a Bintel brand and as far as I know all make the objects a little greenincluding UHC filters. This filter however has a plaesant green/blue colour. If you don't like the green at first don't worry you will soon adapt and it will not matter after awhile.

[ngcles]

Hi Erick & All,



Thanks for the suggestion Erick -- will keep it in mind.


Best,

Les D