OIII filter

In the Deep Sky forum, folks were discussing how great the "OIII" filter is. I tried to look that up at Anacortes and couldn't find it.

So, a beginner's question: What is it, and what words do you use to search for it?

Thanks

Bob under clouds

Try O-III, making sure that is an Oh, and not a Zero.

I found 2 of them just now at Anacortes.

They are "Narrow Band" Filters. This means they let through only a narrow band of light. Out of the whole spectrum of electromagnetic energy that may be available, they let in only one small part. This happens to be a part that is particularly strong in some types of objects. (I forget which). The light is strong in these objects because it is the color of light emitted by doubly ionized Oxygen--which makes up that particular type of object.

Since all light is diminished except that color of light, the contrast is increased, and the object shows up better.

Alex

Go to http://www.lumicon.com and review filters. The site will show spectra for each filter type showing what is blocked and what is transmitted. Their diagrams are excellent and will be very informative.

Here is a link with some more info:
http://pages.sbcglobal.net/raycash/filters.htm

I've found my UHC Lumicon to be a bit better combo with my small(+/- 4") scopes on more targets. It lets through more light. The OIII clearly has a more dramatic impact for me in combo with more aperture. Check the classifieds. They do show up, but go fast.

If I understand correctly, the transmission varies somewhat between different brands. I think the Lumicon OIII is more restrictive (darker) than some of the other brands? But I've no real first hand experience with others.

I have two O-III filters and two UHC Band Filters and I do find that many objects seem to show better with the UHC. There are some that the O-III shows the best, like the Veil, but a lot of others seem more detailed with the UHC.

Robert,
Floyd raises a good point.
I would say 80-90% of nebulae are better shown by the UHC filter.
So you might consider trying that one first, if you have no nebula filters yet.
Still, the O-III is very much better on certain objects, and you'll probably want to own them both eventually.
The O-III is worth having, just for the view it provides of the Veil nebula, one of my favorites.
There happens to be a 2" O-III in the classifieds right now, at a pretty good price:
http://www.astromart.com/classifieds/details.asp?classified_id=401012
Have fun!!!
Linton