whats an OIII filter

[stargazerkelly]

I have no clue as to what a OIII filter is?

any help

[steppenwolf]

An OIII filter transmits only the two OIII emission lines that appear within the light spectrum that our eyes can see within the green part of the spectrum. There are lots of deep sky objects that emit light in this region and using an OIII filter increases the contrast of these objects making them easier to see against the background sky.

[stargazerkelly]

Steve

WOW How Much are OIII filters

i have a 12" dobs wil this improve my viewing of DSO's

[Moonshane]

the way they work is to effectively remove any light other than those channels which they allow through and as Steve says that some DSOs emit. what this does is reduce how apparent the background sky and to some extent the stars are and increases how apparent the DSOs (that emit the right kind of light) are. e.g. the Veil Nebula is impossible from my garden without the Oiii. even with my 6" scope I can see the Veil clearly when the sky is dark (albeit still light polluted).

I use the Castell Oiii which is about £50 delivered for the 2" version, extremely good value and very good quality. I fit mine either to a 2" eyepiece or to the 2"-1.25" adapter (or you can put it on the diagonal.

Castell OIII Deepsky Filter for 2-Inch Eyepieces [Castell-Doiii2] - £46.56 : 365Astronomy: Discovery for every day!

[Skylook123]

As well stated above O-III, or doubly ionized oxygen, is present in certain Deep Sky Objects. Most generally, it is a byproduct of planetary nebulae and supernovae as new elements get generated at the end of life of a star, but there can be interesting effects in emission nebulae around hot new stars, if they are in a region of stars now gone that mixed in the O-III and other debris with the hydrogen cloud. Personally, I think it is the most singly important filter in my case. As stated above, unless you are at quite high elevation in extremely dark skies, The Veil is invisible without it. With an O-III, The Veil pops like a waving curtain, and while The Dumbbell may look like a faint smudge without a filter, it almost falls into your eyepiece with an O-III.

Many times I use an Ultra High Contrast filter instead; this allows an H-Beta line along with the O-III. The UHC will make all of the eye candy in Sagittarius scream back; the Swan will grow more feathers with the UHC, and almost any target for O-III does quite well or better with UHC.

There is one trick to using these narrow band filters, and that is to stop the light from coming past your head and reflecting off the surface of the filter. What it stops coming down the tube will also reflect to your eye, so it helps to have some sort of hood blocking the light. One can also use one's nose on one side of the eyepiece, and a hand around the eye on the opposite side, to block out the stray light from behind. An old pair of workout short pants makes a nice hood, and who can see it in the dark, Eh?

[Moonshane]

There is one trick to using these narrow band filters, and that is to stop the light from coming past your head and reflecting off the surface of the filter. What it stops coming down the tube will also reflect to your eye, so it helps to have some sort of hood blocking the light. One can also use one's nose on one side of the eyepiece, and a hand around the eye on the opposite side, to block out the stray light from behind. An old pair of workout short pants makes a nice hood, and who can see it in the dark, Eh?

this is an excellent point and I completely agree, especially when neighbours leave their kitchen lights on! a cupped hand is enough really but a hood is better. I find a dark towel or even a T shirt worn up instead of down works well too.

[swamp thing]

i have a 12" dobs wil this improve my viewing of DSO's

As has been stated these filters work very well on emission Nebula, but they have no effect on reflection Nebula.

They are obviously of no benefit on star clusters and Galaxies unless using one to spot emission nebula within an external galaxy.

Eg NGC604 within M33. Which is easily do-able with your 12" Dob.

Regards Steve

[Moonshane]

nice one Steve

I'll look for this in the 16 when it comes around (not long now).

[todd8137]

i have the said filter works great on my 12" reflector ,as peeps have said works well on some but not on others ,i get better views of viel neb, m42,dumbell