OIII filter question

[Tom Wales]

I recently purchased a Teleview 1.25" OIII filter, tonight was the first
chance I have had to use it and the only target I could find from the highly
light polluted skies of my apartment complex was the ring nebula. Using the
filter made it stand out much better than without. I decided to look for the
Veil nebula and while sweeping the area where it should have been I noticed
that while most stars in the FOV looked white there were a few that showed
up green. Some would blink from green to white and back to green. I never
did find the Veil which I attribute to the light pollution. Anyway the
question is; why do some stars look green through the OIII filter and others
white? And why do some seem to blink between white and green?

Thanks and Clear Skies
Tom Wales

[Nicola Montecchiari]

Tom Wales wrote:

That filtre is made to be used also in light polluted skies so you should see it.


A complete answer would require a university degree course in Optics. Briefly: the filtre is made with multiple interference layers that should be used at the centre of the field of view. As soon as you move the stars progressively far from the centre of the field of view, the different interference layers of the OIII do interfere in a non optimal way, and that is the result you see.

Nicola
http://astrofoto.laza.it

[justbeats]

"Tom Wales" <bbjazzman@nospam.verizon.net> wrote in message news:<3fq8d.10000$na.9122@trnddc04>...

The color receptors in your eye are most sensitive in the green part
of the spectrum. Under low light conditions, the color receptors stop
working and you only get black and white vision. If a star were dim
enough to be on the edge of colour perception, your eye will be
flipping between using the rods and the cones which you would see as
blinking between colour (green) and b&w (white).

I suspect it was the brighter stars that appeared green and the dimmer
ones white. The ones in between blinked...

I'm sure I'll be corrected if I'm wrong :-)

Cheers
Beats

[Tom Wales]

Nicola and Beats, thanks for the answer. What you said makes a lot of sense,
thinking back on it the green looking stars were the brighter ones and they
were only green when they were out of the center of the FOV.

Clear Skies,
Tom

[Canopus]

"Tom Wales" <bbjazzman@nospam.verizon.net> wrote in message news:<3fq8d.10000$na.9122@trnddc04>...

The OIII filter has passband in the green portion of the visible spectrum. See -

http://www.lumicon.com/filterspec.htm

- Canopus