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10-09-2009, 03:09 AM   #1
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Join Date: Jun 2007
Location: Brisbane, Queensland, Australia
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Hoya Nebula Filter ?

Hello,

I was looking through Dad's old camera gear and found a ' Hoya Nebula Filter ' , any idea what it's for, what it does ?

I googled it and come up with telescope filters called Nebula, but this is 49mm and obviously for a slr.

Rodney

10-09-2009, 06:07 AM   #2
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Join Date: Nov 2008
Location: USA
Posts: 924
optical filters, Schott, Hoya, Kopp, Airfield Lighting, Nebula filters, Wratten gelatin filters

NEBULA FILTERS



Night Image 1, 2, and 3 filters help observers to see fainter and more difficult targets. Light pollution falls into three types, NATURAL, LOCAL, and REGIONAL.



Natural light pollution called ‘airglow’ is caused by charged particles from the SUN bombarding oxygen in the Earths upper atmosphere. Its strongest wavelengths are between 560 to 630 nanometers. Whilst not discernibly visible to the naked eye, it may still decrease contrast in the eye piece to ‘hide’ dim targets.



Local light is nearby glare that infringes on observing sites from street light etc. A filter cannot stop this. All you can do is shade your observing position.



Regional light pollution is the real problem. Populated areas, roads and motorways pour light into the sky. These and other sources combine to create the orange gray haze we see above our cities and towns. The right filter can help to reduce this by suppressing the ‘bad’ wavelengths, but allowing the ‘good’ wavelengths from celestial objects to pass through.



The NIGHT IMAGE range of filters, are designed to dim and blockout the areas of the spectrum which are a problem. In doing this, the net visual effect is, ‘increased contrast’ between the object and the filter darkened background.

In short, it can enhance the visibility of the object.

The problem wavelengths are:

High pressure sodium vapour lights between 550 and 630 nanometers.

Mercury vapour lights between 405 and 436 nanometers

Low pressure sodium lights emit mainly a narrow region approx 590 nanometers
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