What kind of filter is this ?

[crepitis]

I bought a 1.25" filter from E-Bay which the seller had listed as a

"Nebula filter" and said that his father had purchased it from Broadhurst clarkson and fuller in the 1980's . The filter is in seemingly perfect condition , but the only clues to its identity are the words "Japan" and "HF" around the outer edge. There is a small sticker on the box it came in which has the word "nebula" printed on it but there had been another word preceding it which has been torn off.

I just wanted to know if someone could tell me what the HF stands for and if indeed it is likely to be a Nebula filter, and if so, what would be the best targets to use it on for visual stuff only.

I havent owned any filters before (other than a polarizing Moon filter) and as this was a bit of an impulse buy I hope I havent bought a dud.

Cheers, Bob.

[drummerp]

Hi there,

Does it have any colour or is it clear ?

If clear it could be a lunar filter or an infrared filter.

Never heard of a Nebula Filter, maybe some of the more experienced members might know.

by the way - HF stands for Hafnium, its a compound element

Cheers

Neil

[John]

Hi Bob,

In my late 1980's BC&F brochure (yes I AM that sad !) they list a BC&F Deep Sky Light Pollution Filter in the 1.25" size. They say that it's intended for "general deep sky use under light polluted skies" it then goes on "Although mainly intended for photographic use, these filters will suppress background glow and increase contrast on a variety of deep sky objects".

The catalogue also lists a Meade Nebula Filter with similar characteristics.

My guess is that these filters are the equivilent of todays broadband filters such as the Orion Skyglow.

If BC&F were selling it than I doubt it would be a dud.

John

[crepitis]

The filter has a coloured coating which appears to be violet or purple.

[crepitis]

Thanks John, I will only be using it visually, so hopefully it wasnt just intended for photographic use.

[drummerp]

As jahmanson says, its likely to be something like a reduction/pollution filter.

Cheers

Neil

[crepitis]

Just had a quick look at Orions Skyglow filter on an astro shops site and the coatings on the filter look almost identical to the one I have, I will try it out tonight as we have lovely clear skies here (so far ! )

[BlueAstra]

I have a spectrometer at work which could measure its spectral response. I've posted a couple of curves for two of my filters, a moon and LPF filter.

[Astro_Baby]

Sounds like a light pollution filter - my Sky-Watcher LPR is a pale violet color.

[crepitis]

tried it on Saturday night and to be honest couldnt really see any difference in anything that I looked at.