white light pollution - which filter?

[obscura]

I realise that there have been many Q&As on this perennial subject but I have yet to see any Q on the new street lights being installed in the county.

In addition to the usual air glows we are blessed with white street lights in Hampshire and I am perplexed as to the correct filter to shade this pollution.

I have looked at SW, Baader Neo, Astronomik CCD-CLS clip and Hutech Idas P2 with tags of £26 to £163 for a clip/2". But which is the most effective (and cost effective) to deal with this LP.

If a clip, it would run behind narrow band filters - is this OK wrt reflections etc?

I have read conflicting comparisons but overall the Hutech seems to be the preferred. But would a SW at £26 also fit the bill for this Hampshire light?

Apologies for raising this old timer yet again.

[Steve Ward]

On the grounds that the targets you're looking for are generally made of "whitelight" there's no way of filtering out the streetlights without losing all those things you're trying to observe I fear.

[davew]

This certainly could be a problem. We as astronomers are pushing for less and shielded light. Up go LEDs that seem to be well shielded. All good so far but if the shielding isn't up to scratch or the light is above your camera then you may be stuck.

Overall the new lights may increase the night sky for the majority and the larger observatories but for a minority of us it's going to be a nightmare. I've seen the general effect on street lighting and it's quite positive. I've also stood below one, at a distance, that was on a slight rise and there's no escape !

Dave.

[obscura]

Its true that the light is directed downwards into the road but sadly from a greater height. The lights are upper bedroom window height  though shields were added to the light to reduce the intrusion. Mind you that can pale, pun unintended, into insignificance with those "megawatt security lights" that automatically come on for a passing cat etc.

I am shielded from the lights directly due to trees we established some years ago but that doesn't stop glow.

Having said all that, one cannot be put off by external intrusions and persevere.  I guess most of us in the UK are in some way affected by LP, weather, cloud, fog, rain, snow - what have I missed.

But what filter would assist? The narrow bands will be very effective for the nebs etc but not the galactic whirlpools up there.

[Steve Ward]

You filter out the streetlights you filter out the stars and galaxies ... 

[russellhq]

Narrowband filters maybe...

[obscura]

Thanks for the input everyone. I realised that there would be a trade off in filtering white light which is the reason for the question. How do others cope with the problem and how. A house move. Not an option. Sell up and take up calligraphy. I don't think so. The best alternative is therefore filtration. 

It seems that any LP filter would be a waste of money. As we know, any light pollution comprises many different sources and reducing any of those would help. The white light I speak of is from easily identifiable sources but none are in line of vision or line of optics. Thus it is their limited "afterglow" that would be good to reduce. Perhaps the white aftergow mixes an dilutes with other afterglows up there? I am likely to invest in the SW LP and take it from there but I am unsure if it has IR cut. That would be an important factor. My narrowbands will sort the nebs.

Cheers

[Steve Ward]

Again , you cannot filter out the "white" lamps without filtering out the stars and galaxies .... 

And if the "narrowband" you're aiming for falls in the visible spectrum then filtering the "white" will kill that too.

Your best bet may be finding a "dark" site nearby that you can operate from , a bit of a drag but it's the only easy way if you're unfortunate to be stuck in LP I fear . . . . 

[obscura]

Oh. Again.

Why would I filter out white with an Ha or O3 or S2 filter on board? Do I make myself out to be that naive??

We all know something of the nature of light and know that white is a mix of all colours. So any filter will affect the colour of any object be it white or any other colour. There is no such thing as a white filter - maybe a black one? Thus it is clear that a filter on any colour including white will change its hue.

This sends me back to my film imaging and processing- in colour.

Enough of this.  I'm outta here

[russellhq]

I don't think anyone is saying you can filter out white light. What you can do is filter out unwanted noise while allowing the signal (and less noise) to pass though. This should have the effect of increasing your signal to noise ratio which is what we are all trying to do.

[obscura]

Hi Russell (hope that's correct)

Of course white light cannot be negated by filter and hold all stellar objects in place. That' plain daft and obvious.

However, filters isolate given angstroms or negate unwanted nms if preferred. Ha, RGB etc. Removal of a bit of the visible spectrum.  It depends what one is looking for. In this case I was looking for the best alternative from perhaps someone with similar conditions.  Hampshire.

So. Exactly as you say. Improve the s/n by filtration albeit general LP.

(Regrettably, going to a dark site is not an option either. In the first place all my stuff is mains powered but more importantly, I'm just too old to be standing out in a field in sub zero conditions. C'est la vie:)

Thanks for your input.

[davew]

Oh. Again.

Why would I filter out white with an Ha or O3 or S2 filter on board? Do I make myself out to be that naive??

We all know something of the nature of light and know that white is a mix of all colours. So any filter will affect the colour of any object be it white or any other colour. There is no such thing as a white filter - maybe a black one? Thus it is clear that a filter on any colour including white will change its hue.

This sends me back to my film imaging and processing- in colour.

Enough of this.  I'm outta here

This " Problem " is probably not as bad as it seems. If you want to filter out Sodium then use a Sodium filter. For Mercury a Mercury filter. Same goes for UV and IR. Luckily for us the filter manufacturers have sussed this and sell LP filters for most light pollution.

Now your telling us you have white light pollution. If they are in fact White lights then it will probably cover the range from below 400 nm to over 700nm. To filter this light out you probably already have the correct filter. It's commonly know as a dust cap !

In the HIGHLY UNLIKELY event that Hampshire CC are directly targeting you by surrounding your property with white lights and directing them at your garden then you may not in fact have a problem at all. In theory at least, the sky above these lights should get darker and the streets below get brighter. Win win for an insecure public and us trying to see the stars.

There is an upside to white lights I believe. In future if you are unlucky enough to be run over by a hit and run driver, you will be able to tell the Police what colour the car was.

If you are using a narrowband filter you don't need an LP filter.

You may not like what Steve has to say but I think you should at least thank him for wasting a few minutes of his life trying to answer you.

Dave.

[obscura]

Hi Dave.

i thought I had closed this down, but those that do bother deserve a response.

It wasn't that I didn't like Steve's comments. Not at all. It was more that it was repeated over and over. I was looking for constructive ideas etc for reducing the problem - as Russell said improve s/n.  That was constructive and helpful. Surely one can ask a simple question and get a simple answer. I wonder.

Whatever. Oh. If one looks back, I did thank all.

Did I detect touch of fasiciousness here?

SGL and its members were more than helpful to me in the early years and I have many to thank for advice given, and taken. Due to my wife's serious illness throughout this year I have been out of the loop and got somewhat rusty hence an odd question here and there.

But, it is of no consequence. If responses such as these are now the norm, I will not bother SGL again

What a shame - was such a nice place to chat.

I really am outta here.

[davew]

Hi Dave.

i thought I had closed this down, but those that do bother deserve a response.

It wasn't that I didn't like Steve's comments. Not at all. It was more that it was repeated over and over. I was looking for constructive ideas etc for reducing the problem - as Russell said improve s/n.  That was constructive and helpful. Surely one can ask a simple question and get a simple answer. I wonder.

Whatever. Oh. If one looks back, I did thank all.

Did I detect touch of fasiciousness here?

SGL and its members were more than helpful to me in the early years and I have many to thank for advice given, and taken. Due to my wife's serious illness throughout this year I have been out of the loop and got somewhat rusty hence an odd question here and there.

But, it is of no consequence. If responses such as these are now the norm, I will not bother SGL again

What a shame - was such a nice place to chat.

I really am outta here.

There are a few thousand members of SGL. I wouldn't allow one, me, to put you off coming here in the future and taking part. I rather doubt my response is now the norm.

We all have our ways and maybe Steve thought you weren't getting his direction. The main objection I had to your response was " Enough of this, I'm outta here " 

Fasiciouseness ? A touch I suppose and I'm sure I will be contacted in the near future.

Dave/

Please give Mrs Obscura my very best wishes for a full recovery.