LP Filter for low mag 2” EP

[Aronnax]

Hello all,

I have one more question related to eyepieces before I break out the credit card and have a little spending session to upgrade my EP’s. I’ve been reading as much as I can find on the forums and elsewhere about filters, and light pollution filters in particular. There does not seem to be a real consensus as some state that they make no real difference for visual, only to AP; others state that the Vatican should be called because they’ve witnessed a miracle.

I realise what these filters do, and how they work, and that it is partly only for marketing reasons that they are branded as 'light pollution' filters. My streetlights are not the very old deep orange low-pressure sodium ones, they are the brighter, yellowy/orange sodium vapour ones. But what I am really wanting from a filter is to cut down a little on the general orange sky-glow (even a little), and increase contrast when viewing at low magnifications, when this effect is of course at its worst.

As I will shortly be ordering a nice new 2” EP for low power viewing, I was wondering whether spending an extra £27 on the SW 2” LP filter would be money totally wasted or whether at that (relative) cheap price it is worth giving it a go?

I’ll only be using it for visual with the trusty SW200p Dob, in the low mag (x40) EP that will shortly be ordered.

I know filter discussions crop up often, but I’ve seen such polarised responses I wonder whether there is any middle ground, beyond - they either work or they are totally useless. I am not expecting world-changing views, but just looking to give a little contrast from the orange haze that is in the skies, and for £27 I don’t mind if it’s a slight improvement, so long as there is some improvement!

Thanks in advance for your thoughts.

[rwilkey]

Not sure if the SW LP filter will help you, I have just sold mine as it didn't get any use, if anything I think the Baader Neodymium filter will be more use to you I think. LP filters per say will be redundant soon as councils change their lights to the more modern white lights, orange sodium is disappearing fast.

[Stargazer_00]

Absolutely +1 for the Baader Neo. I have the 1.25" as a gift last christmas when i didnt have any 2" eyepieces and now im looking to sell it and replace it with a 2" one so all my eyepieces can benefit from it. It'd be esepcially useful in the 2" range when the sky glow introduced at low mangifications is more pervelant.

A really good test, ive found, is looking at the sky naked eye and then holding the filter over one eye like a monocle. It basically replaces orange to a blue tint which is much more pleasing on the eye. It does reduce overall brightness as it's a broadband filter, but by reducing the orange wash and darkening the background a little in the process I have found some DSOs easier to pick out. I think its a balance though really. The only things I really look at in wide field 2" eyepieces are open star clusters or galaxy groups. The neodynium in my lower magnficiation 1.25" eyepieces does reduce background orange somewhat and the DSOs are still visible although perhaps almost inperceptably dimmer as a result of the filter. For me the small loss of brightness is a worthy tradeoff for the replacement of that sickly orange.

When my streetlights go off after midnight I find the filter goes right back in the case for the rest of the night so obviously it has no use whatsoever if you are going to a dark sky sight. It is supposedly a moon filter as well but in reality it casts a blue tint on the moon which i dont like. I want the moon to be snow glare white

[alan potts]

Robin,

Will it be possible to filter the new type of lights?

Alan.

[Aronnax]

A 2" Neodymium filter runs a bit much (£££) for this round of purchases. Has anyone made a direct comparison between the neodymium and SW LP filters?

I take the point about broadband filters becoming less useful as LED lighting becomes the norm (at least for LP reduction purposes).

Thanks for the comments so far

[Stargazer_00]

My town has just invested heavily in the big switch off, so upgrading the infrastructure to allow select lights to be turned off at night. On that basis I dont see them investing in switching to LED lighting anytime soon. the 400k investment they reportedly invested is going to take 5-7 years to recoup before it becomes proftable. obviously it isnt all about the bottom line but rather the carbon footprint but im sure they can use this to justify keeping the easily filtered lights for some time yet. if/when the LED lights comes almost all our filters will be useless I read.

[rwilkey]

Hi Alan, it will not be possible to filter the newer led lights as any filter that does this will filter out all visible light, including the stars themselves. The best current solution is the Baader Neodymium as it is very selective, but no good for white light.

[Aronnax]

Has anyone got any links with the wavelength filter characteristics of the SW LP filter and the Baader Neodymium?

Clear skies (or at least not too orange)