Moon filter V's LP filter.

[LukeSkywatcher]

Early this morning (5-6am) i had my SW 130P Dob outfront because i wanted to spend some time with the Moon and Mars. I have a couple of orange street lights (the light from them is orange) directly across the road from my house. So i decided to give my new SWLPF a test drive. It worked amazingly well under these conditions. The sky above and between these 2 lights was a lot darker then without the LPF. GREAT.

I then turned the scope on the moon and left the LPF on the EP. To my amazement the LPF worked better as a moon filter then my moon filter. Contrast on the surface of Moon was much more obvious,sharper etc. The moon was also a more natural colour. I'd never noticed before that with the moon filter that it gives the moon a slight tint. There was no tint with the LPF (the glass is a purple colour).

Just wondering if i have stumbled onto something new here or if anyone else has had similar experience with a LPF.

[Breakintheclouds]

Paul,

That's really interesting. I have both those filters and will give the LP filter a try next time I look at the moon. Thanks for the tip.

[michael.h.f.wilkinson]

I can imagine what causes this effect: the moon filter is just an ND filter, which simply (should) scale the intensity at all wavelengths down equally. This does not enhance contrast. The "black" areas of the moon are mainly skyglow/light polutions, whereas the bright areas are dominated by the continuum of the sun. Thus, the black areas will be affected much more by an LPF than the rest of the moon, thus enhancing contrast.

[LukeSkywatcher]

Interesting Michael. Another thing i noticed was when the moon was behind thin clouds and a "halo" was visible to the naked eye around it that with the LPF the "Halo" was nowhere to be seen.

[michael.h.f.wilkinson]

That is odd. The halo is continuum (mainly) and should be visible to some extent. It may simply become too weak for the eye to catch it. Also, if you are just putting the LPF in front of your eye, the reflective surface they have may limit visibility of faint features.

[LukeSkywatcher]

No sorry. I meant the LPF was still attached to the scope and the "halo" seemed to vanish although i could still see it naked eye. That was a bit odd alright. I should have seen it because i was using a 20mm EP at the time so i had a good view of the surrounding sky. I'll have a look tonight to see if i see the same thing (or dont see it as the case is).

[michael.h.f.wilkinson]

A true halo is about 22 deg in radius. There may be a narrower glare around the moon. Is this what you saw? A 20mm EP gets you about 1.5 deg FOV at 32.5x magnification. You would not spot the halo then. Another cause could be stray light(polution) entering the tube. This would be removed effectively by the LPF.

[LukeSkywatcher]

It wasnt a true halo (hence i put "quotes" around the word). It was simply the effect you get when the moon shines from behind clouds (and highlights the clouds). I've seen a true lunar halo before (no clouds) which was quite amazing. You could be right. Maybe with the 20mm EP the magnification was too high and FOV too narrow to see it.......even though i thought it was quite close to the moon.

Thanks for that.

Sooooooooo anyone else use a LPF instead of a moon filter?

[DannyL]

I found the same thing with my skymax, mind you, I do think there was a real difference in quality between the moon filter ( plastic, bit nasty, came free with the scope) and the pollution filter I actually paid real money for. Maybe it's just that, maybe the glass quality is better. Anyway thats the one I use now.

[Astro_Baby]

I have a very dark moon filter which always gives the moon a green tinge. I also have a neutral density which is quite light. I quite often use the LPF paired with the ND for moon watching or sometimes use a green filter paired with the ND filter.

[LukeSkywatcher]

I found the same thing with my skymax, mind you, I do think there was a real difference in quality between the moon filter ( plastic, bit nasty, came free with the scope) and the pollution filter I actually paid real money for. Maybe it's just that, maybe the glass quality is better. Anyway thats the one I use now.

I have a moon filter that came with my Celestron EP kit. Judging by the price of EPs and the cost of my kit i reckon the moon filter is worth about £15. The SWLPF cost me twice that. I am just amazed that a filter designed for one purpose (LP) can be better then another filter that is designed for another purpose.

AB, i know that you use a LPF with your moon filter. That i have not tried yet. Next clear night i am gonna try it.

For the moment....i am chuffed that a LPF kills 2 birds with 1 stone...............reducing LP and acting as a moon filter at the same time.