Light pollution filters on a 5 inch scope

[Staffy]

My prime observing spot (my balcony) suffers considerably from light pollution. When I mentioned this at my local astronomy shop I was told it wasn't really worth buying a pollution filter for a scope of less than 6 inch diameter. I'd love to give one a try but don't want to waste my money if it's not going to do any good. My telescope is 130mm (5 inch) reflector. Any thoughts?

[jgs001]

I've never used one for visual with my 80mm refractors, but do all the time for imaging. I can't say, one way or the other, if it's worth it for visual, sorry.

[oldfruit]

Hi, if you dont want to risk spending a lot of money you could always go for a second hand filter. They sometimes go quite cheap on ebay.

[sixela]

Wrong advice. You do have to select the objects carefully when you use the filters as they're usually best at low-to-medium magnification, but I've held H-beta filters in fron ot toilet rolls and an eye (6mm aperture) to observe Barnard's loop. I use the whole range of filters (GCE, Lumicon Deep-sky, UHC/NPB, H-beta) on my 114mm Starblast too.

So that advice frequently comes because of people who try to magnify a lot on small scopes and then use filters. But for objects like NGC7000, the Rosetta nebula, M42 etc. you can use filters in small scopes as well.

If you get one filter, get a good UHC filter (Lumicon or Omega Optical NPB). If you're also interested in smaller objects and still want to filter, Lumicon Deepsky or Omega Optical GCE.

UHC filters, by the way, are fairly useless for galaxies and clusters, but they're extremely effective for emission nebulae. For galaxies, get the GCE or Deepsky (buth they'll only help moderately) and for clusters magnify more than you would at a dark site (that trick also helps on bright planetary nebulae and small but galaxies with high surface brightness).

[russ]

As an alternative to the filters Sixela recommends, consider the Orion Skyglow equivalent. There's been a couple reviews that put the Orion on a par or a tad better but at almost half the cost (£47 vs £87).

Some links for you:

Orion SKYGLOW Broad-band Light Pollution Filter - CN Report

Lumicon Light Pollution Redcution filters

Useful Filters for Viewing Deep-Sky Objects - Review

Filters - SCS Astro

[Staffy]

Sounds like a trip to the shops is in order! Thank you all for your valuable advice. It is much appreciated

[LukeSkywatcher]

My Skywatcher LPF works great with my 5" scope. You can buy them from FLO for about £30.

[sixela]

As an alternative to the filters Sixela recommends, consider the Orion Skyglow equivalent.

Orion Skyglow is equivalent to a Lumicon Deep-Sky, but the Lumicon UHC is equivalent to the Orion Ultrablock.

If I had one filter I'd pick the more aggressive of the two. It does help less objects (emission nebulae only) but it makes much more of a difference.

[Wurzil]

I find my skywatcher LPR filter does very little for me on my 120mm scope (i have moderate light pollution). I think the cheap ones like the skywatcher are supposed to work best if you have a lot of the yellow streetlights around - my area has the new off-white coloured ones which is probably why my lpr filter stays firmly screwed to the bottom of a kellner EP that i never use. The only time ive ever found it useful is when ive been trying to calm down Venus!!

I am considering trying out a uhc filter for m42 etc, so thanks for your comments alexis.

w

[LukeSkywatcher]

I have a SW LPF (£30). I can point it directly across my street between 2 old yellow street lights and you would not even know they are there.

[umadog]

The UHC filter does dim the object under study substantially. This means you'll have to user lower powers in whatever scope it's attached to. If memory serves, a value of about 5 to 10 x per inch is recommended with UHC and OIII filters. Certainly that tallies with what I experience with my 12". I generally find these filters most useful below 150x; 80x works well. The dimming of the object also means that to get the most out of the filters you need to get (and stay) well dark adapted.

I would guess (no experience with 5") that with a 5" scope these filters will be most useful only for larger nebulae which require powers under 50x (10x per inch). Planetary nebulae often require more power and in a 5" will appear too dim if you combine higher power with a filter. For small bright objects you may get more benefit simply by using higher power on its own to darken the sky background. My experience has been that the OIII and UHC are much more useful in my 12" then my 8" since they remain useful at 80x to 150x (possibly even a little higher for some objects) which are commonly use DSO magnifications for me. With the 8" I tended to ran out of light at around 80x, a common DSO power with my 8", so it was never clear to me if the view was better with or without the filter.

Still, the filters are a good investment and you will find a use for them even at 5". Of course you can keep them when you upgrade scopes. I recommend buying a 2" filter and getting a 2" to 1.25" adapter which is threaded for filters. That way you 2" filter works in all your eyepieces. Look around the second hand market. I bought a slightly damaged 2" OIII for $40, so bargains are out there.

Also see:

Filter Performance Comparisons - Article

Useful Filters for Viewing Deep-Sky Objects - Review