Light Pollution

What's a good place to get a light pollution filter for my scope?
Explorer 130m with 1.25" fitting.
Also, It has been reccommended that I get a better Barlow lens - is
there a disadvantage in getting a higher power than the 2X that was
supplied?

What's a good place to get a light pollution filter for my scope?
Explorer 130m with 1.25" fitting.
Also, It has been reccommended that I get a better Barlow lens - is
there a disadvantage in getting a higher power than the 2X that was
supplied?

There are different kinds of light pollution filters. Roughly they fall into
three categories:

(1) Broadband: eliminate some of the light.

(2) Narrowband: eliminate a lot of the light but also dim objects more. Both
are best with emission nebula and older low-pressure lighting.

(3) bandpass: OIII, Ha etc. These pass just a specific very narrow range.
They can really darken the sky while not taking very much off of emission
nebula. You do need to be careful to let your eyes dark adapt.

As a very general rule of thumb, the more restriction, the bigger your scope
needs to be. That makes sense when you remember your filter is going to stop
a lot of light, so you need more light at the start.

I'd recommend finding a local astro club and going to a public night. You
can probably try several filters and see what you like. It depends on your
scope as well as the type of light pollution and what objects you want to
observe.

Ditto for the barlow. Wait until you have some observing time and find out
what eyepieces/magnification you are going to end up using the most.

Clear Skies

Chuck Taylor
Do you observe the moon?
Try the Lunar Observing Group
http://groups.yahoo.com/group/lunar-observing/
Lunar Picture of the Day http://www.lpod.org/
************************************

In message , CLT
writes
What's a good place to get a light pollution filter for my scope?
Explorer 130m with 1.25" fitting.
Also, It has been reccommended that I get a better Barlow lens - is
there a disadvantage in getting a higher power than the 2X that was
supplied?

There are different kinds of light pollution filters. Roughly they fall into
three categories:

(1) Broadband: eliminate some of the light.

There is a new (actually very old) subset of broadband specific to
eliminating low pressure sodium light. Baader Neodymium and my own Nonad
photographic filter being examples of the notch reject filter.

http://www.nezumi.demon.co.uk/nonad/nonad.htm

It has the advantage that exposure times are not significantly
increased. Sky fog is greatly attenuated and the sky remains roughly a
neutral grey.

I would not recommend that anyone buys a broadband LPR filter as their
first choice for visual observation. Photographically they can be good.
But be aware that US brands are optimised for use against mercury light
pollution.

(2) Narrowband: eliminate a lot of the light but also dim objects more. Both
are best with emission nebula and older low-pressure lighting.

Narrowband filters are more like bandpass filters than you imply. They
block almost everything except nebula emission lines. Lumicon UHC and
Orion (US) Ultrablock being good examples - I prefer the latter.

In between is the Orion (UK) Sodium light filter which manages to do a
pretty good job of blocking most output from low pressure and high
pressure sodium lights and is relatively cheap compared to famous
brands. It is like a highly efficient Wratten 44 cyan filter so passes
nebula emissions. Surface looks metallic gold colour. Probably the best
buy for a first filter in the UK/Europe if you are surrounded by sodium
lights.

(3) bandpass: OIII, Ha etc. These pass just a specific very narrow range.
They can really darken the sky while not taking very much off of emission
nebula. You do need to be careful to let your eyes dark adapt.

As a very general rule of thumb, the more restriction, the bigger your scope
needs to be. That makes sense when you remember your filter is going to stop
a lot of light, so you need more light at the start.

I'd recommend finding a local astro club and going to a public night. You
can probably try several filters and see what you like.

Good advice.

Ditto for the barlow. Wait until you have some observing time and find out
what eyepieces/magnification you are going to end up using the most.

The Barlow can probably wait. Magnification isn't everything.
A nice zoom eyepiece might anyway be better value for money.

Regards,
--
Martin Brown