Janet & Dahlia,

I have Orion's versions of the light polution filters (both the broadband
'Skyglow' and narrowband 'Ultrablock'), and they work pretty well for the
specific bandpasses that you comment on. I did have a few thoughts as to
your poor experience (Janet) with the Meade broadband filter.

If you are viewing from a heavily light polluted city loation, your are
getting pollution from sources that are not blocked by the filter, thus some
light pollution is reduced (sodium, mercury), but the rest can still be
enough to spoil your view.

Also, you mention that the filter 'darkens your view'. This is to be
expected, after all it is a filter and is keeping some light from entering
your view. The specific bandpasses allowed by the filter should remain
mostly (mostly...) unaffected, but all others will be dramaticaly reduced or
negated completely. This is what is wanted when looking at a specific
nebula for example, because the filter should pass most (most...) of the
light of the nebula, but little other light. The end result is that the
nebula is slightly dimmer than usual, but appears easier to see because the
rest of the light in the view is lessened quite a bit more by the blocking
action of the filter, giving you better contrast on the object and allowing
you to see more detail.

This action is why these types of filters (both broadband and narrowband)
are pretty much useless when looking at the galaxies, clusters, and doubles
that you mention, Janet. Stellar light is quite a wide range of the
spectrum, and much of it is blocked by the filter. The specific bandpass
filters such as the OIII, H-alpha/beta, SII, and others of a similar type,
all work on the same principles and will fail miserably when looking at the
'wrong' objects, but will perform amazingly when looking at the 'right'
ones.

The broader the filter's bandpass, the less dramatic these right and wrong
results are going to be.

Anthony J. Kroes
Green Bay, WI

> -----Original Message-----
> Janet L Miller
> Sent: Monday, June 18, 2001 2:09 PM
> Subject: [M]: Re: Re: Light Pollution/Nebular filters
>
>
> Hi Dahlia,
>
> I have a Meade 1.25 broadband fliter. In my light polluted back yard, it's
> pretty much worthless. It does what it claims to do, filter out
> mercury and
> sodium vapor light, but it also darkens your view as well. It
> seemed to work
> better at my dark site than it does in a light polluted area.
> Bright nebula
> are the only objects it seems help on - with galaxies, clusters
> and doubles
> it's more of a disadvantage in my opinion. I believe I spent about $80 for
> it, money that could have been spent for an EP or some other usefull item.
>
> I'd repeat the earlier post, and opt for a OIII or narrowband filter,
> depending on your needs.
>
> I can't comment on other brands of broadband filters, the Meade broadband
> is the only one I've used.
>
> ----- Original Message -----
> Sent: Monday, June 18, 2001 4:05 PM
> Subject: [M]: Re: Light Pollution/Nebular filters
>
>
> > Hi,
> >
> > As someone stuck in a light-polluted observing site--I've also been
> thinking
> > of a broadband filter. Don't know much, but you might want to
> check into
> > availability before ordering. Last I checked, the Meade
> broadband filter
> is
> > back-ordered about 6 months from the mfctr.
> >
> > Dahlia
> >
> >
> >
> >
>
>

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