LP filter

[colesmat]

Hi folks. After two short sessions in the garden over the last 2 nights I've found that my LP filter doesn't actually do a very good job. It seems to block out more light than is needed. After getting saturn in the ep I thought I'd see how it looked with the filter in. Once in it was nigh on impossible to get focussed. Same when looking towards Leo and Ursa major. It was better seeing without the filter. What would anyone say was the problem?

Matt

[RikM]

What sort of targets were you looking for/at? LP filters don't really work too well on galaxies.

It could also be that you have the wrong filter for your local flavour of LP. Most seem to work best on sodium or mercury lamps. If you have LED lighting, you are basically stuffed, nothing will filter that out

You also need enough aperture to work with. All filters work by cutting out some of the light so the view will get dimmer. Basic LP filters don't cut out all that much though.

[swamp thing]

Hi Matt

LP filters will not make any difference to planets. Planets require good steady seeing to observe them not dark skies. You can observe planets from a city centre with no downside.

As Rik mentions the usefulness of a LP filter on Nebulae often depends more on what type of local lights you have.

[umadog]

You have to remember that:

a ) Filters work best on emission nebulae. They will make galaxies and stars worse because they cut out a fair bit of light.

b ) They reduce your maximum useful power to below about 10x per inch due to light loss. So that doesn't mean you can't use them on a smaller scope, it just means you need to restrict yourself to larger targets. So an LP filter on a smaller scope will work well for the big nebulae in Cygnus but won't help with small planetaries.

[LukeSkywatcher]

As has been sais above...........LP filters will not improve views of planets. You need good steady "seeing" conditions for that. They will also not work for observing galaxies. For that you need dark skies.

LP filters MAY work ok for observing nebs, but not very well. To really see Nebs (there are different types), you need a UHC filter and/or an Oiii filter.

A LP filter will work fine for general observing of constellations,clusters,asterisms etc.

[umadog]

Yes, it depends what you mean by a LP filter. There are plenty of different things out there going under that moniker.

[scarp15]

Light pollution filters may help gain a bit of contrast to enhance the profile of certain nebulae, at the expense of dimming sllghtly the object.

To combat light pollution, fit a dew shield, if you have a reflector then flock it, and try to create a shaded area for observing. In my yard there are bushes and trellis, each of these factors will help to block out stray light. Someone recently posted an interesting solution - using a large garden parasol to screen the light from a neigbours window. So innovate and thinking a bit lateral is key to improving your personal viewing space.

Edit no substitute for dark adapted eyes to, even though this can be quite challenging when at an urban environment.

[umadog]

Let's just be clear on one thing, though. A UHC or OIII filter can make a lot of difference on the right object. For example, the Crescent Nebula in Cygnus is invisible from a light polluted area without a filter. Add a filter and it appears quite clearly. Ditto for the North America and the Crystal Ball. The Veil nebula also reveals loads and loads of detail with a filter but can be hard to see without. Even from a completely black (think desert) location a UHC or OIII will show way more in these objects than you'd see without a filter.

As Iain says, dark adaptation is key. If you're using a filter in an environment where you have direct (line of sight) light glare then you'll need to take precautions to maintain dark adaptation. Since, as Iain says, at the same magnification the filtered view will be dimmer you will need to maintain adaptation to get the best from your filter. Furthermore, since the filter is silvered, light shining into the eyepiece can create monumental quantities of glare. Of course, the answer to the dimming question is just to use lower power. The optimal exit pupils for the popular filters are here: http://www.scopecity.com/how-to/select-telescope-filters.cfm?pn=How+to+select+telescope+filters The exit pupil for your eyepiece is eyepiece focal length divided by telescope focal ratio. This is really the key thing: use the right exit pupil for the filter and don't worry about the "your telescope is too small for a filter" thing. Just keep in mind that if you can't magnify much (remember that exit pupil decrease with magnification) the filters will only be of use for the larger objects.