Is a light pollution filter or UHC filter better

[beamer3.6m]

Title of the thread says it all.

I intend to do widefield shots and what to reduce light pollution and increase ability to see nebula like the fainter bits around M42.

[beamer3.6m]

Any ideas on what is best.

My understanding is that the UHC combats light pollution also so would be a better bet financially. However I have also now seen the OIII filter.

This is suggested for dark skies but I want to attach it on front of my standard camera lens for long exposures from generally light polluted skies (I live in standard road with the usual street lights etc but not a city).

I am very confused by the filters and they are so expensive I do not want o make a mistake.

[SteveA]

I think basically you could sumarise and say;

A UHC filter is normally intended as an aid to visual work...not really intended for imaging..

An LP filter attempts to block the wavelengths of light in the part of the spectrum most normally associated with street lights eg..mercury vapour lamps...so can be effective in imaging

The OIII, Ha etc filters are known as "narrow band" filters, used almost exclusively for imaging, they are more expensive than the LP filters and transmit only a very narrow band of the spectrum. They tend to be used with mono CCD cameras, require longer imaging runs....they obviously also block the LP...but that's not really why they are used..

So depends which camera you are intending to image with........

I'm no expert only having tried imaging in Ha.....so you will likely get some better responces here!

[beamer3.6m]

That all makes sense.

In terms of my camera it is a standard (not modded) Canon 400d with a standard lens. Long exposure is not a problem as I piggyback on the back of my 200p/HEQ5 etc.

5 - 10 minutes are fine.

My aim is to reduce light pollution and also bring out the detail in nebula, such as the veil, albeit at widefield.

[RogerTheDodger]

IMHO an LP filter would be more what you are looking for.

[GlassWalker]

Very generally you need to consider in part what your target subjects emit.

LP filters attempt to block the common types of light pollution (sodium, mercury) while passing as much of everything else as possible. Good for improving all deep sky objects if light pollution isn't too bad.

UHC passes a band around OIII and H-beta, where the eye is sensitive. It can also pass reds including H-alpha depending on the filter. May be better for emission nebula in heavier light polluted areas, but possibly worse for broad spectrum objects.

Narrowband filters like OIII or H-alpha are only really useful on emission nebula, but will give the best rejection of other light. Not ideal for use on a colour sensor since the majority of it will be ineffective, but it can be a sacrifice worth making in heavily light polluted areas.

Depending on the optics used, the sensor and the filter, you may also need to consider IR contamination effects. An unmodified DSLR isn't very sensitive to IR but it may be a consideration if you're thinking of modifying in the future. For example Astronomik do regular and "CCD" versions of their filters. The CCD version includes IR blocking, where the standard ones don't. I got their regular CLS filter, which was fine until I modified the body... doh!