Filters

[Monstar]

Hi all,

Just thinking about light pollution etc and have heard/read about LP filters but can't seem to find anywhere selling them as such. What sort of filters are they? Are they any good?

Also with the terrific M42 about again what would be a good filter for nebulae? I've heard of UHC and OIII but don't know what they (or any) filters do/are good for. Also would they work OK in my little 130p? What sort of difference would they make?

Cheers!

[astro744]

See http://www.lumicon.com/store/c/18-Filters.aspx and click on filter guide at bottom of page.

See also http://www.televue.com/engine/TV3b_page.asp?id=24#.U-m_zOOSy5I

See also http://www.astronomik.com/en/visual-filters.html

See also http://www.thousandoaksoptical.com/nebula.html

See also http://www.dgmoptics.com/DGMfilter_portal.htm

See also http://www.bintel.com.au/Accessories/Filters/48/catmenu.aspx page 2 and 3

A UHC is the most versatile and useful for emission nebulae. An O-III is excellent for planetary nebulae and for extra contrast on emission nebulae.

A H-Beta is for the elusive horsehead nebula and a few other objects. Do not buy this one first!

They are also called nebula filters.

I would recommend a UHC type filter. I prefer Lumicon but there are many good ones.

[Monstar]

Cheers for that Astro, I'll have a good read before I decide.

[Monstar]

I got up early again only to be met by total cloud cover so I thought I'd read up on some filters and the links Astro744 provided.

I think I'll go with Astro's UHC recommendation, but have also read some things that suggest a UHC-s is more suited to smaller apertures. Can anyone spread any light on this?

[OzStarGazer]

I bought the Celestron UHC/LPR filter and it works fine with our dob. The sky is darker, and the other day for example I looked at the Orion nebula and it was very clear. Of course the stars will be dimmer too though, and those that were barely visible without a filter will possibly not be visible any more.

[Monstar]

Where did you pick that up from OSG, if off ebay how much?

[mental4astro]

YES!!!!

Remember, filters act by cutting out light we don't want. UHC and OIII let a very small amount of light through to restrict it to a very specific bandwidth. These bandwidths are very narrow and on the most part to an area where our eyes are not great in when light levels are low. These filters are then better suited to LARGER apertures as they gather more light to make these filters effective. They do work with small apertures, but smaller apertures render an image that is dim to be really effective.

If you have a small aperture, you require a wider bandwidth through put. Something like the Lumicon Deep Sky filter. These are very good filters to use in the big smoke with novices as they allow more light through. It is a good first filter.

Look carefully through the Lumicon filter selection guide. It explains what each filter does and what they are best for. Astro744 mentioned this guide first but it requires you to click on a poorly marked link:

http://www.lumicon.com/pdf/3filterspec_prnt.pdf

Now, there is another problem with filters, in the way they are marketed. As there is no universal standard on nomenclature, some filters are not what they are labelled as being. The Celestron one mentioned & the Baader UHC-s are not true UHC type. They work, but the band through-put is more of a wide band Light Pollution Filter. You will not see the Horse Head Nebula with this Celestron or Baader filter, where with a true UHC type you will (using a minimum aperture of 8" too). The objects that make the most out of UHC filters are very dim from the first instance, like the Horsie. True UHC type work very well with brighter objects, but their main purpose is to detect these very faint objects.

There are are also hybrid filters that cross over different bandwidths. Omega Optical, the parent company of DGM, make an OIII + Hbeta filter that for me is probably the best all round filter if you only want to purchase the one filter. Not only is it effective in the OIII range, but it also allows the Hbeta to be transmitted where the Horsie nebula glows in. Yes the overall image is a little brighter than a native UHC or OIII, but it is a great compromise. I've seen the Horse Head Nebula with this filter too, which you won't see in a dedicated OIII filter. You'll find this filter on the Omega Optical's ebay site:

http://www.ebay.com.au/itm/Filter-486-Astronomy-Hb-OIII-Nebula-II-28mm-1-25-/350238144653?pt=Educational_Toys_US&hash=item518bd1f88d&_uhb=1

Omega Optical makes the filters for some high profile brands - you just won't hear about it too much. They make their own prestige line of filters under the DGM banner. Having two outlets, and their own manufacturing facilities, they can be very creative with the filters they produce. Their UHC type filter called the NPB, is considered to be as good as it gets for this type of filter. Their OIII is flaming brilliant too. But, puritans just can't swallow hybrid filters, so the OIII+Hb filter is marketed under the parent company's brand.

I also have an NPB filter. It is terrific. But I still use the OIII+Hb filter a whole lot more...

[mental4astro]

There is another good filter guide written by fellow IISer ausastronomer:

http://www.iceinspace.com.au/63-680-0-0-1-0.html

[rrussell1962]

Monstar, I think I have a spare 1.25 inch broadband light pollution filter that I no longer need. If you want it PM me. I am in Brisbane West.

Richard

[OzStarGazer]

I bought it from AgenaAstro on eBay for about $96 incl. shipping.

[Monstar]

Hi Russell,

pm sent!

[rrussell1962]

PM back - freebie to good home!

[mental4astro]

What a gentleman! :thumbsup: :)

[Renato1]

I'm not sure what a 130p is. If it means it is 130mm diameter, and you want a UHC filter for it, I'd recommend either the Kson UHC or Astronomic E UHC filter.

The more typical UHC and Ultrablock filter will work in a 130mm telescope, but the images will be dimmer as they are meant for 8" or larger telescopes.

You'll have fun comparing the views in a UHC to your broadband filter. They are both useful.
Regards,
Renato

[ausastronomer]

A very generous gesture. Give yourself a pat on the back

Cheers
John B

[rrussell1962]

Oh-just need to pay back all the generosity and time I have had from people over the years. Alexander, yours included, John, yours also via your posts which I have always read with interest.

R

[Monstar]

Yes indeed, the generous offer is very much appreciated.

[Don Pensack]

Here is a guide to filters, which includes the so-called "light pollution" filters (aka broadband filters). It might help clarify what the filters are for, and in which scopes they work.
http://www.eyepiecesetc.com/Choosing_a_Nebula_Filter_p/nebula-filters-explained.htm And see "Extended Info" tab for the text.
Feel free to cut and paste at will.

Note: despite what you may have heard, if the purpose of one of these filters is to enhance the nebulae, dimming the stars and background sky in the field, while making the overall field darker, will not dim the nebulae and will only serve to make them stand out from the background more.
Hence, there is no minimum aperture for any nebula filter, but there may be an "aesthetic" preference to see more stars with a wider bandwidth. This, however nice it may be, will reduce the contrast for the nebula, however.
Ergo, the filters known as "broadband" or "LPR" filters are only desirable to use when you are already under very dark skies and just want the contrast turned up a tiny bit. But, even under dark skies, when you want to see the nebula better, it's going to be a narrowband or line filter.

[Monstar]

Hey Don,

This is why I decided to not take up the freebie offer and I'm going with a UHC filter instead (there's no point in me taking up the generous offer just for the sake of it).

I've never used a filter before but want one to enhance viewing of emission nebulae. I know I won't see them as they appear in the great images on this and other sites, but I want one to increase detail. I've only been reading up on filters a few days and my reasoning for choosing a UHC is that although stars may disappear and the overall image be dimmer, the contrast between the background and the viewed nebula will be greater, so enabling better detail to be picked up in the nebula itself.

As a beginner have I got this correct, is there a better option, or am I barking in the wrong park.

[Don Pensack]

The TeleVue O-III, however, does not transmit the H-Beta line in the spectrum.
My recommendations for a good narrowband are:
1st group
Lumicon UHC
Orion Ultrablock
DGM NPB
Thousand Oaks LP-2
2nd group (passable, but a little less contrast)
Andover 3ch Nebula filter
Meade 908N (used only)
Telescope Service UHC
TeleVue Nebustar