Filters for visual use?

[pipnina]

I hear that one of the best ways to cut through light pollution for emission nebulae is with an Ha or an Olll (OLLL or Oiii?) filter. I've looked before but AFAIK the only ones I can find are for imaging. Can I use imaging filters for visual use or will I have to get different filters for that?

Another question would be: Most stars emmit all across the spectrum, so would a filter like Ha, Olll or UHC also make reflection nebulae/galaxies more easily visible? I know that stars tend to emit all across the spectrum even if they can be biased. Despite LEDs taking over where I am, the sky is still very very orange and all of these filters cut out the 580~nm sodium glow.

    ~pip

[rwilkey]

Hi Pip, the OIII and UHC filters for visual use would be the best choice, the OIII in particular if you are only buying one.  Make sure they are for visual use though, NOT for CCD.  The filters mentioned are good for most nebula, the OIII for those feint ones that are difficult to see.  Reflection nebula does not usually benefit very much from these filters although worth trying.  Centre of M42 is worth a view among others.

[cathouse42]

http://stargazerslounge.com/topic/245784-filters/

http://sas-sky.org/wp-content/uploads/2011/09/SAS-The-Use-of-Astronomical-Filters1.pdf

[pipnina]

Hi Pip, the OIII and UHC filters for visual use would be the best choice, the OIII in particular if you are only buying one.  Make sure they are for visual use though, NOT for CCD.  The filters mentioned are good for most nebula, the OIII for those feint ones that are difficult to see.  Reflection nebula does not usually benefit very much from these filters although worth trying.  Centre of M42 is worth a view among others.

I did think, when I looked at UHC, it seemed like it would probably be a good all-rounder.

I had a look at this one, wlthough the price does seem a little "Too good to be true" (in that it might perform badly in comparison to the average £30-£40) http://www.wexphotographic.com/buy-sky-watcher-1-25-inch-light-pollution-filter/p1525547What do you think?

http://stargazerslounge.com/topic/245784-filters/

http://sas-sky.org/wp-content/uploads/2011/09/SAS-The-Use-of-Astronomical-Filters1.pdf

Based off that thread, the Olll and the UHC do seem rather popular. I might opt for a UHC frst and then get an Olll later.

That page seems a decent read. Just glanced over it as of yet though.

[rwilkey]

Hi Pip, the light pollution filter (LPR) is not the same as nebula filters, which do a different more specialized job, also, don't confuse UHC and OIII with LPR filters, yes they do cut out the same wavelengths as well, but too much assimilation has been drawn on this forum in recent months and the filters themselves are very different.

[John]

For your scope I think a UHC filter would provide the best results, possibly followed by an O-III in the future.

Robin is quite correct that UHC and O-III filters are quite different from LPR / LPF type filters.

[cathouse42]

There are some differences in UHC filters out there,

I've seen UHC-S, UHC, UHC-E etc.

[John]

The UHC-S is a Baader filter aimed at smaller aperture scopes. It's band pass width is wider than other UHC filters. The UHC-E is a budget version of the UHC Astronomik filter again aimed at the owners of smaller aperture scopes. It's still somewhat more expensive than other brands "regular" UHC filters though !

The UHC filters from Explore Scientific look interesting and are relatively new players on the block. They are priced quite attractively.

[cathouse42]

Anywhere got a list of wavelength transmissions for all these major UHC filters?

[alro]

Attached

I have great results with this. £40ish new.

Al

[cathouse42]

I have a Baader UHC-S, if in doubt I generally look to Baader lol.

They're not too expensive though until you hit 2" filters.

[Stu]

This is quite a good site for filter curves. Not all of them by any means but quite a few so you can get an idea of the differences.

http://www.astrosurf.com/buil/filters/curves.htm

[cathouse42]

Is there a large difference between UHC and UHC-S transmissions, is UHC stronger/higher contrasting?

[cathouse42]

This is quite a good site for filter curves. Not all of them by any means but quite a few so you can get an idea of the differences.

http://www.astrosurf.com/buil/filters/curves.htm

So, what is the ideal transmission we should look for in UHC filters?

And what are things we DON'T want in transmission curves in UHC filters?

In other words, what is a good curve, and what is a bad curve.

[Stu]

Is that link working? Doesn't seem to be for me...

[cathouse42]

Is that link working? Doesn't seem to be for me...

Works for me.

[Stu]

Ok great.

It's not so much a case of good or bad, more what suits your purpose.

Basically most UHC filters have band passes which include the two OIII lines plus Hb. Some (such as the Astronomik) also include the Ha and SII lines.

OIII just passed the OIII doublet.

For me it's a matter of seeing how high the pass is on the frequencies you want to see, and how sharp the cut off is either side. Lumicon for instance has a nice sharp cut off and tight bandpass around the desired frequencies which helps increase the contrast of target objects.

The tighter the pass though, the less light overall is let through so sometimes this leads to too much dimming in small scopes.

Ironically I do think filters work best when your dark adaptation is good too, so you get as much of the reduced light into your eye as possible.

As an example of when the Astronomik may be more useful than the Lumicon, I believe galaxies such as M101 have strong Ha regions in them, so whilst you would not normally use a UHC filter to view galaxies, an Astronomik UHC may be useful in this instance.

You will see that the Baader UHC-S has a much wider pass around the OIII/Hb and Ha/SII lines, so let's more light through and is supposedly more suitable for smaller scopes. This will be at the expense of contrast though, and the Lumicon works well if you have dark skies and well adjusted eyes

[cathouse42]

Well, anything works best with dark adaptation lol

In fact I sit using my Red lamps now in the evening rather than the white when on the computer (yes I know the screen is blue light).

[pipnina]

Well, anything works best with dark adaptation lol

In fact I sit using my Red lamps now in the evening rather than the white when on the computer (yes I know the screen is blue light).

Well, your screen is actually a close representation of white light filtered through diffusing layers to give an even luminosity and then finally being filtered through a grid of red, green and blue liquid crystal pockets that become transparent with electrical current.

Unless you're using a CRT (old boxy screens), then it's a stream of electrons being directed by 5 magnets (1 focussing, 2 for the x axis and 2 for y) at phosphour dots on a lead glass screen. (it's lead because the electron's reaction with phosphour creates not only visible light but also x-rays, kinda important for that to not be radiating towards your face)

But yeah, blue light is included. (although a program called f.lux can reduce the blue light as day turns to night so it's nicer on your eyes. I've heard good things about it.)

[Stu]

Well, anything works best with dark adaptation lol

In fact I sit using my Red lamps now in the evening rather than the white when on the computer (yes I know the screen is blue light).

I mentioned the point because many people think filters are some form of magic bullet which overcome light pollution. To a degree they can help, an OIII can make the Veil Nebula visible under quite average skies, but under dark skies the effect is much more dramatic

Oh, and actually planetary observing is often better with non dark adapted eyes, you perceive colour more easily even if using a filter such as a neodymium.

[michael.h.f.wilkinson]

I have fairly cheap UHC and O-III filters, and they work well. I might some day upgrade to more upmarket ones like the Astronomik or Lumicon.

[Stu]

I have fairly cheap UHC and O-III filters, and they work well. I might some day upgrade to more upmarket ones like the Astronomik or Lumicon.

I think it's worth it Michael, I definitely saw an improvement moving from SW to Lumicon.

[michael.h.f.wilkinson]

I think it's worth it Michael, I definitely saw an improvement moving from SW to Lumicon.

It might well be. With the filter-switch diagonal I have, it is easy to swap them around, so testing the benefit should be straightforward. My suspicion is that the difference is not perhaps as big in terms of transmission bands, but much more in terms of optical figure. I do sometimes feel a slight degradation it pinpoint image sharpness when using the UHC and O-III with the Naglers. This could not be due to bandpass issues, but might indicate that the filter surfaces are not quite as plane parallel as they might be

[Stu]

It might well be. With the filter-switch diagonal I have, it is easy to swap them around, so testing the benefit should be straightforward. My suspicion is that the difference is not perhaps as big in terms of transmission bands, but much more in terms of optical figure. I do sometimes feel a slight degradation it pinpoint image sharpness when using the UHC and O-III with the Naglers. This could not be due to bandpass issues, but might indicate that the filter surfaces are not quite as plane parallel as they might be

I'm sure the figure is better, but I reckon the bandpass is tighter too. I never had much luck seeing the Veil from my house with the SW, but it is definitely doable with the Lumicon.

[John]

My first sighting of the Veil nebula came with a Baader UHC-S filter used with an ED100 refractor. I was thrilled to see it

I've since found that O-III filters provide quite a bit more contrast enhancement on this and similar objects but sometimes at the expense of dimming out quite a few background stars.

Other UHC type filters that I've tried which have worked well include the Orion (USA) Ultrablock and the Telescope Services (TS) UHC. The Baader O-III was not quite such a happy experience for me because it has the narrowest band pass of the O-III filters which, for me, meant loosing the background stars virtually completely. I prefer to see a deep space object in the context of some sort of star field but that may be a personal preference.

For quite a few years I found a 2" Astronomik O-III all the deep sky filter I needed in my scopes which range from 4" to 12" aperture. Relatively recently I've moved to having a UHC type filter again in the form of the Omega DGM NBP filter and complimenting that with the superb Lumicon O-III.

I did have some very nice results from the lower cost filters though so there is no need to spend a fortune on these things.