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I need a Primer on Filters

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#1 petrus45

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Posted 15 January 2013 - 11:21 AM

I would like a primer on what kinds of filters are best for purely visual observation with regard to:

1. Light polluted city viewing in general
2. Nebulas
3. Galaxies
4. Jupiter
5. Saturn

Also, are there filters that are better in 2" as opposed to 1.25"?

So far I just have a 1.25" Ultrablock. It helps see Orion, but tends to dim most other things. It also makes everything green. Any suggestions on how to use this filter better?

Thanks!

#2 neotesla

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Posted 15 January 2013 - 11:32 AM

Look through the articles section, and here is a good one that gets posted fairly frequently...

http://www.cloudynig....php?item_id=63

#3 neotesla

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Posted 15 January 2013 - 11:33 AM

another...

http://www.cloudynig...hp?item_id=1520

#4 neotesla

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Posted 15 January 2013 - 11:34 AM

http://www.cloudynig...hp?item_id=2389

#5 neotesla

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Posted 15 January 2013 - 11:36 AM

Review section for filters...

http://www.cloudynig...ry_id=42&pr=2x9

#6 panhard

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Posted 15 January 2013 - 11:41 AM

Great links! :bow:

#7 Tony Flanders

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Posted 15 January 2013 - 01:32 PM

I would like a primer on what kinds of filters are best for purely visual observation with regard to:

1. Light polluted city viewing in general
2. Nebulas
3. Galaxies
4. Jupiter
5. Saturn

Also, are there filters that are better in 2" as opposed to 1.25"?

So far I just have a 1.25" Ultrablock. It helps see Orion, but tends to dim most other things. It also makes everything green.


I'd say you're done; you can stop worrying about filters for the next few years.

No filter helps a lot for general viewing and for galaxies, and many people would argue that no filter helps even one little bit. Galaxies are almost always viewed unfiltered.

Various colored filters can improve the visibility of subtle details on Jupiter and on Saturn's disk. But the improvement is slight and the aesthetic loss due to unnatural color is very large. So for the most part, only true hard-core planetary specialists use filters; the overwhelming majority of us view the planets unfiltered.

As you discovered with M42, narrowband filters can indeed help with certain kinds of nebulas. The improvement is modest for M42, but it's very big indeed for some, such as the Veil. But that's all they do. Yes, they make everything else dimmer, and yes, they make bright stars green.

#8 TexasRed

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Posted 15 January 2013 - 01:43 PM

Your ultrablock is probably the single most useful filter you could have. It will improve the contrast on more faint nebula than any other. Remember that no filter can add light. They can only block unwanted light that might be obscuring faint details.

#9 David Knisely

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Posted 15 January 2013 - 03:05 PM

I would like a primer on what kinds of filters are best for purely visual observation with regard to:

1. Light polluted city viewing in general
2. Nebulas
3. Galaxies
4. Jupiter
5. Saturn

Also, are there filters that are better in 2" as opposed to 1.25"?

So far I just have a 1.25" Ultrablock. It helps see Orion, but tends to dim most other things. It also makes everything green. Any suggestions on how to use this filter better?

Thanks!


For a full article on filters, check out the following:

Filters for Deep-sky Use

In brief:

1. Light Pollution filters: there really is not a good general filter that will get rid of or significantly reduce a lot of the skyglow for all objects. The broad-band "Light Pollution Reduction" (LPR) filters can help a little with some mild skyglow, but the improvement they provide is slight and they quickly saturate under heavier light pollution. Examples of these are the Lumicon Deep-sky or Orion Skyglow. They are more useful for astro-imaging than visual observation, although I do find that they can help under slight skyglow at certain powers.

2. Nebulas: Nebula filters *can* often provide a significant boost in contrast, but they won't make the objects brighter. They come in two classifications: narrow-band, and line. Your Orion Ultrablock is a narrow-band nebula filter, and is a good choice for a "all-around" nebula filter. Like most narrow-band filters, it will make M42 appear more greenish in color, but at the same time, it will enhance the visibility of the fainter outlying structures of the nebula. Use it at low to moderate powers (3.5x per inch of aperture to 9.9x per inch of aperture) under a dark sky and it should make faint nebulae easier to see. There are also the even narrower Oxygen III (OIII) and Hydrogen-Beta (H-Beta) line filters which for some specific objects can provide even more contrast. However, you have to be fully dark adapted (20 to 30 minutes in total darkness with *no* nearby lighting), use averted vision, and use the right power ranges to get the most out of these filters. They won't work miracles, but they can help most emission nebulae. They also do not work well on objects like galaxies or star clusters.

3. Galaxies: No filter will provide a lot of improvement on galaxies. There are a few broad-band LPR filters (DGM Optics GCE filter, Lumicon Deep-sky, Orion Skyglow, etc.) that may provide a slight increase in contrast for some of the larger and more diffuse galaxies, but only under mild light pollution or under a dark sky. For galaxies, the best thing to do is observe them as far away from city lights as possible and with no moon in the sky.

4. Jupiter and Saturn. A pale blue filter (Wratten #82a) can help a little with making the belts stand out, but the improvement is often minimal at best. Some people also use a yellow filter sometimes, but again, in my observations, it doesn't help very much. There are a few "minus violet" filters that help a little with simple achromatic refractors, but beyond that, for the planets, I don't use any filtration at all. The only exceptions are for Mars during a good opposition, when I use a red filter to help bring out the dark markings or a pale blue filter to enhance the orographic clouds and polar caps of the planet.

As for 2" vs 1.25", for viewing larger emission nebulae, I do like having the 2" filters for use on my wide-field eyepieces that have 2" barrels. They may be a good investment for future use. Clear skies to you.

#10 oldtimer

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Posted 15 January 2013 - 05:51 PM

It would also help to know what kind and focal length scope you are using.

#11 newtoskies

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Posted 15 January 2013 - 08:11 PM

I was thinking of ordering a filter or two...but I think now I would rather invest in better ep's. Great links btw.

#12 kfiscus

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Posted 15 January 2013 - 08:44 PM

Better EPs can be a good move but it never ends...

A good light pollution filter and a good OIII can really bring incredible new detail to your favorite objects. And they'll continue to work with whatever EPs you have, not needing improved upon like EP designs.

#13 newtoskies

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Posted 15 January 2013 - 09:40 PM

The ep's I have now are what come with scopes so I just wanted some wide field ep's of better quality.

#14 petrus45

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Posted 15 January 2013 - 10:54 PM

Awesome advice!

#15 Tony Flanders

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Posted 16 January 2013 - 05:41 AM

The ep's I have now are what come with scopes so I just wanted some wide field ep's of better quality.


I suspect that the Orion Sirius Plossl line has included various different eyepieces under the same name over the years. But in my experience, these are really quite good eyepieces. You can get better image quality, but only marginally better, and typically for a lot more money.

Wide field is a whole 'nother question -- that's a different dimension from optical quality. Some people find that it makes a huge difference, others not.

But I would say that with three Plossls in 32, 25, and 10 mm, plus a 2X Barlow, you really have a mighty capable eyepiece collection.

If it was me, I'd buy a narrowband filter before investing in more eyepieces. It's true that it's only useful for a fairly small number of objects. But for those objects, it can make a really big difference.

#16 newtoskies

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Posted 16 January 2013 - 08:31 AM

Thanks Tony for clearing things up. The ep's I have are good, but it doesn't hurt to have others. I don't want to replace my ep's , but rather add to them to fill the 10-25mm gap.I say I don't or won't get a filter...but I keep going and looking at them. The Zhumell OIII has caught my eye, but mainly because of the price.

#17 David Knisely

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Posted 16 January 2013 - 10:59 AM

Thanks Tony for clearing things up. The ep's I have are good, but it doesn't hurt to have others. I don't want to replace my ep's , but rather add to them to fill the 10-25mm gap.I say I don't or won't get a filter...but I keep going and looking at them. The Zhumell OIII has caught my eye, but mainly because of the price.


With the Zhumell OIII, you kind of get what you pay for. The Zhumell OIII was reviewed here on Cloudynights and the passband quality isn't quite as good as that of filters like the Lumicon OIII or Thousand Oaks OIII filters. I would probably pass on the Zhumell and go with a better filter like the Lumicon OIII. Clear skies to you.

#18 Tony Flanders

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Posted 16 January 2013 - 10:59 AM

I don't want to replace my ep's , but rather add to them to fill the 10-25mm gap.


Your 32-mm with a Barlow falls precisely in the middle of that gap.

Mind you, I'm not saying you shouldn't buy more eyepieces; it would surely be money well spent. Among other things, many people (including me) find the eye relief on a 10-mm Plossl annoyingly tight. But it doesn't sound urgent.

#19 David Knisely

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Posted 16 January 2013 - 11:13 AM

Tony Flanders wrote:

If it was me, I'd buy a narrowband filter before investing in more eyepieces. It's true that it's only useful for a fairly small number of objects. But for those objects, it can make a really big difference.


Uh, I think your idea of 'fairly small' and mine are quite different. I have found at least 95 emission and planetary nebulae which a narrow-band nebula filter will be useful in observing, which is comparable to the number of globular clusters easily visible to an amateur in the northern hemisphere using a small to moderate aperture telescope. Clear skies to you.

#20 Tony Flanders

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Posted 16 January 2013 - 03:25 PM

If it was me, I'd buy a narrowband filter before investing in more eyepieces. It's true that it's only useful for a fairly small number of objects. But for those objects, it can make a really big difference.


Uh, I think your idea of 'fairly small' and mine are quite different. I have found at least 95 emission and planetary nebulae which a narrow-band nebula filter will be useful in observing, which is comparable to the number of globular clusters easily visible to an amateur in the northern hemisphere using a small to moderate aperture telescope. Clear skies to you.


But dwarfed by the number of galaxies visible in such scopes.

There's no point in arguing about words. We can both agree that whether you call the number of these nebulas few or many, they included some of the most beautiful and fascinating objects in the entire sky.

#21 petrus45

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Posted 16 January 2013 - 07:54 PM

It would also help to know what kind and focal length scope you are using.


z10 Dob, 1250mm. Light gathering capability is good, but I gather a lot of street lighting.

#22 petrus45

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Posted 18 January 2013 - 02:37 PM

[quote name="David Knisely"][quote] Your Orion Ultrablock is a narrow-band nebula filter, and is a good choice for a "all-around" nebula filter. Like most narrow-band filters, it will make M42 appear more greenish in color, but at the same time, it will enhance the visibility of the fainter outlying structures of the nebula. [/quote]

David: Do the other two narrow band filters you recommend(Lumicon UHC or DGM NPB) provide more "natural" looking colors, i.e. less green, in visual observation? Or would they be pretty much comparable as to color?

#23 David Knisely

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Posted 19 January 2013 - 04:52 AM

Your Orion Ultrablock is a narrow-band nebula filter, and is a good choice for a "all-around" nebula filter. Like most narrow-band filters, it will make M42 appear more greenish in color, but at the same time, it will enhance the visibility of the fainter outlying structures of the nebula.


David: Do the other two narrow band filters you recommend(Lumicon UHC or DGM NPB) provide more "natural" looking colors, i.e. less green, in visual observation? Or would they be pretty much comparable as to color?


Most narrow-band filters do tend to make M42 look a bluish-green color. The Lumicon UHC's M42 coloration will be similar to that of the Orion Ultrablock with maybe just a bit less greenish "saturation". The DGM Optics NPB will make M42 more of a pale bluish color with a bluish-green core in the area around the Trapezium. In larger apertures, the NPB's red secondary passband may also allow some people with sufficient red sensitivity in their vision to see some faint reds in M42 as well. The color balance of the NPB is slightly more neutral than that of the Lumicon UHC, but again, in most cases, color is not the point of having these filters. The key is what they reveal, and in many cases, the nebulae are too faint to show any color in the first place. These narrow-band nebula filters all help boost the contrast of emission nebulae well beyond what is seen without a filter. Clear skies to you.






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