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Want to learn about filters

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#1 aeajr

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Posted 21 September 2015 - 02:52 PM

I now have 2 sets of binoculars, an 80mm refractor and an 8" Dob, all listed in my signature.  I have enough eyepieces for now and two barlows.   

 

Time to learn about filters.  Some of these things get pretty expensive.

 

Just on a whim I picked up 3 filters:

 

Solar filter for the ETX 80
http://www.amazon.co...ailpage_o02_s01

 

GoSky Light pollution filter
http://www.amazon.co...00YS9PAZ4?psc=1

 

25% moon filter for the ETX 80 but naturally it will work with the Dob too
http://www.amazon.co...ailpage_o01_s00

 

I have not used any of them yet.   But I realized it is time to learn a little about filters.   When and where should I use them?  What would you recommend as learning resources?

 

What wisdom would you share with a newbie?  I live in a fairly light polluted area.  I estimate Bortel 7, for what it is worth.  Naturally I want to look at planets, stars, and DSO as well as anything else that one can see in the night sky.

 

Suggestions on priorities as I am not going to run out and buy $1000 in filters right away.

 

Any really bad brands? 

 

What about buying used?

 

What about filter sets?

So, what should I know about filters?


Edited by aeajr, 21 September 2015 - 02:54 PM.

 

#2 Starman1

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Posted 21 September 2015 - 03:10 PM

Bad brands?  Yes, there are a few.

Resources to learn?  

http://www.prairieas...common-nebulae/

http://freescruz.com...bulaFilters.htm

A complete set, in my opinion, could be:

Yellow filter (Mercury, Moon, Mars dust storms, Saturn's rings)

red filter (Mars dark markings)

blue filter (Venus, Mars ice caps/clouds, Jupiter, Saturn's disc)

moon filter (to reduce brightness at low power or gibbous phase)

narrowband filter (for all emission nebulae)

O-III filter (planetary nebulae, some emission types)

Sets almost never contain the right filters.

Filters are not useful to view:

--asteroids

--carbon stars

--star clusters

--globular clusters

--reflection nebulae

--dark nebulae

--galaxies

--stars


 

#3 Brian Carter

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Posted 21 September 2015 - 03:14 PM

For your 8", I think you would really like a good narrowband filter. Rather than blocking light pollution (a mostly marketing use), think of it as only allowing certain wavelengths of light through. These wavelengths correspond to the emission of many nebula. These filters are not gimmicks, they are extremely useful on certain objects, in dark and light polluted skies.

The two most useful are the Narrowband "UHC" types and the OIII Line filter. The narrowband is a good all around filter, great for all the big bright nebulae. The OIII is very narrow, and is perfect for planetary nebulae and certain parts of others.

As far as brands: for the UHC type, stick with the Orion Ultrablock, Lumicon UHC, or DGM NPB filters. For the OIII, I like Lumicon the best.

More details about these filters and how to use them can be found by googling David Knisey, a frequent contributor here. His descriptions and guides are the best advice you c an get.
 

#4 kfiscus

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Posted 21 September 2015 - 04:15 PM

They are very expensive but good nebula filters are worth the price. Read reviews of well-liked filters and buy those used from well-rated CN or Astromart users. You can "flip" the ones you don't like for even money.

To get your money's worth, invest in a filter slide when you have a few filters. A filter slide makes it easy, safe, and quick to use your filters.

Edited by kfiscus, 21 September 2015 - 04:19 PM.

 

#5 havasman

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Posted 21 September 2015 - 04:43 PM

As far as brands: for the UHC type, stick with the Orion Ultrablock, Lumicon UHC, or DGM NPB filters. For the OIII, I like Lumicon the best.

More details about these filters and how to use them can be found by googling David Knisey, a frequent contributor here. His descriptions and guides are the best advice you c an get.

Based on my single session experience with the Starguy UHC, it can also be recommended. It seems a bit broader than the Lumicon UHC, but is plenty effective on M8, M20 and the lesser nebulae in the immediate vicinity, showing them brightly. [My mid-2015 vintage DGM NPB arrived today & I'll try comparing the 3 ASAP.]

 

I have quite a bit of time in with the Thousand Oaks O-III and it's very good from dark skies.

 

+1 for reading David Knisey on the subject.


 

#6 penguinx64

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Posted 21 September 2015 - 05:08 PM

I'm curious to see your review of the GoSky filter. I considered one of those too. If the 25% ND moon filter isn't dark enough, you could try stacking the GoSky with it. The GoSky filter could improve the view of Jupiter too. But filters are one more thing to fumble with in the dark.
 

#7 Starman1

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Posted 21 September 2015 - 05:19 PM

I wonder who GoSky is.


 

#8 Brian Carter

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Posted 21 September 2015 - 05:44 PM

I'm curious to see your review of the GoSky filter. I considered one of those too. If the 25% ND moon filter isn't dark enough, you could try stacking the GoSky with it. The GoSky filter could improve the view of Jupiter too. But filters are one more thing to fumble with in the dark.


That's why you invest in a filter slide/wheel, one of my better and least expensive upgrades. No more fumbling, just click it in and out of place. Very useful for finding those tiny planetary nebulae.
 

#9 Starman1

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Posted 21 September 2015 - 06:08 PM

http://www.lumicon.c...-Selectors.aspx

always call first to check stock.


 

#10 Brian Carter

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Posted 21 September 2015 - 06:23 PM

Oh my gosh those are expensive! Also check out Astro Crumb and Moonlite. I especially like the moonlite of you have one of their focused. But the astrocrumb is why I have now and it works great, even screws onto the nosepiece of my Feathertouch. Less expensive than Lumicon, although theirs looks like it would be really nice.
 

#11 ron2k_1

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Posted 21 September 2015 - 07:44 PM

http://www.lumicon.c...-Selectors.aspx

always call first to check stock.

 

 

Oh my gosh those are expensive! Also check out Astro Crumb and Moonlite. I especially like the moonlite of you have one of their focused. But the astrocrumb is why I have now and it works great, even screws onto the nosepiece of my Feathertouch. Less expensive than Lumicon, although theirs looks like it would be really nice.

How are those different to the generic ones from China?

http://pages.ebay.co...lobalID=EBAY-US


 

#12 kfiscus

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Posted 21 September 2015 - 08:51 PM

When I first tried filters, I did the find target-remove EP- thread on filter- reinstall EP method.  All of this risked dropping, fingerprints, cross threading, or being too lazy to use the filter at all.  They're too useful and expensive to just sit in your case.

 

Trying to compare one filter to another using the above method is madness.  It takes too long for the memory of what you saw to remain fresh in the brain.  I then bit the bullet and bought 2" versions of the same filters.  The Astrocrumb filter slide (and most others, I believe) require 2" filters.  I didn't lose my shirt on the upsizing because I had bought used 1.25" filters and bought used 2" filters.  Selling the 1.25" filters was very quick.


Edited by kfiscus, 21 September 2015 - 08:53 PM.

 

#13 mrlovt

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Posted 21 September 2015 - 09:47 PM

Filter preferences are just as personal as eyepiece preferences.  For example, I don't prefer color filters when observing solar system targets, but a lot of people would rather use a color filter if the contrast helps bring out a particular detail.  Here's a nice chart detailing different color filters for different solar system targets:  http://agenaastro.co...ary-filter.html  

 

My favorite general purpose "moon" filter: http://www.telescope...c/63/p/5560.uts  It's variable, so you can adjust just how much light comes through.  It also renders colors naturally, so you don't have to look at green moons.  

 

For DSOs, there are just as many choices.  It boils down to the specific light transmitted by the DSO, so once again, there is no "one size fits all".  Here is a thorough post covering several filters on a number of DSOs:  http://www.cloudynig...isons-r1471#top

 

Here's a good article explaining filters for DSOs:  http://www.prairieas...ep-sky-objects/

 

I hope you find this helpful!  Best wishes and clear skies!  


 

#14 Shorty Barlow

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Posted 21 September 2015 - 09:53 PM

I found this PDF:  http://sas-sky.org/w...al-Filters1.pdf


 

#15 aeajr

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Posted 21 September 2015 - 10:24 PM

Thanks everyone.  I really appreciate the responses.  It is going to take me a while to get all the reference material and, I haven't even tried the ones I have.


 

#16 photonhunter

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Posted 21 September 2015 - 10:33 PM

I noticed that some of the Astronomik filters stated what I assume is the bandwidth of the passbands - e.g. 12nm or 6nm.  some were marked for CCD, but the 6nm ones were not.

 

What bandwidth is better for visual use?


 

#17 penguinx64

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Posted 22 September 2015 - 12:18 AM

I only use colored planetary filters on Jupiter and Saturn.  After trying a bunch of colored filters, I find a #8 light yellow filter useful for both Jupiter and Saturn.  It gives me some improvement without adding too much false color.  It may not be the 'best' colored filter for these planets, but it works ok for me.  The #8 light yellow filter also helps looking at the moon in the daytime and for removing purple fringe.  I can barely see the other planets in my small scopes at less than 180x.  Mars looks like a tiny orange featureless BB and too small to see any detail in my small scopes, regardless of using a filter or not.


 

#18 Starman1

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Posted 22 September 2015 - 01:22 AM

I noticed that some of the Astronomik filters stated what I assume is the bandwidth of the passbands - e.g. 12nm or 6nm.  some were marked for CCD, but the 6nm ones were not.

 

What bandwidth is better for visual use?

Depends.

having 4nm "safety" room on either side of the selected wavelengths is safe.  The more off-axis the light is, the more the bandwidth shifts spectrally.

Ergo, the filter has to be a little wider than the wavelengths.

To wit:

Hydrogen Beta at 486nm: acceptable bandwidth 482-490, or 8nm.  This is a visual-only filter.  Photographers would shoot at the 686nm of H-alpha.

Oxygen III filter (for 496nm and 501nm): acceptable bandwidth 492-505nm, or 13nm

[a photographic O-III is just for the 501nm line, so a bandwidth of 8nm or narrower is fine.]

Narrowband filter for 486nm, 496nm and 501nm: acceptable bandwidth 482-505nm or 23nm. This is a visual-only filter.

As it turns out, those bandwidths are close to what Lumicon offers on their filters.

 

What happens if a filter is narrower?  You run the risk of "clipping" one of the essential wavelengths at a lower transmission level.

What happens if a filter is wider?  More light gets through and the contrast with the sky is reduced.  But, more starlight gets through as well.


 

#19 penguinx64

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Posted 22 September 2015 - 04:22 AM

Sometimes I screw the filters on ahead of time, before going outside. It's much easier in the house with the lights on. But then, I have to know which eyepieces to setup beforehand.


 

#20 aeajr

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Posted 22 September 2015 - 06:48 AM

i am not using any of the filters now but if I find the "light pollution" filter useful I can leave it on one of my eyepieces.   I have 26, 25, 10 and 9.7 eyepieces so one of these could become a dedicated filter eyepiece to make it easy for me to switch and compare.


 

#21 aeajr

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Posted 22 September 2015 - 07:01 AM

 

I'm curious to see your review of the GoSky filter. I considered one of those too. If the 25% ND moon filter isn't dark enough, you could try stacking the GoSky with it. The GoSky filter could improve the view of Jupiter too. But filters are one more thing to fumble with in the dark.


That's why you invest in a filter slide/wheel, one of my better and least expensive upgrades. No more fumbling, just click it in and out of place. Very useful for finding those tiny planetary nebulae.

 

I have seen these but was not sure how well the worked.   Normally you attach the filter to the eyepiece but I guess it doesn't matter if it is not attached.  How many filters in your wheel?   Do you leave it in the telescope all the time?  Which filters are the ones you use most?


 

#22 Shorty Barlow

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Posted 22 September 2015 - 07:57 AM

The only filters I have are from Celestron kits I bought. I have seven Kodak Wratten colour filters consisting of an #80A Blue, #58A Green, #56 Light Green, #25 Red, #21 Orange, #12 Yellow and a #0.9 Moon Filter from the Eyepiece and Filter Kit and three filters from the AstroMaster Kit.

 

gallery_249298_5348_17146.jpg

 

I have found that the #21 Orange and to a lesser extent the #12 Yellow filters are quite good for viewing the Moon in early morning daylight.

 

 

As Mars will be at its closest in late spring early summer next year I’m seriously considering a TeleVue Bandmate Mars A Filter, especially as I’m getting a 9.25“ SCT later this year. I think it’s a distinct possibility the TV Mars A and B filters have been discontinued though.

 

http://www.telescope...ter_1_25__.html

 

http://www.teleskop-...-1-25-Zoll.html


Edited by Shorty Barlow, 23 September 2015 - 08:11 PM.

 

#23 aeajr

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Posted 22 September 2015 - 08:43 AM

 

 

While all the reference material links provided by everyone were great, this one is probably more at my level right now. Thanks Shorty.

 

I had no idea there were so many different types of filters with such specialized uses.   Now I understand why a filter wheel or strip would be so valuable.    Will have to put one on my Christmas list along with some filters.

 

If you insert a filter wheel or strip in the eyepiece I presume it impacts the focusing a bit as the eyepiece is now at a slightly different position.  I presume it does not change magnification. 

 

I presume you would put a filter wheel or strip into the eyepiece hole then the barlow then the eyepiece.  Or would the barlow go in first?  Or does it matter?    Is it better to filter, then magnify or better to magnify and then filter, if that question makes sense.


 

#24 howard929

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Posted 22 September 2015 - 08:54 AM

you already have filters. why ask what anyone else is doing when you can learn the best way possible by finding out for yourself?


 

#25 Jon Tabor

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Posted 22 September 2015 - 09:02 AM

you already have filters. why ask what anyone else is doing when you can learn the best way possible by finding out for yourself?

 

His primary questions are about when to use the filters, and finding resources about what each filter is good at.  If he doesn't ask those with more knowledge, he's looking at spending the next couple of years trying his existing filters in all conditions and keeping track of what they're good at.

 

I think he's asking what everyone else is doing so he can figure out the quickest route to enjoyable observing.  And, frankly, I'm glad he did, because I'm learning a ton.


 


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