Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Filer recommendations

equipment eyepieces
  • Please log in to reply
5 replies to this topic

#1 MNLegoBoy

MNLegoBoy

    Lift Off

  • -----
  • topic starter
  • Posts: 19
  • Joined: 28 Dec 2018
  • Loc: MN

Posted 25 February 2020 - 10:37 PM

I know most filters are pretty much useless, but ones like ND, and other light pollution filters I've heard can be useful. I found a 4 pack of different ND filters, at 4, 8, 16, and 1000, but I'm not really sure if I need all the different blocking abilities. Do I just get an ND16 for moon observing, and other bright objects, or something else.


Edited by MNLegoBoy, 25 February 2020 - 10:38 PM.


#2 stoest

stoest

    Ranger 4

  • -----
  • Posts: 325
  • Joined: 04 Jan 2016

Posted 25 February 2020 - 11:15 PM

Filters are an important part of my kit and allow me to see much detail that would otherwise be impossible to see.  UHC, Oiii and H-Beta filters all serve their purpose and do an amazing job when used correctly.  I have a neutral density filter and I've never really found a decent use for it, even on the moon, maybe it's just the one I have but it seems to degrade the image.  As city lights have evolved into more and more different types light pollution filters have become less and less effective and in most situations don't really help much.  Some people do like the ND filters for brighter objects and some get use out of LP filters so your mileage may very.

 

If you want to learn about how filters work on different objects, this is a great place to start: https://www.prairiea...common-nebulae/


  • lsfinn and havasman like this

#3 ascii

ascii

    Vanguard

  • -----
  • Posts: 2,244
  • Joined: 04 Jun 2016
  • Loc: Orlando, FL, USA Approximately 28.5ºN,81.5ºW

Posted 26 February 2020 - 07:23 AM

The only things I've found ND filters useful on are the Moon and Venus.  Some say to just use more magnification to tame the excessive brightness. That works, but sometimes I want a wider view of the Moon that ends up too uncomfortable without my ND13 filter.  Venus in particular can end up being a blob of blinding light that only takes shape when I put on my ND13 filter.  I wouldn't think you'd need a set.  Either an ND13 or ND25 should be adequate.  I haven't seen an ND16, but if it's of good quality, it should do.

 

I have had success with narrowband (often called UHC) filters for emission nebulae.  The improvement under my heavy light pollution is modest, but it can mean the difference between seeing and not seeing M8 or M20.  Just be sure to get a good one like the newer Lumicon UHC, Tele Vue Bandmate-II Nebustar UHC, Astronomik UHC, or DGM Optics NPB.


Edited by ascii, 26 February 2020 - 12:32 PM.

  • kevint1, lsfinn and brentknight like this

#4 epee

epee

    Soyuz

  • *****
  • Posts: 3,569
  • Joined: 30 Nov 2006
  • Loc: Suh-van-nuh, Jaw-juh

Posted 26 February 2020 - 10:11 AM

I will sometimes use ND filters on the Planets. I find the glare reduction helps me see subtle detail more easily. I will even go so far as to stack a mild ND with some other planetary filter, Wratten or Multiband; this is when using my 12" scope.


  • lsfinn likes this

#5 macdonjh

macdonjh

    Fly Me to the Moon

  • *****
  • Posts: 5,158
  • Joined: 06 Mar 2006

Posted 26 February 2020 - 12:09 PM

I know most filters are pretty much useless

I don't know why you'd say that.  With 8" of aperture, your XT8 will gather enough light to make filters helpful.  Just make sure you use 100x or so magnification (rather than 200x+) to keep your exit pupil big enough.  I find a UHC filter quite useful for many nebulae.  I typically use higher magnification, or sacrifice my dark adaptation when viewing the moon. 

 

I was surprised to find Orion's Mars filter effective as well.  I plan to use it again this summer and fall.

 

Enough experienced observers have commented about O-III filters to make me almost ready to start saving for one.

 

A -V filter really helped me split Antares with my achromatic refractor.  It also had the extra benefit of turning Antares B really green.

 

For the planets, I prefer natural colors, so I don't often use color filters.  My son; however, used to love turning the moon green or blue.



#6 lsfinn

lsfinn

    Mariner 2

  • *****
  • Posts: 251
  • Joined: 28 Jan 2013
  • Loc: Santa Fe, NM

Posted 26 February 2020 - 02:32 PM

I know most filters are pretty much useless, but ones like ND, and other light pollution filters I've heard can be useful. I found a 4 pack of different ND filters, at 4, 8, 16, and 1000, but I'm not really sure if I need all the different blocking abilities. Do I just get an ND16 for moon observing, and other bright objects, or something else.

The point of ND filters is to reduce image brightness; so, you'll only use them when the image is so bright as to be uncomfortable. For an 8" scope you might find an ND 1.8 (same meaning as ND64) useful for Moon and Venus. You shouldn't need anything more. 

 

If you want some flexibility you might consider getting to ND 1.8 by stacking two ND 0.9: one ND 0.9 would be useful for a crescent moon, while the stacked pair for would be more useful for first quarter to full Moon. 

 

For comparison I have a 22" scope and I stack and ND 0.9 and an ND 1.8 - same as stacking an ND8 and an ND64 - for lunar viewing. I find this plenty bright, but comfortable. The effect of ND 2.7 is to reduce the brightness by a factor 512. Your 8" scope has about 1/8 the light collecting area; so, for the equivalent brightness you need reduce your image brightness by a factor of 1/64, which is ND1.8 (or ND64). 

 

Other filters - either color filters for planetary viewing, narrow-band light pollution filters, or other narrow-band filters (UHC or equivalent, OIII, H-beta) - are used to increase the contrast between the night sky and the object you are looking at. For example, much of the light from planetary nebulae comes from two emission lines associated with OIII ionization. A filter that passes just OIII will not dim these much; however, it will dim any continuum emission (such as other stars and incandescent light pollution), or light pollution from, e.g., sodium vapor street lamps. 

 

The same is true for colored filters applied to planets. If there are features on a planet (e.g., Jupiter's Great Red Spot) that you want to enhance, you might choose a filter that is complementary (in this example, blue): this will increase the contrast of the feature against the planet background. 

 

Like @stoest and @ascii I've found that narrowband filters - a UHC (Lumicon) or NPB (DGB) - make a huge difference in the ability to see bright nebulae, and an OIII makes a huge difference in the ability to identify and/or resolve planetary nebulae. In my previous location the Veil was simply impossible until I saw it through a UHC filter.


Edited by lsfinn, 26 February 2020 - 02:52 PM.



CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics





Also tagged with one or more of these keywords: equipment, eyepieces



Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics