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Having a tough time trying to decide which type of filter you need ? Read on to see if we can help shed some light for you !! 



Which Nebular filter for DSOs and Astrophotography

Date: 09/05/2010

We have several kinds of filters in stock.

Firstly, they typically come in 3 sizes : 1.25", 2", and SCT. The first 2 sizes fit 1.25" and 2" eyepieces or barlows, and the SCT format fits the rear cell of SCT telescopes. Here's a matrix to help you decide which size to get :

  1.25" 2" SCT
Telescope has SCT Rear cell
Telescope takes 2" eyepieces
Telescope takes only 1.25"
Prime Focus photography Adapter needed Adapter needed Simple
Eyepiece projection Simple Simple Simple
Typical price range $100-S$200 $120-S$400 S$130-S$400

There are also basically 4 types of Nebular filters. They are Light Pollution Reduction (LPRs) (also known as  Broadband), Narrowband (also known as Ultra High Contrast - UHC), Oxygen III, and Hydrogen-beta. These types are all named based on which frequencies of light they let through.

  LPR Narrowband OIII H-
Filters out stray photons from street lamps, and dim skyglow
Light pollution level mild moderate extreme minimal
Transmission >90% >90%    
Filter passes 450-530, >650nm 480-505nm* 496-501nm* 486.1nm*
Contrast low moderate highest possible specific
Stars and Star clusters, spiral galaxies (M33, M101)
photos only
Diffuse Nebula : Crab (M1), Lagoon (M8), Great Orion (M42) Swan  
Reflection Nebula : Pleiades, Trifid      
DSO spread over wide area : Veil, Rosette, N. American. Emission nebula : Lagoon, Omega.  
Planetary nebula : Dumbell, Ring  
Faint planetary nebulas : NGC7293, Bell 33, Jones 1      
Horsehead, California, Cocoon nebula      
For visual use
For astrophotography *

Wavelengths of interest :
560nm = yellowish light of sodium and mercury vapor street lights and airglow.
500nm = ionized oxygen and atomic hydrogen
486.1nm = atomic hydrogen-beta, blue-green
656.3nm = hydrogen alpha, red color

* Reduces sky fogging, exposure possible to increase by 3x

Lastly, it can be confusing to figure out how to compare filters sold by the various manufacturers so here are the names used by them :

  LPR Narrowband OIII H-
Orion SkyGlow
OIII H-beta
Lumicon Deep Sky UHC OIII H-beta
Astronomik CLS UHC, UHC-E OIII H-beta
Thousand Oaks Broadband Narrowband OIII H-beta
Meade Broadband Narrowband OIII  
Hutech LPS      
Televue   Nebustar OIII  

Hope this helps !!

Joo Beng


Which colour filter do I need?

Date: 09/05/2010

Here's a table summarising the different objects that can benefit from different colour filters:

  Blue Red/Orange Green Yellow Violet
lunar features

lunar features

lunar features

lunar features
for daylight and twilight observations
faint features and details
dark dusky areas of upper clouds

for daylight obs, terminator views

for daylight obs, cloud patterns
darker areas and upper clouds
surface features, clouds, polar caps

sharpens boundaries of yellow dust clouds, ice caps. surface features

contrast for polar caps, dust storms, clouds

surface features, dust clouds

detects haze or clouds over polar caps
contrast in cloud belts, Great Red Spot
Great Red Spot, blue-red low contrast in belts

orange-red features of belts, polar regions
low-contrast details, belts, zones

bluer clouds, polar regions

contrast in white objects in atmosphere

orange-red features of belts, zones

enhances ring structure
Enhances tails. Combine with orange for sodium D line.

Enhances dust tails
highlights yellow dust tails and heads

Hope this helps !!

Joo Beng


Common Light Pollution Emissions:

Mercury Street Lights: 410, 435, 540, 580, 605, 615nm
Sodium Street Lights: 570nm
Ionized Oxygen Skyglow: 555, 620nm



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