Narrowband CCD Imaging

Don Goldman, Ph.D.Astrodon Imaging

May, 2011

www.astrodonimaging.com

EquipmentSierra-Remote Observatories

• Bisque Paramount ME (MKS400)• RCOS 16” RC tube, Apogee U16M/CFW,

PIR/TCC, Astrodon MonsterMOAG, ST-402 guider

• FSQ106N, MonsterMOAG, SBIG Remote Guide Head, STL11000/FW8, Robofocus

• Bisque Paramount ME (MKS400)• RCOS 14.5” Classical Cassegrain

Truss, PIR/TCC,ApogeeU16M/CFW, Astrodon MonsterMOAG, ST-402

• AP130, Apogee U16M/CFW, RoboFocus

Topics• What is narrowband imaging?

• Benefits• Narrowband filters

• Mapped Color Processing Tutorial

M1

Broadband Objects

Emit light over a continuum of wavelengths

GalaxiesNGC253

Star Clusters

47Tuc

ReflectionNebula

NGC1579

Narrowband Objects

Emit light at discrete wavelengths due to ionization from nearby UV sources

EmissionNebula

NGC7822

Planetary Nebula,

Wolf-Rayet Bubbles

Helix

SupernovaRemnants

Vela

Benefits of NB Imaging

• Enhanced structural contrast• Use in light-polluted locations

• Extend use of equipment when moon is up

• Add H-a to LRGB for more structure

• Mapped NB color for Hubble-like images

• Hybrid color NB + RGB stars

NGC3576

Natural Color + Great Detailwith H-a/OIII in PN

PuWe1 MWP1 NGC246

YM16 Abell 31 NGC6164

NB for Extended Halos – M97

Normal 3 nm OIII Combined

What is Narrowband?

Photometric Red Imaging Red H-alpha(UVBRI) (RGB)

H-alpha

Photometric RedImaging Red

OIII H-alpha SII

Bandwidth120 nm80 nm5 nm

Contrast Improvement

Wide Red (Orange)

Narrow Red H-α 9 nm H-α 6 nm H-α 4 nm

3x5min exposures, RCOS 12.5” Ritchey-Crétien, SBIG STL11000XM CCD, Bisque Paramount ME

Crescent Nebula, Wolf-Rayet Bubble in Cygnus, NGC 6888

Enhanced Structure at Hi-Res

Conventional RRGB(courtesy Rob Gendler)

Red = H-αBlue=Green=OIII(Don Goldman)

Crescent Nebula in Cygnus, NGC 6888

Comparison of 3 vs 6 nm OIII

• 20” RC• Full Moon• Background ADU decreased from

5700 to 1800• Gradient gone• Smaller stars• Greater faint detail• Moonlight strongest at OIII

Photometric RedImaging Red

OIII H-alpha SII

H-a Filter Transmission Plot

0102030405060708090

100

640 645 650 655 660 665 670Wavelength, nm

% T

rans

mitt

ance

(I/Io

)

Narrowband Filter

Background ADU count scales with FWHM

FWHM, or bandwidth(controls noise, N, or non-emission signal

For highest S/N(contrast):

1. Highest transmittance

2. Smallest bandwidth

Peak Transmittance(controls Signal, S)

100 photons

93 photons

6 nm

Narrowband Filter Selection• 4.5 - 7 nm FWHM

• All 5 nm is good starting point• Good for most scopes – f/10 to f/3

• Moonlight• More at blue-green OIII (more gradients)• Less for deep red H-a, SII

• Consider narrower OIII (3 nm) to reduce moonlight • Consider 3 nm if you have severe light pollution• Start with H-a first, then add OIII, then SII• Can mix FWHM

• Astrodon 5 nm H-a/SII and 3 nm OIII (my Australian setup)• All Astrodon 3 nm (my Yosemite remote setup)• Personal note – fine detail is AMAZING with 3 nm

• Your budget

3 nm and Fast Optics• Decrease signal

~10-12% at f/2.9• Starting high at

93%T (10% loss still > 80%T)

• Background < ½ of 7 nm filter

• Do not need special upshiftedfilter

• See our research http://www.astrodon.com/Orphan/astrodonfaqnarrowband/

Image courtesy of Cesar Quiroga, QSI540 Epsilon-180, Astrodon 3 nm H-a

Narrowband Processing Tutorial

Melotte15 in The Heart Nebula, IC 1805

Goals• Demonstrate clipping layer mask method• Achieve rich, vibrant colors• Improve color of NB Stars• Add 3-D “feel” to our 2-D data• Multiscale High-Pass Filtering

Color Mapping

• Combining Blue, Green, Red, is obvious– All you need is the weighting

• Dual NB (H-a, OIII) – Supernova remnants, planetary nebula - natural look– B ~ G = OIII, R = H-a

• Tricolor NB (H-a, OIII, SII)– Both SII and H-a are red– Hubble (HST) palette (B = OIII, G = H-a, R = SII) most common– CFHT palette (B = SII, G = OIII, R = H-a)

• NB Weights?

Photometric RedImaging Red

OIII H-alpha SII

NB Color Combine Methods• Assign RGB in Maxim, CCDStack, Image

Plus….– Once weights are used and combined, cannot go back

• Preprocess and merge channels in Photoshop– www.flemingastrophotography.com (Neil Fleming)– Once weights are used and combined, cannot go back

• Clipping Layer Mask– http://old.astrodon.com/oldsite/RectorImageProcessing.pdf (Dr. Travis Rector,

U. Alaska)– http://www.imagingdeepsky.com/Presentations.html (Ken Crawford)– Most flexible– Can change hue, intensity, saturation at any time in the process

Clipping Layer Masks in Photoshop• Each NB (H-a, SII, OIII) layer is

in Screen (projector) mode• Each NB layer has a hue/

saturation layer mask• Each layer mask is “clipped”

only to the NB layer immediately below

• Change hue (color) and intensity for each NB independently at any time in the process

• Can add other clipping layer masks, e.g. curves for each NB

Colors are superimposed in

Screen mode as if 3 projectors were used

Melotte 15 in IC 1875 - Masters

SII 3 nmOIII 3 nmH-a 3 nm

Photoshop ProcessingMapped Color

1. Add H-a, OIII. SII preprocessed, registered 16-bit TIF files and label2. Convert image to RGB3. Create hue/saturation (H/S) adjustment layer for each layer

a) Click colorize in H/S adjustment layerb) Slide saturation to 100%c) Slide Lightness to -50d) Slide Hue to 120 for H-a (Green)e) Slide Hue to 230-240 for OIII (Blue)f) Slide Hue to 360 for SII (Red) g) Right click adjustment layer and select “create clipping layer

mask”4. Select “Screen” blending mode for H-a, SII and OIII image layers (not

layer masks)5. Adjust lightness to taste6. Add curves adjustment adjustment layers as needed

Clipping Layer Mask SII

Repeat for OIIITurn off SII screen layer first to see OIII layer

Complete with H-a

Turn Other Layers On

Adjust SII Overall Intensity• Double click on H/S SII adjustment layer• Change the Lightness from -51 to -42

Add SII Curves Clipping Layer Mask

Add H-a Curves Clipping Layer Mask

If you don’t like it, just turn the curves layer off. Cannot turn off the Hue/ Saturation layer.

Change to “Natural Color”• Many do not like the HST color palette• SII is red• Change (green) H-a Hue to red/magenta

PN in Natural Color with H-a/OIII

• Two OIII layers (G,B), H-a (red/magenta)

PuWe1 MWP1 NGC246

YM16 Abell 31 NGC6164

Add RGB Stars• NB stars are

unattractive• Often have

magenta halos• Remove

magenta halos with Selective Color and then Desaturate

• Add RGB stars as top layer

• Blending mode to Lighten Color

Photoshop Processing Selective High-Pass Filtering

1. Duplicate layer2. Select Filter/Other/High Pass3. Select a pixel scale of ~7 for sharp detail (e.g. tendrils)4. Select a pixel scale of ~35-45 for large scale (e.g. galaxy arms)5. Change the blending mode to overlay (sharper) or soft light6. Adjust opacity to taste7. Select hide-all layer mask from Layers8. Use brush in foreground (white) mode9. Adjust brush size 10.Paint over just the areas you want sharpened avoiding stars11.Collapse and save as single-layer 16-bit TIF for prints12.Save 8-bit 72 dpi JPEG file for posting

High Pass Filtering in Photoshop

Fine High Pass (5-9 pixels) to bring out fine structure (e.g. filaments)

Coarse High Pass for 3-D

Review• What is narrowband imaging• Narrowband filters• Benefits• Mapped color using clipping layer masks• Luminance layer• High pass filtering for 3-D effect• Magenta star cleanup• Adding RGB stars• Questions?

Contact: don@astrodon.com

Thank You!!Clear Skies