Narrowband CCD Imaging Don Goldman, Ph.D. Astrodon Imaging May, 2011
www.astrodonimaging.com
Equipment Sierra-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,Apogee U16M/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
NGC253
Galaxies 47Tuc
Star Clusters Emit light over a continuum of wavelengths
NGC1579
Reflection Nebula
Narrowband Objects
NGC7822 Helix
Emission Nebula
Planetary Nebula, Wolf-Rayet Bubbles
Emit light at discrete wavelengths due to ionization from nearby UV sources
Vela
Supernova Remnants
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 Hubblelike images • Hybrid color NB + RGB stars
NGC3576
Natural Color + Great Detail with 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?
Bandwidth 120 nm 80 nm 5 nm
Photometric Red Imaging Red OIII
Photometric Red Imaging Red (UVBRI) (RGB)
H-alpha
H-alpha
SII
H-alpha
Contrast Improvement Crescent Nebula, Wolf-Rayet Bubble in Cygnus, NGC 6888
Wide Red (Orange)
Narrow Red
H-α 9 nm
H-α 6 nm
3x5min exposures, RCOS 12.5” Ritchey-Crétien, SBIG STL11000XM CCD, Bisque Paramount ME
H-α 4 nm
Enhanced Structure at Hi-Res Crescent Nebula in Cygnus, NGC 6888
Conventional RRGB (courtesy Rob Gendler)
Red = H-Îą Blue=Green=OIII (Don Goldman)
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
Narrowband Filter Photometric Red Imaging Red OIII
H-alpha
SII
For highest S/N (contrast):
H-a Filter Transmission Plot 100
% Transmittance (I/Io)
90 80 70
6 nm
40 30 20
FWHM, or bandwidth (controls noise, N, or non-emission signal
Peak Transmittance (controls Signal, S)
60 50 100 photons
1. Highest transmittance 2. Smallest bandwidth
93 photons
Background ADU count scales with FWHM
10 0 640
645
650
655 Wavelength, nm
660
665
670
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 upshifted filter • See our research http://www.astrodon.com/Orph an/astrodonfaqnarrowband/
Image courtesy of Cesar Quiroga, QSI540 Epsilon180, 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 Photometric Red Imaging Red OIII
H-alpha
SII
• 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?
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
H-a 3 nm
OIII 3 nm
SII 3 nm
Photoshop Processing Mapped Color 1. Add H-a, OIII. SII preprocessed, registered 16-bit TIF files and label 2. Convert image to RGB 3. Create hue/saturation (H/S) adjustment layer for each layer a) Click colorize in H/S adjustment layer b) Slide saturation to 100% c) Slide Lightness to -50 d) 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 taste 6. Add curves adjustment adjustment layers as needed
Clipping Layer Mask SII
Repeat for OIII Turn 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 donâ&#x20AC;&#x2122;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
PuWe1
MWP1
NGC246
YM16
Abell 31
NGC6164
â&#x20AC;˘ Two OIII layers (G,B), H-a (red/magenta)
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 layer 2. Select Filter/Other/High Pass 3. 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 light 6. Adjust opacity to taste 7. Select hide-all layer mask from Layers 8. Use brush in foreground (white) mode 9. Adjust brush size 10. Paint over just the areas you want sharpened avoiding stars 11. Collapse and save as single-layer 16-bit TIF for prints 12. 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