GALAXIES - COURSE 1

C1: Galaxy Season: Capture & SIRIL PP (Post Processing) Tips & Tricks for your Captures!

Alright, Astro-nuts, Galaxy Season is in full swing, and the DwarfVision Challenge is heating up! Springtime skies offer that incredible window out of our Milky Way, revealing a universe teeming with distant galaxies. Your DWARF II or D3 is a fantastic little galaxy-hunting machine, but these faint fuzzies can be tricky. So, let's dive into some tips and tricks to help you capture and process the best possible images for the challenge!

Part 1: At the Scope – Maximizing Your Galaxy Data

TIP1: Capture Settings

1. Dark Skies are Your Best Friend (Especially for Galaxies!): Galaxies are faint. While the DWARF scopes do a great job with light pollution, nothing beats truly dark skies for picking up those subtle outer arms, faint companions, or elusive Integrated Flux Nebula (IFN). Leverage your DWARF's incredible portability – pack it up and head to the darkest site you can reasonably access. Every bit of sky darkness helps!

Plan ample exposure time if the backyard is tonight's best option (you cannot always run off to the hills!). Aim to dedicate the same three-hour window over two or three nights, pushing your capture to 800 to 900 subs, you can then create a "Mega-Stack" in the DWARFLAB App, SIRIL, PixInsight, or your favourite star stacker to significantly boost your signal-to-noise ratio.

With 9+ hours of exposures over multiple nights on M81 & M82, even faint details like the Integrated Flux Nebula (IFN) can be captured. These delicate structures can be revealed through careful stretching in your preferred image processing software, as shown in this example, enhanced in Lightroom.

Don't settle for anything less than 1 degree of deviation; keep hitting that "be more precise" button till you have it perfect.

TIP2: Nail That Polar Alignment (EQ Mode is Key)!

Precise polar alignment in Equatorial (EQ) mode is non-negotiable for long imaging sessions on faint galaxies.

Why it Matters: Good polar alignment means your DWARF will track the stars accurately for longer, leading to sharper stars and allowing for longer total integration without field rotation issues. This is crucial for stacking many sub-exposures.
The Indentations: Remember, before starting the app's polar alignment routine, physically align those small indentations—one on the DWARF scope body and the corresponding one on the rotating base of the L-bracket. This sets the crucial "home" position. NOTE: I have found the best results with fewer tracking issues when these indentations point to the ground (in the Northern Hemisphere) than when pointing to the sky.
App Assist: Then, diligently follow the DWARFLAB app's polar alignment procedure. If you're two degrees off, adjust again until you're at zero degrees. Take your time with the adjustments; they're worth it!

TIP3: Exposure Time & Gain – Finding the Sweet Spot:

Exposure Length: For most galaxies with the DWARF scopes, individual exposures between 15 and 30 seconds in EQ mode on the D3 usually work well. This balances signal collection with keeping stars from bloating too much, and from the scope losing a lot of data. 45-60 second exposures can result in a lot of lost frames.
Gain: A moderate gain setting is often best. Too low, and you might not pick up faint details; too high, and noise becomes more problematic. Experiment, but a mid-range setting (e.g., 60-80 on the D3, or equivalent on the D2) is a good starting point.
Astro Filter: The built-in Astro Filter is essential for broadband targets like galaxies. It allows for natural star colours and reduces star bloat from infrared light during long exposures. Some galaxies with bright cores or emission nebulosity in their spiral arms, such as M31 and M33, may warrant a session with the Dual-Band filter.
Total Integration Time: More is MORE! This is the single most significant factor for good galaxy images. Galaxies are dim!

Stack, Stack, Stack: Aim for hours of total exposure time, not minutes. For faint details or IFN, 5, 10, or even 20+ hours collected over multiple nights is common for stunning results.
Multi-Night Sessions: The DWARF makes multi-night projects easy. Save your sessions and keep adding data when the skies clear.

Unveiling M101: The power of stacking more exposures at 60 gain. Notice how details in the spiral arms emerge as the sub count increases from 50 to 250.

Atlas view of M13: Once an object has been selected, press the camera icon in the lower right to initiate the scope's GOTO.

Additional Framing & Target Acquisition Tips:

Once you have set up for the evening and completed the EQ Setup, calibrate the scope. You can turn off the auto-calibration setting as long as you don't change anything for the rest of the night.
Open the Atlas and find your target. It’s easiest if you know what target you're going for before you shoot. For this purpose, I love Setellarium online: https://stellarium-web.org/. Type in the M (Messier) or NGC designator of your target and touch the camera icon at the lower right.
Once the GoTo has found your target, take a short test exposure to confirm framing, allowing the scope’s tracking to settle in. Ensure your target galaxy and any companions or interesting background galaxies are well-placed.
Optimal settings: Open the Astro mode settings menu to the right, and ensure your scope is set up at 4K with .fits as the output (as long as you're not using a .tiff stacker). Then, turn off the AI processing setting if you plan to stack the resulting stack yourself.

Part 2: Post-Processing – Multi-session stacking with SIRIL

TIP1.1: Stacking Setup

You've got your data (hopefully lots of .fit files!)., and now it's time to process it. SIRIL is a great free tool that works wonders with DWARF data. Photoshop, GIMP, or Lightroom often follow it up for final post-processing touches. (I will present this in COURSE 2)

NOTE: Siril has a steep learning curve. if you're having issues stacking your first captures, use the resources I have collected at right

1. Stacking in SIRIL (or your preferred software) – Using the OSC Preprocessing Script:

A popular and efficient way to stack your DWARF data in SIRIL is by using its built-in scripts, particularly the OSC_Preprocessing.ssf script (for One-Shot Color cameras like the DWARF's). Here’s a typical workflow:

Calibration Frames:
- If your DWARF scope generated automatic calibration frames (darks, biases), you'll find them in the CALI_FRAME folder on the DWARF's SD card for that imaging session. These are typically master frames (e.g., dark_stacked.fit, bias_stacked.fit).
- The DWARF usually provides one master bias per session if auto-calibration is on. Flats are less common with the DWARF and might not be present.
Organize Your Files:
- On your computer, SIRIL's scripts expect a specific folder structure within its working directory (by default, this is usually your computer's "Pictures" folder, or a "Siril" subfolder within it). Create these exact folder names if they don't exist:
  - biases
  - darks
  - flats (can be empty if you don't have flats)
  - lights
- Copy your master bias file (e.g., bias_stacked.fit) from the DWARF's CALI_FRAME folder into your new biases folder.
- Copy your master dark file (e.g., dark_stacked.fit) from the DWARF's CALI_FRAME folder into your darks folder.
- Copy all your light frames (your actual images of the galaxy, e.g., stacked_15s_gain60_... .fit) from the DWARF's session folder(s) into the lights folder. Crucially, ensure you remove or rename any files with "Failed" in their name, as these will cause the SIRIL script to fail.

Tip1.2: Stacking in SIRIL

Running the Script in SIRIL:
- Open SIRIL.
- Ensure SIRIL's "home" directory (working directory) is set to where you created the biases, darks, flats, and lights folders (usually Pictures by default – you can change this in SIRIL's preferences if needed).
- Go to the "Scripts" menu.
- Select OSC_Preprocessing.ssf (or OSC_Preprocessing_WithoutFlat if you have no flats and want to be explicit, though the main script handles missing flats).
- Click "Run."
The Result: If all files are correctly placed and named, and there are no "Failed" light frames, the script will automate the calibration, registration, and stacking process. It will output a final stacked image, typically named Result.fits (or similar, depending on the script version), in your working directory. This Result.fits file is then ready for further processing like color calibration and stretching.
Manual Stacking: Alternatively, you can always perform these steps (calibration, registration, stacking) manually using SIRIL's GUI if you prefer more control or if the script encounters issues.

View at SIRIL

Seestar Specific

Download SIRIL

A new - current version specific - Siril walkthrough on YouTube

To See the Result.fit in SIRIL: Turn on AutoStretch!

Viewing Your Data in SIRIL: When you open a stacked image (like result_12390s.fit here), it will likely appear black. The crucial first step is to select 'AutoStretch' from the display mode dropdown (bottom right) to reveal your deep-sky object visually.

M101 - The Pinwheel Galaxy emerging! This is the Result.fits from stacking 368 light frames using SIRIL's OSC Preprocessing script. Ready for color calibration and stretching to bring out its full glory!

TIP2: Plate Solving – The Essential First Step for Colour!

Why? As we've discussed, before you can perform Photometric Colour Calibration, SIRIL must know precisely where your image is pointed in the sky. Plate solving achieves this by identifying star patterns in your image and matching them to astronomical catalogues, giving your image an exact celestial address.
How: With your stacked image open (like an M101 capture, for instance, which would be at this stage), navigate to SIRIL's plate-solving tool. This is typically found under the "Image Processing" menu -> "Astrometry" -> "Plate Solving."
- Enter Key Parameters: It's crucial to accurately input your telescope's Focal Length (100mm for both DWARF II and D3 telephoto lenses) and Pixel Size (1.45µm for both DWARF II and D3 telephoto sensors).
- Get Coordinates: In the "Object name" field within the Plate Solving window, type the name of your primary target (e.g., "M101") and click the "Find" button. SIRIL will query online databases to pre-fill the Right Ascension (RA) and Declination (Dec) coordinates, which significantly helps the solving process.
- Solve! Click "OK" to run the plate solving. Keep an eye on the console output at the bottom of SIRIL. A "Plate solving successful!" message means you're good to go! If it fails, double-check your focal length and pixel size parameters, ensure your image has a decent number of clear, round stars, and that the object name search returned sensible coordinates.

Plate Solving Success! Here's M101 after a successful plate solve in SIRIL. Notice how the software has identified the main galaxy and numerous surrounding NGC objects (HII regions and companion galaxies like NGC 5477). This celestial 'address' is now locked in, ready for accurate Photometric Colour Calibration.

To see the above green designators, hit the "OBJECTS NAMES" icon in SIRIL's lower interface.

After running the PCC, the galaxy colour is still on the "green side." The step "Remove Green Noise" is a must before the next step.

TIP3: Photometric Colour Calibration – (SIRIL 1.4.0-beta1+)

Photometric Colour Calibration – For True Galaxy Colours (SIRIL 1.4.0-beta1+): Once your image is plate-solved (like the M101 example), you're set for Photometric Colour Calibration. In SIRIL (e.g., version 1.4.0-beta1), find this tool under Image Processing -> Colour Calibration.

Ensure your target's name (e.g., "M101") is at the top of the pop-up (in older versions) window, so SIRIL uses the solved coordinates.
Under "Catalogue Parameters," "APASS" or "Gaia" are good choices for the Photometric Star Catalogue. Leave "Catalogue Limit Mag" on "Auto" or start around 12-14 if manual.
In the "Background Reference" section, ensure "Automatic detection" is checked.
The tool inherently uses stellar photometry for white balance. Click "OK." SIRIL will then fetch star data and balance your image colours for a natural look.
Tackling Green Casts: Photometric Color Calibration with background neutralization should eliminate most green (or other color) casts. If a stubborn green tint remains, use SIRIL's Image Processing -> Color Calibration -> Remove Green Noise tool after PCC but before proceeding to background extraction or significant stretching.

TIP4: Background Extraction

Taming Gradients: After color calibration and addressing any strong color casts, you might still have some light pollution gradients or unevenness in your background. Access this tool via Image Processing -> Background Extraction.

Interpolation Method: "RBF" (Radial Basis Function) is a common and effective choice.
Adjust Parameters: You can fine-tune settings like "Smoothing," "Samples per line," and "Grid tolerance." For "Samples per line," a value around 10-15 often works as a starting point; adjust based on the complexity of your background. "Grid tolerance" helps the algorithm decide how aggressively to place samples.
Generate Samples: Click the "Generate" button. SIRIL will automatically place sample boxes in what it determines to be background areas (avoiding your galaxy and bright stars). Review these samples. You can manually add more samples by left-clicking on background areas or remove incorrectly placed samples by right-clicking on them.
Compute & Apply: Once you're happy with the sample placement, choose your "Correction" method (usually "Subtraction"). Click "Compute Background" to see a preview of the background model SIRIL has created. If it looks good, click "Apply" to subtract this model from your image.
Order: Some prefer to do background extraction before colour calibration, especially if gradients are severe. Experiment to see what works best for your image.

M101 Before (above) background removal and after (below), note how much the contrast of faint details has improved from the PCC step.

If green noise is still apparent, another round of removing the noise can be performed.

SIRIL Workflow: From a dark linear stack (top, 'Linear' view), use Histogram Transformation (bottom) for an initial stretch to reveal your galaxy before further processing.

TIP5: Stretching the Data – Revealing the Faintness:

Your stacked, color-calibrated, and background-extracted image will still look very dark (linear). Before moving to Photoshop for more detailed tonal adjustments, perform an initial stretch in SIRIL to reveal the galaxy.

Visualize First: In SIRIL's main window, ensure your image is visible by selecting "AutoStretch" from the display mode dropdown (bottom right, as shown in the screenshot with the green arrow). This is just a preview. To make the change permanent for export, you'll use the Histogram Transformation.
SIRIL's Histogram Transformation: Access this via Image Processing -> Histogram Transformation.
- Use the Shadows, Midtones, and Highlights sliders to gently bring out the galaxy. A common approach is to move the Midtones slider to the left to brighten the galaxy's structure and the Shadows slider slightly to the right to ensure a dark background.
- The goal here is a balanced, non-clipped image that shows the main features, ready for more nuanced work in Photoshop. Avoid overstretching or losing highlight detail at this stage.
- Click "Apply" when satisfied.

Next up: removing the noise for sharp details, as seen in the SIRIL completed image above, plus how to give your image amazing colour!

Thanks for reading, this is the conclusion of course 1, Course 2 - Detail & Colour is coming soon!

Coming In the next post! – Colour & Details for Photoshop, RC Astro's & Topaz Filters + Lightroom

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