Astrophotography Overview
Entering the world of astrophotography is a journey into the unseen. Your specific setup—a **SkyWatcher 200 PDS Newtonian** paired with a **Celestron CG5 German Equatorial Mount**—is a classic, high-performance combination. The 200 PDS is specifically optimized for imaging, featuring a dual-speed focuser and a large aperture to gather photons from faint galaxies.
The camera, your **ZWO ASI 120MC**, serves as a versatile planetary imager or a sensitive guide camera. When used in "Prime Focus" (inserted directly into the focuser without a lens), the telescope becomes the lens. The **CG5 Mount**, equipped with the NexStar+ hand controller, tracks the sky to counteract Earth's rotation.
Advanced Techniques
Once your hardware is communicating, the magic happens in the data acquisition and processing workflow. The goal is to maximize the Signal-to-Noise Ratio (SNR).
Focusing & Stacking
With the SkyWatcher 200 PDS, use the 10:1 reduction knob for fine focusing. A **Bahtinov Mask** is highly recommended. Place it over the tube; it creates a diffraction spike pattern on bright stars. Adjust focus until the central spike sits perfectly between the outer "X" spikes.
**Stacking** is the process of combining images to reduce noise. You will capture:
Light Frames: The actual photos of the stars.
Flat Frames: Crucial for the 200 PDS to remove vignetting (dark corners). Cover the scope with a white t-shirt and shine a light, or use an iPad screen, and take fast exposures.
Dark Frames: Same exposure/temp as lights, but with the lens cap ON to remove thermal noise.
Bias/Offset Frames: Extremely fast exposures (1/4000s) with the cap on to remove electronic read noise.
Software like DeepSkyStacker aligns these images based on star patterns and averages them. This stacking process mathematically rejects random noise while reinforcing the constant signal of the nebula or galaxy.
CG5 & SkyWatcher Setup Guide
Follow these steps to physically connect your specific hardware and configure the software control loop.
1. Tripod & Mount: Set up the CG5 tripod with the "N" leg facing North. Attach the mount head and secure it.
2. Counterweights: The SW 200 PDS is heavy. You will likely need 2x 5kg counterweights. Slide them to the bottom of the shaft *before* adding the telescope to prevent tipping.
3. OTA Attachment: Slide the SkyWatcher dovetail into the CG5 clamp and tighten securely.
4. Balancing: This is critical for the CG5 gears. Unlock the RA clutch and balance the counterweights. Unlock the DEC clutch and balance the telescope tube forward/backward.
We will use a USB Hub to minimize cables running to the laptop.
- USB Hub -> Laptop: Single high-quality USB cable.
- NexStar+ Hand Controller -> USB Hub: Connect the RJ12 jack to the bottom of the Hand Controller. The other end (USB or Serial+Adapter) goes to the Hub.
Note: If using an older Serial cable, you need a Serial-to-USB adapter between the cable and the hub. - ZWO ASI 120MC -> USB Hub: Connect via the standard USB cable.
[Laptop] <=====> [USB Hub]
|-----> [ZWO ASI 120MC] (USB Port)
|-----> [Serial Adapter] -----> [NexStar+ Controller] (RJ12 Port)
Before opening any software, install these in order:
1. ASCOM Platform: The core foundation.
2. Celestron Unified Driver: This allows ASCOM to "talk" to your CG5 mount.
3. ZWO ASI Drivers: Install the native drivers for the 120MC so Windows recognizes it.
4. Celestron NexRemote (Optional): Provides a virtual hand controller on your screen.
Achieving precise polar alignment is mandatory for long exposures. The QHY PoleMaster simplifies this using a camera to track Polaris.
1. Rough Align: Aim your mount North (check with a compass) and set your latitude. Connect the PoleMaster camera via USB.
2. Star Matching: Open the PoleMaster software. Double-click Polaris on the screen and rotate the overlay template to match the surrounding star field.
3. Find Rotation Center: Follow the on-screen prompts. Select a star, then rotate the mount using the Hand Controller (do not move it manually!) so the software can calculate where your mount's RA axis is physically pointing.
4. Monitor Mode: The software will eventually show a green circle (Target) and a red circle (Current Pole).
5. Adjust Bolts: Tweak the mechanical Azimuth (left/right) and Altitude (up/down) bolts on the CG5 base until the circles overlap perfectly.
Read detailed "Use PoleMaster" Guide here
1. Connect Camera: Open APT. Hold "Shift" and click "Connect" on the Camera tab. Select "ZWO Camera" (or ASCOM Camera if preferred). The ASI 120MC should be detected.
2. Connect Mount: In the "Gear" tab, click "Connect Scope". In the ASCOM Selector that pops up, choose "Celestron Telescope Driver".
3. Configure Port: Click "Properties" in the ASCOM selector. Ensure the COM port matches the one assigned to your Serial-to-USB adapter (check Windows Device Manager if unsure).
4. Verify: Once connected, you can slew the telescope using the APT direction buttons.