Astrophotography Calculator

Astrophotography Field of View & Image Scale Calculator

Calculation Results:

Horizontal Field of View: — degrees

Vertical Field of View: — degrees

Image Scale: — arcseconds/pixel

function calculateAstroParams() { var focalLength = parseFloat(document.getElementById('focalLength').value); var sensorWidth = parseFloat(document.getElementById('sensorWidth').value); var sensorHeight = parseFloat(document.getElementById('sensorHeight').value); var pixelSize = parseFloat(document.getElementById('pixelSize').value); if (isNaN(focalLength) || focalLength <= 0 || isNaN(sensorWidth) || sensorWidth <= 0 || isNaN(sensorHeight) || sensorHeight <= 0 || isNaN(pixelSize) || pixelSize <= 0) { document.getElementById('horizontalFoV').innerText = 'Invalid Input'; document.getElementById('verticalFoV').innerText = 'Invalid Input'; document.getElementById('imageScale').innerText = 'Invalid Input'; alert('Please enter valid positive numbers for all fields.'); return; } // Calculate Field of View (FoV) in degrees // FoV = 2 * atan(sensor_dimension / (2 * focal_length)) * (180 / PI) var horizontalFoV_rad = 2 * Math.atan(sensorWidth / (2 * focalLength)); var horizontalFoV_deg = horizontalFoV_rad * (180 / Math.PI); var verticalFoV_rad = 2 * Math.atan(sensorHeight / (2 * focalLength)); var verticalFoV_deg = verticalFoV_rad * (180 / Math.PI); // Calculate Image Scale (arcseconds per pixel) // Image Scale = (pixel_size_microns / focal_length_mm) * 206.265 // 206.265 is a constant for converting radians to arcseconds (180/PI * 3600 / 1000 for microns to mm) var imageScale = (pixelSize / focalLength) * 206.264806247; // More precise constant document.getElementById('horizontalFoV').innerText = horizontalFoV_deg.toFixed(2); document.getElementById('verticalFoV').innerText = verticalFoV_deg.toFixed(2); document.getElementById('imageScale').innerText = imageScale.toFixed(2); }

Understanding Your Astrophotography Setup

Astrophotography is a captivating hobby that combines astronomy with photography. To capture stunning images of celestial objects, it's crucial to understand how your equipment interacts with the night sky. This calculator helps you determine two fundamental parameters: your Field of View (FoV) and your Image Scale.

What is Field of View (FoV)?

Your Field of View refers to how much of the sky your camera and telescope combination can capture in a single frame. It's essentially the angular size of the patch of sky that will appear in your photograph. A wider FoV is suitable for large objects like nebulae and galaxies, while a narrower FoV is ideal for smaller, more distant targets or for capturing fine details on planets and the Moon.

The FoV is determined by two main factors:

• Telescope Focal Length: A longer focal length (higher magnification) results in a narrower FoV, showing a smaller area of the sky in greater detail. A shorter focal length provides a wider FoV, capturing a broader expanse.
• Camera Sensor Size: A larger sensor (e.g., full-frame DSLR) will capture a wider FoV than a smaller sensor (e.g., APS-C or dedicated astronomy camera) when paired with the same telescope.

Knowing your FoV helps you frame your target effectively and decide if your current setup is appropriate for the object you wish to photograph.

What is Image Scale?

Image Scale, often expressed in arcseconds per pixel (arcsec/pixel), tells you how much of the sky's angular dimension each individual pixel on your camera sensor covers. It's a measure of your system's resolution and how finely it can resolve details.

The Image Scale is influenced by:

• Telescope Focal Length: A longer focal length spreads the light from celestial objects over more pixels, resulting in a smaller arcseconds/pixel value (higher resolution).
• Camera Pixel Size: Smaller pixels on your camera sensor will also lead to a smaller arcseconds/pixel value (higher resolution), as each pixel captures a finer detail of the sky.

An optimal image scale is crucial for sharp astrophotography. If your image scale is too high (too many arcseconds per pixel), your image might appear "undersampled," meaning you're not capturing all the detail your telescope is capable of. If it's too low (too few arcseconds per pixel), your image might be "oversampled," leading to larger file sizes and potentially softer images due to atmospheric seeing conditions, without necessarily adding more useful detail.

A common rule of thumb for deep-sky imaging is to aim for an image scale between 1.0 and 2.0 arcseconds/pixel, though this can vary based on your local seeing conditions and specific imaging goals.

How to Use This Calculator:

Simply input the specifications of your telescope and camera into the fields above:

• Telescope Focal Length (mm): This is usually printed on your telescope or found in its specifications.
• Camera Sensor Width (mm): The physical width of your camera's sensor.
• Camera Sensor Height (mm): The physical height of your camera's sensor.
• Camera Pixel Size (microns): The size of an individual pixel on your camera sensor, typically found in the camera's specifications (e.g., 3.76µm, 4.75µm).

Click "Calculate Astrophotography Parameters" to instantly see your Horizontal Field of View, Vertical Field of View, and Image Scale. Use these values to plan your imaging sessions and optimize your equipment choices for different celestial targets.