Image Circle Checker
Check if your camera sensor fits within your optic's image circle. If the sensor is larger, you'll see vignetting (dark corners) in your images.
Camera Sensor
Optic
Common values: 28mm (APS-C), 44mm (full frame), 60mm+ (medium format)
Visual Comparison
Image Circle (44mm)
Sensor (28.3mm diagonal)
Coverage
156%
Full Coverage
Sensor Diagonal
28.3mm
Image Circle
44mm
Good Match
Your sensor fits well within the image circle. You should have full illumination across the entire frame with no vignetting.
What is Image Circle?
The image circle is the circular area where your telescope or lens produces a sharp, evenly illuminated image. Outside this circle, light falls off (vignettes) or shows optical aberrations.
Your sensor must fit entirely within the image circle to avoid dark corners. The sensor diagonal (corner-to-corner distance) is what matters, not just width or height.