1) What pixel scale measures
Pixel scale tells you how much sky one pixel covers, usually in arcseconds per pixel. Smaller values capture finer detail, while larger values give a wider view and brighter signal per pixel. Imaging goals, target size, and local atmosphere all influence the best choice.
2) Why the 206.265 factor appears
The calculator uses 206.265 because 1 radian equals 206,265 arcseconds, and pixel size is often in micrometers while focal length is in millimeters. Combining those unit conversions yields a compact constant that is widely used in astrophotography planning.
3) Worked example with real numbers
Suppose your telescope is 800 mm and your camera pixels are 3.76 µm. The scale is 206.265 × 3.76 ÷ 800 = 0.969 arcsec/pixel. With a 6248 × 4176 image, your field of view is about 100.9 × 67.4 arcmin, which fits many nebulae comfortably.
4) Seeing and sampling guidance
Atmospheric seeing often ranges from ~1.5 to 3.5 arcseconds for many locations. A practical guideline is 2–3 pixels across the seeing disk, which corresponds to about seeing/2 to seeing/3 arcsec per pixel. The optional seeing input estimates a suggested pixel scale and flags under- or over-sampling.
5) Typical pixel scale targets
For wide-field nebula work, many imagers choose roughly 2.0–4.0 arcsec/pixel to maximize sensitivity and framing. For galaxies and small targets, 0.4–1.5 arcsec/pixel is common, depending on guiding accuracy and seeing. Planetary imaging often uses much finer sampling with different techniques.
6) How focal length changes results
Pixel scale is inversely proportional to focal length. Doubling focal length halves the arcseconds per pixel. For example, keeping 3.76 µm pixels and moving from 400 mm to 800 mm changes scale from about 1.94 to 0.97 arcsec/pixel. This directly impacts resolution and field of view.
7) Pixel size and sensor considerations
Larger pixels increase arcseconds per pixel and can improve per-pixel signal, but may lose fine detail. Smaller pixels reduce scale, which can help resolve structure if your seeing and tracking support it. Sensor width and height control total field of view; the sensor mode estimates FOV from physical dimensions.
8) Using the tool for planning
Start by computing pixel scale from focal length and pixel size. Next, estimate your field of view using either resolution (pixels) or sensor dimensions (mm). Finally, compare the scale to typical seeing and your guiding performance. Export CSV for notes and PDF for project logs or equipment profiles.