What is the ideal pixel scale?

About one-third to one-half of the local seeing (FWHM of star images). For 2-arcsecond seeing, aim for 0.7 to 1.0 arcsec/px.

What happens if pixels are too large?

You under-sample the image, losing detail. Stars appear blocky and fine structure is blurred.

You over-sample: the extra resolution is wasted on seeing blur, while read noise and longer exposures increase.

Determine the angular size each pixel subtends on the sky: pixel_scale = 206.265 * pixel_size / focal_length arcseconds per pixel.

Pixel Size

Focal Length

Pixel Scale

0.7735 arcsec/px

Pixel Scale (arcmin/px)0.012892 arcmin/px

Pixel Scale vs Pixel Size

Pixel scale tells you how much sky each pixel of your camera sensor covers.

pixel_scale = 206.265 * p / f

*p* = pixel size in micrometres

*f* = focal length in mm

206.265 is the conversion factor from radians to arcseconds (with the mm/um unit adjustment)

A good rule of thumb is to match pixel scale to about half the typical seeing (e.g., 1 arcsec/px for 2-arcsecond seeing).

3.75 um pixels on a 1000 mm telescope.

Field of view of the sensor.

Pixels across the field.

Effective focal length with Barlow.