Enter the pixel size (µm) and the focal length (mm) into the Calculator. The calculator will evaluate the Arc Seconds Per Pixel.
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Arc Seconds Per Pixel Formula
ASPP = (PS/FL) * 206.265
Variables:
- ASPP is the Arc Seconds Per Pixel (arc-sec/pixel)
- PS is the pixel size (µm)
- FL is the focal length (mm)
To calculate Arc Seconds Per Pixel, divide the pixel size by the focal length, then multiply by 206.265.
How to Calculate Arc Seconds Per Pixel?
The following steps outline how to calculate the Arc Seconds Per Pixel.
- First, determine the pixel size (µm).
- Next, determine the focal length (mm).
- Next, gather the formula from above = ASPP = (PS/FL) * 206.265.
- Finally, calculate the Arc Seconds Per Pixel.
- After inserting the variables and calculating the result, check your answer with the calculator above.
Example Problem :
Use the following variables as an example problem to test your knowledge.
pixel size (um) = 75
focal length (mm) = 90
Frequently Asked Questions
What is an Arc Second?
An arc second is a unit of angular measurement equal to 1/3600th of a degree. It is commonly used in astronomy to describe the apparent sizes of celestial objects and the precision of telescopic observations.
Why is the Arc Seconds Per Pixel (ASPP) important in astronomy?
ASPP (arc-sec/pixel) describes the image scale (how much sky each camera pixel covers). It is commonly used to understand how finely an imaging system samples detail and to help match a camera/telescope setup to typical seeing conditions.
Can the Arc Seconds Per Pixel value affect the quality of astronomical images?
Yes. A lower ASPP value means each pixel covers a smaller angle on the sky (finer sampling), which can capture more detail if the optics and atmospheric seeing support it. A higher ASPP value means each pixel covers a larger angle (coarser sampling), which captures less fine detail but can provide a wider field of view and higher signal per pixel.
How does changing the focal length of a telescope affect the ASPP?
From ASPP = (PS/FL) × 206.265, ASPP is inversely proportional to focal length. Increasing the focal length decreases the ASPP value (smaller arc-sec/pixel; finer sampling). Reducing the focal length increases the ASPP value (larger arc-sec/pixel; coarser sampling).
