Telescope Magnification Worksheet
Goal: Calculate magnification, exit pupil, field of view and resolution, and choose a sensible telescope and eyepiece for a target.
What to do
- Start with the default setup: Telescope focal length 1,000 mm, Eyepiece focal length 25 mm, Aperture 100 mm and Eyepiece apparent field 60°. Record the readouts.
- Change only Eyepiece focal length to 10 mm and record the readouts.
- Press each preset (“Wide view”, “Lunar detail”, “8-inch Dobsonian”) and record its readouts.
Record your results
| Setting | Magnification | True field | Exit pupil | Dawes’ limit | Max useful power |
|---|---|---|---|---|---|
| Default (1,000 mm, 25 mm eyepiece) | |||||
| Default with a 10 mm eyepiece | |||||
| Wide view | |||||
| Lunar detail | |||||
| 8-inch Dobsonian |
Questions
How do you calculate magnification? Check your rule with the default setup.
When you swapped the 25 mm eyepiece for a 10 mm one, what happened to the magnification, the true field and the exit pupil?
The full Moon is about 0.5° across. Which preset shows the whole Moon with the most room to spare? Which preset makes the Moon fill the entire view?
A box says a small 60 mm telescope (700 mm focal length) gives “175× power” with a 4 mm eyepiece. Enter it in the lab. Is that a useful magnification? Explain.
Which preset can split the closest double stars? Use Dawes’ limit to explain.
Why must you never look at the Sun through a telescope without a proper solar filter?
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