All Labs

Telescope Resolution & Light Gathering Lab

Adjust aperture, focal length, and eyepiece to see how each parameter affects angular resolution, light gathering power, magnification, and field of view. Compare refractor and reflector designs side by side.

Guided Experiment: Aperture and Resolution

How does increasing the telescope aperture affect angular resolution and light gathering power? What mathematical relationship do you expect?

Write your hypothesis in the Lab Report panel, then click Next.

Optical Path

Refractor80 mm | f/10FocusEyepiece
Resolution: 1.73″LGP: 131×Mag: 80×FOV: 0.63°Exit Pupil: 1 mm

Controls

Telescope Parameters
5010,000
10060,000
440
380700

Results

Angular Resolution
1.73 arcsec
theta=1.22lambda/D\\theta = 1.22\\lambda / D
Dawes Limit
1.45 arcsec
thetaD=116/Dtextmm\\theta_D = 116 / D_{\\text{mm}}
Light Gathering Power
131 ×
textLGP=(D/7)2\\text{LGP} = (D/7)^2
Magnification
80 ×
M=ftextobj/ftexteyeM = f_{\\text{obj}} / f_{\\text{eye}}
Focal Ratio
f/10
f/\\# = f / D
True FOV
0.63 °
textFOV=50°/M\\text{FOV} = 50° / M
Exit Pupil
1 mm
textEP=D/M\\text{EP} = D / M
Limiting Magnitude
11.5 mag
m=2+5log10Dm = 2 + 5\\log_{10}D

Data Table

(0 rows)
#TrialTypeAperture(mm)f-ratioResolution(″)LGP(×)Mag(×)FOV(°)
0 / 500
0 / 500
0 / 500

Reference Guide

Angular Resolution

The Rayleigh criterion defines the smallest angle a telescope can resolve. Two point sources closer than this angle blur together.

θ=1.22λD×206,265  arcsec\theta = 1.22 \frac{\lambda}{D} \times 206{,}265 \;\text{arcsec}

Larger apertures resolve finer details. The Dawes limit (116/D) gives a tighter empirical bound for equal-brightness stars.

Light Gathering Power

A telescope collects light over its full aperture area. Light gathering power compares the telescope to the unaided human eye (7 mm pupil in the dark).

LGP=(DDeye)2=(D7)2\text{LGP} = \left(\frac{D}{D_{\text{eye}}}\right)^2 = \left(\frac{D}{7}\right)^2

Doubling the aperture quadruples the light gathering power, letting you see fainter stars and nebulae.

Magnification & FOV

Magnification depends on the ratio of objective focal length to eyepiece focal length. Higher magnification narrows the field of view.

M=fobjfeye,FOVtrue=FOVappMM = \frac{f_{\text{obj}}}{f_{\text{eye}}}, \quad \text{FOV}_{\text{true}} = \frac{\text{FOV}_{\text{app}}}{M}

Maximum useful magnification is about 2 times the aperture in mm. Beyond that, the image dims and atmospheric turbulence dominates.

Refractors vs Reflectors

Refractors use a convex objective lens to bend (refract) light to a focal point. They give crisp, high-contrast images but large lenses are expensive and suffer from chromatic aberration.

Reflectors use a concave primary mirror to bounce light to a secondary mirror and then to the eyepiece. Mirrors avoid chromatic aberration and scale to much larger apertures at lower cost.

The focal ratio (f/# = f/D) affects image brightness for extended objects. Fast scopes (low f-number) are better for wide-field deep-sky imaging.