Lunar Astrophotography Calculator — Telescope FOV, Plate Scale, Limiting Magnitude

Your equipment & the Moon now

DSLR APS-C + 200 mm @ f/10.2 · Thursday, April 30, 2026 21:00

🌕 Full Moon · 99.4% illuminated · age 14.1 d · mag -12.44

Limiting magnitude

13.4

m_lim = 2 + 5·log₁₀(D_eff)

Plate scale

0.44"

arcsec/pixel

Effective focal ratio

f/10.2

2,032 mm / 200 mm

Effective aperture

187.3 mm

subtracts 70 mm obstruction

Diagonal FOV

54.6'

1.83 Moons

Real resolution

1.50"

limited by seeing

🎯 Field of view (FOV)

Does the Moon fit in frame?

✓ YES

Moon = 29.83' diameter · sensor = 45.4' × 30.3'

Horizontal FOV

45.39'

arcmin (long side)

Vertical FOV

30.26'

arcmin (short side)

FOV in "Moons"

1.83 ⌀M

framing capacity

Field of view diagram

Camera sensor (light rectangle) vs. real Moon size (circle) — to scale.

How to read the diagram:

The turquoise rectangle is your camera sensor (45.4′ × 30.3′).
The light circle is the Moon at correct scale (⌀ 29.83′ ≈ 0.50°).
The Moon fits inside the rectangle — your image captures the entire Moon with margin.

📐 Real resolution (Dawes vs seeing)

Dawes limit

0.58"

116/D mm (theoretical diffraction)

Rayleigh limit

0.69"

138/D mm

Local seeing

1.50"

atmospheric turbulence

Real resolution

1.50"

bottleneck: SEEING (atmosphere)

Sampling: 0.29 px per resolution element · Good sampling

⏱️ Recommended exposure (Looney 11 adjusted)

ISO 100

Time: 1/291 s
f-stop: f/10.2 (from equipment)
Notes: Heavy tripod · remote trigger · live view

ISO 400

Time: 1/1165 s
f-stop: f/10.2
Notes: Good for times < 1/100 s

ISO 1600

Time: 1/4662 s
f-stop: f/10.2
Notes: Useful for young or rising Moon

Looney 11 base: f/11, ISO 100 → 1/250 s for Full Moon. Auto-adjusts to your focal ratio and current phase.

🌑 Features visible at the terminator NOW

Sun colongitude = 262.4°. Selenographic terminator ≈ -172.4°. Features within ±12° have long shadows and prominent relief.

No notable features near the terminator right now. At Full Moon (colong ~0°/180°) the relief looks flat because there are no shadows — best for shooting the bright ray systems of Tycho and Copernicus. In young phases (crescent/last quarter) the terminator crosses the visible face and reveals the relief dramatically.

🌃 Best time to shoot TONIGHT

Moon transit

—

local culmination (highest Moon = best seeing)

Local sunset

20:26

soft sky+moon contrast for ~1 h

Moon altitude now

10.9°

above the horizon (refraction applied)

Optimal imaging window

⚠ LOW

above 30° = thin atmosphere · ideal > 50°

📅 Next 5 best nights for imaging

Full Moon

Date and time (UTC): 2026-05-01 17:23 UTC
In: 0 days
Why it's good: Tycho/Copernicus ray systems showcased

Last Quarter

Date and time (UTC): 2026-05-09 21:10 UTC
In: 8 days
Why it's good: Terminator reveals Aristarchus and Procellarum

First Quarter

Date and time (UTC): 2026-05-23 11:10 UTC
In: 22 days
Why it's good: Terminator at center — dramatic relief on the maria

Full Moon

Date and time (UTC): 2026-05-31 08:45 UTC
In: 30 days
Why it's good: Tycho/Copernicus ray systems showcased

Last Quarter

Date and time (UTC): 2026-06-08 10:00 UTC
In: 38 days
Why it's good: Terminator reveals Aristarchus and Procellarum

🔄 Tracking rate (Moon tracking)

dRA (asec/sec)

0.487

drift in right ascension

dDec (asec/sec)

-0.200

drift in declination

dRA (°/min)

0.0081

conversion to degree/minute

dAlt / dAz

9.11" / 10.78"

altitude / azimuth (asec/sec)

The Moon moves ~13°/day in RA — different from the sidereal rate. Use "Lunar tracking" mode on your controller (Celestron NexStar, Meade AutoStar, EQDirect, etc.) for accurate guiding.

📤 Export coordinates to telescope

Current Moon RA/Dec (13:57:20 / -16:27:16.46) in Goto command formats for the main amateur telescope controllers.

🔭 Meade LX200 (Autostar)

#:Sr13:57:20#
#:Sd-16*27:16#
#:MS#

🛰️ Celestron NexStar

Goto J2000 RA=13:57:20 Dec=-16:27:16.46 | serial: r94DBA512,F44C895C

⚙️ Sky-Watcher SynScan

GOTO RA=13:57:20 Dec=-16°27'16" | ASCOM: 209.331545 , -16.454572

📱 SkySafari (import)

RA:  13:57:20
Dec: -16:27:16.46
Epoch: J2000.0

Coordinates in ICRS / J2000.0 (apparent topocentric for the observer). For sharper alignment: do polar align first and use star alignment on the controller. RA decimal: 209.3315° · Dec decimal: -16.4546°.

📍 Moon position now

Altitude (apparent)

10.94°

above the horizon

Azimuth

123.5°

N=0 · E=90 · S=180 · W=270

Hour angle

-58.36°

positive = west of meridian

Topocentric distance

399,159 km

from observer to Moon

📧 Found a bug? Want to suggest a feature?

Email us at rcgwebsites@gmail.com and please include:

Your equipment specs (aperture, focal length, sensor, pixel size)
What you expected to see vs what you actually saw
Full URL with all parameters
Steps to reproduce (if applicable)
Screenshots are very helpful

We reply within ~5 business days. Suggestions for additional features (telescope models, sensor presets, etc.) are welcome.

How to use the lunar astrophotography calculator

This lunar astrophotography calculator is built for amateur telescope users (Celestron NexStar, Meade LX200, Sky-Watcher 200P/250P, CPC925) or DSLR/mirrorless shooters with a telephoto lens. You enter your equipment and the calculator returns limiting magnitude, plate scale (arcsec/pixel), FOV in Moons, recommended exposure (Looney 11), features visible at the terminator, and the next best night for imaging.

Main inputs

Aperture (mm): mirror/objective diameter. Examples: NexStar 8SE = 200 mm, Meade LX200 8" = 203 mm, Sky-Watcher 250P = 254 mm.
Focal length (mm): e.g. 2032 (NexStar 8SE), 2350 (CPC925), 1200 (Sky-Watcher 250P f/4.7).
Central obstruction (mm): diameter of the secondary mirror in SCT/Newtonian designs. Reduces effective aperture. Example: 70 mm in a 200 mm SCT.
Camera + pixel size + resolution: pick the type (DSLR APS-C, Full-Frame, Mirrorless 4/3, smartphone, dedicated lunar webcam) and the calculator pre-fills typical values. You can edit them.
Seeing (arcsec): local atmospheric turbulence. 1.5" suburban · 1.0" dark site · 2.5" urban. Limits your real resolution.

Computed outputs

Limiting magnitude: m_lim = 2 + 5·log₁₀(D_eff). D_eff = √(D² − D_obstr²). Faintest star detectable visually.
Plate scale (arcsec/pixel): 206264.806 / focal_mm × pixel_size_um/1000. Defines how many arcseconds fit in each pixel.
Real resolution: max(Dawes, seeing). Dawes = 116/D mm. Seeing is almost always the bottleneck.
Diagonal FOV: arcmin of the entire sensor. Compared with the Moon's angular diameter (~31') = how many Moons fit.
Exposure (Looney 11): base = 1/250 s @ ISO 100, f/11 for Full Moon. Adjusted to your focal ratio and current illumination.
Features at the terminator: compares feature selenographic longitudes with current colongitude. Shows craters/maria with prominent relief right now.
Tracking rate: dRA/dDec/sec to configure lunar tracking on your controller.

Why the terminator matters

The terminator is the line between the illuminated and dark sides of the Moon. Craters and maria look most striking near the terminator because long shadows reveal the relief. At Full Moon the terminator is at the limb (edge) and the face appears "flat" — not the best phase for surface detail (but the best one for shooting the bright ray systems of Tycho and Copernicus). At First/Last Quarter the terminator crosses the center of the visible face and reveals relief dramatically.

Which telescope is this calculator for?

Any amateur telescope between 80 mm and 400 mm of aperture. Optimized for Schmidt-Cassegrain (Celestron NexStar 6SE/8SE/9.25/11, Meade LX200 8"/10"/12"), Newtonian reflectors (Sky-Watcher 130P, 150P, 200P, 250P) and ED refractors (80 mm, 100 mm, 120 mm). It also works for DSLR telephoto lenses (Canon 800 mm, Nikon 600 mm) with an adapter.

Frequently asked questions

How does the lunar astrophotography calculator work?

You enter aperture, focal length, sensor (pixel size + resolution) and local seeing. The calculator returns limiting magnitude (faintest detectable stars), plate scale (arcsec/pixel), FOV (field of view in Moons), recommended exposure (Looney 11), features visible at the terminator right now, and the next best night for imaging.

What is the terminator?

The terminator is the line between the illuminated and dark sides of the Moon. Craters and maria look most striking near the terminator because long shadows reveal the relief. At Full Moon the terminator is at the limb (edge) and the face appears "flat" — not the best phase for surface detail.

Is my telescope good enough for the Moon?

For the Moon, any 80 mm+ telescope already produces a spectacular image. The limiting factor is local seeing (atmospheric turbulence): even a 200 mm+ Schmidt-Cassegrain will not resolve detail finer than 1-2 arcsec under poor seeing. The calculator shows whether the bottleneck is diffraction or seeing.

What is "Looney 11"?

It is the rule of thumb for photographing the Moon: f/11, ISO equal to the denominator of the exposure. For Full Moon: f/11, ISO 100, 1/100s. The calculator adjusts the formula for your focal ratio and the current phase.

Does the calculator work for modern DSLR and mirrorless cameras?

Yes. Pick the type (DSLR APS-C, Full-Frame, Mirrorless 4/3, smartphone, dedicated webcam) and it pre-fills typical pixel size and resolution. You can edit the values manually if your camera differs.