Camera Slate

Add accurate timestamps and GPS coordinates to photos from cameras without built-in GPS by photographing the Camera Slate screen.

What You’ll Learn

• How to record verified time and location data for your photo shoots
• How to use the Camera Slate to correct timestamps in post-processing
• How to manually geotag photos using coordinates from the slate
• How to time astronomical events like eclipses, transits, and occultations
• How to interpret the accuracy indicators

The Problem Camera Slate Solves

Most DSLR and mirrorless cameras don’t have built-in GPS. This means:

• Photo timestamps rely on the camera’s internal clock, which drifts over time
• Photos have no embedded location data (latitude, longitude, elevation)
• When reviewing images months later, you may not remember exactly where you shot them

The Camera Slate turns your iPhone into a portable reference device. Photograph the slate screen with your main camera at key moments during a shoot. Later, when you import your images, you can:

1. Correct timestamps by comparing your camera’s recorded time against the NTP-verified time shown on the slate
2. Manually geotag photos using the precise coordinates displayed on the slate
3. Reference the QR code to quickly extract time and location data

Opening Camera Slate

1. Open TPE and tap the menu
2. Select Camera Slate

The slate displays three main sections: time, location, and a QR code.

Understanding the Display

Time Section

The time section shows:

• Date: Current date in your local time zone
• Time: NTP-verified time with centisecond precision (e.g., 14:32:45.67)
• Timezone: Your current timezone with UTC offset and DST indicator

A small colored dot next to the time indicates sync status:

Color	Meaning
Green	NTP-verified time — your device has synced with network time servers
Yellow	Syncing in progress, or offline (using device clock)
Red	Sync failed — using device clock, may be inaccurate

Location Section

The location section shows:

• Coordinates: Latitude and longitude in decimal degrees (e.g., N 45.52381°, W 122.67563°)
• Elevation: Height above sea level in your preferred units
• Heading: Compass direction you’re facing, with cardinal point (e.g., 285° WNW)

Each measurement has a colored accuracy indicator:

Color	Location Accuracy	Meaning
Green	Excellent	< 10 meters
Yellow	Good	10-30 meters
Orange	Fair	30-100 meters
Red	Poor	> 100 meters
Gray	Unknown	No GPS fix

A status badge appears when there’s a location issue:

• Searching: Acquiring GPS signal
• Weak Signal: GPS accuracy is degraded
• Moving: You’re in motion (useful context for accuracy)
• Unavailable: No GPS available

QR Code Section

The QR code encodes the current timestamp and coordinates in a machine-readable format. It automatically refreshes:

• Every 10 seconds
• When you move more than 10 meters
• When you tap the refresh button

The age counter below the QR code shows how many seconds have elapsed since the code was generated (e.g., +07.23s).

Using Camera Slate in the Field

Basic Workflow

1. At the start of your shoot: Photograph the slate with your camera
2. When you move to a new location: Photograph the slate again
3. At the end of your shoot: Take a final slate photo

This gives you reference points for timestamp correction and geotagging.

Photographing the Slate

For best results:

1. Hold your phone steady with the slate screen facing your camera
2. Fill enough of the frame that all text is readable
3. Use a shutter speed fast enough to freeze the display (the time updates every centisecond)
4. Wait for green accuracy indicators when possible

When to Capture a Slate Photo

• Start of shoot: Establishes your baseline timestamp offset
• Each new location: Provides coordinates for that group of photos
• After significant time passes: Camera clock drift can accumulate
• End of shoot: Confirms final timestamp reference

Post-Processing Workflow

Correcting Timestamps

1. Import your photos and find the slate image
2. Compare times: Note the timestamp your camera recorded for the slate photo and the time displayed on the slate screen
3. Calculate the offset: If the slate shows 14:32:45 but your camera recorded 14:31:23, your camera is 1 minute 22 seconds slow
4. Apply the correction: Use your photo management software to shift all timestamps by this offset

Most photo management applications (Lightroom, Photo Mechanic, etc.) can batch-adjust timestamps.

Geotagging Photos

1. Find each slate photo in your import
2. Note the coordinates displayed on the slate
3. Apply to nearby photos: In your photo management software, set the GPS coordinates for photos taken at that location

For the QR code:

1. Scan the QR code with your phone’s camera or a QR reader
2. The encoded time and coordinates can be copied directly into your geotagging workflow

Timing Astronomical Events

The Camera Slate’s NTP-verified timestamps are useful for timing high-speed astronomical events, allowing you to compare your observations against published predictions.

Use Cases

• Solar eclipse contacts: Capture the precise moments of second contact (C2, when totality begins) and third contact (C3, when totality ends)
• Lunar transits: Time the moment the International Space Station or other satellites cross the lunar disk
• Lunar occultations: Record when the Moon occults (passes in front of) planets like Jupiter, or bright stars

Workflow for Event Timing

1. Before the event: Photograph the Camera Slate to establish your camera’s time offset
2. During the event: Capture your images normally with your camera
3. After the event: Photograph the slate again to confirm the offset hasn’t drifted
4. In post-processing: Apply the offset correction to your event images, then compare your corrected timestamps against predictions

This lets you verify whether an event occurred at the predicted time, or measure the actual time difference between prediction and observation.

Important Limitations

Camera Slate provides timing accurate to approximately ±50-100 milliseconds under good network conditions. This is sufficient for:

• Comparing your photos against eclipse contact predictions (typically accurate to ~1 second)
• Verifying ISS transit timing (events lasting 1-2 seconds)
• General astronomical event documentation

However, Camera Slate is not a replacement for high-accuracy timing equipment required for scientific observation of occultations. Serious occultation work — such as measuring asteroid sizes or detecting binary stars — requires dedicated GPS-synchronized timing devices with millisecond or sub-millisecond accuracy.

For information on proper timing equipment and techniques for occultation observation, see the International Occultation Timing Association (IOTA).

Viewing Accuracy Details

Tap any of the colored accuracy indicators to open the Accuracy Detail sheet. This shows:

Time Sync Status

• NTP Verified: Your device has synchronized with network time servers
• System Clock (Offline): No network available; using device clock
• System Clock (Sync Failed): Network available but sync failed; device clock may be inaccurate

When NTP is available, you’ll also see the System Clock Delta — how far your device’s internal clock differs from true time (e.g., “ 42 ms fast ”).

Tap Re-sync Time to force a fresh NTP synchronization.

Location Accuracy

• Horizontal: How accurate the latitude/longitude is (radius of uncertainty)
• Vertical: How accurate the elevation is
• Heading: How accurate the compass direction is

Accuracy levels:

Level	Horizontal/Vertical	Heading
Excellent (green)	< 10 m	< 15°
Good (yellow)	10-30 m	15-30°
Fair (orange)	30-100 m	30-60°
Poor (red)	> 100 m	> 60°

Improving Accuracy

For better GPS accuracy:

• Move to an area with a clear view of the sky
• Wait 30-60 seconds for the GPS to acquire more satellites
• Avoid standing near tall buildings or under dense tree cover

For better compass accuracy:

• Move away from magnetic interference (cars, electronics, metal structures)
• Calibrate by moving your device in a figure-8 pattern
• The compass icon rotates to show your current heading

For better time accuracy:

• Ensure you have network connectivity (WiFi or cellular)
• Tap Re-sync Time in the Accuracy Detail sheet
• Green indicator confirms NTP synchronization

Tips

• Photograph the slate at eye level: This makes the QR code easier to scan later
• Include some context: Consider including a landmark or sign in the frame alongside the slate to help you remember the location
• Check accuracy before shooting: Wait for green indicators when documenting critical locations
• Use airplane mode strategically: If you need to conserve battery but want slate photos, open Camera Slate before enabling airplane mode — it will continue using the last known location

Related Features

• Night Sky Exposure — Plan long exposures for astrophotography

Learn More

For technical details about NTP time synchronization and GPS accuracy, see Camera Slate - Technical.