Longlight

Longlight Support

Help with capturing, saving, and managing long-exposure photographs in Longlight (慢光).

Frequently Asked Questions

Why combine short exposures?

An iPhone's single-exposure limit is approximately one second. Longlight combines many short exposures on your device so that motion and changing light can build up into a long-exposure photograph.

Which capture mode should I choose?

Use "Star Trails" for the movement of stars, "Light Trails" for moving lights, and "Silky Water" for flowing water. "Light Painting" is for drawing with light, and "Night Scene" is for night photography. Choose "Manual" when you want to set the capture parameters yourself.

How should I prepare a shot?

Place the device on a stable tripod and compose the image before starting a long capture. Use "Test frame" and its assessment to review the capture settings. Adjust the setup or settings and repeat "Test frame" as needed.

How do I finish a capture?

For "Star Trails" and the other long-capture modes except "Light Painting", press and hold the on-screen shutter to finish. In "Light Painting", tap the shutter to finish. With a volume button, Camera Control, or a Bluetooth remote shutter, press once to save a snapshot, or press twice within 1.5 seconds to finish the capture.

What if a call, app closure, or depleted battery interrupts capture?

Longlight saves a checkpoint every minute. Open the App again to recover from the saved checkpoint. Recovery uses the saved checkpoint, so it may not include the part captured after that checkpoint.

How can I remove unwanted headlights?

During capture, "Undo last minute" appears after one minute of shooting; use it if unwanted headlights appeared in the most recent minute. If you enabled "Keep every frame" for the capture, open the work in "Captures", select the minutes to exclude, and tap "Re-stack".

Where are my works saved, and which formats can I export?

Works are stored in "Captures" and in Files under "On My iPhone › Longlight"; "Save finished photos to Photos" is on by default and can be turned off in "Settings", and saving requires permission. Outputs include HEIF, 16-bit TIFF, single-frame DNG on supported devices, and growth videos; deleting an App work does not delete separate Photos or exported copies. Finished photographs (HEIF), previews, 16-bit TIFF files, work reports, and work information enter system iCloud or computer backups according to your backup settings. The App marks retained source frames, growth videos, and recovery checkpoints as excluded from system backups.

What are "Red interface" and "Dark screen" for?

"Red interface" makes the controls suitable for use in a dark environment with less bright screen light. "Dark screen" reduces the screen light during a capture. Choose the display mode that suits your shooting conditions.

What happens if the device gets hot or runs low on power or storage?

Long captures use power and storage and can warm the device. Longlight's resource guards provide reminders and save capture progress when heat, battery level, or available storage becomes a constraint. Check power and free space before starting, especially when using "Keep every frame".

Does Longlight need an internet connection or send my data?

The App works on your device and establishes no network connections; the Developer receives no data from within it. It is free, advertising-free, and usable without an account. Diagnostic files reach us only if you choose to share them with us, while Apple's optional system analytics sharing can provide aggregate crash and usage statistics separately.

How is location used, and which setting is off by default?

Location is optional and can be used to calculate twilight periods and moon phase in "Tonight"; you can enter latitude and longitude manually instead. "Write location into photos" is a separate setting and is off by default. When enabled, it writes location into photo metadata. The App processes location on the device and does not keep a route history; a photo you share can carry its included metadata.

Which devices are supported?

Longlight runs on iPhone and iPad with iOS or iPadOS 18 or later and is distributed through the Apple App Store. Single-frame DNG export requires a supported device. Camera Control and remote shutter operation depend on the corresponding hardware or accessory.

How can I send diagnostic information?

Open "Settings" › "Diagnostics" › "Share diagnostics log"; for a capability report, select "Write capability report" and then "Share capability report", and choose your destination. To send it to support, address an email to longlight@gacing.com. The diagnostic materials include device, system, and camera capability information and contain no photos, location, or personally identifying information. We receive only the copy you send; your email address and message are part of the support correspondence.

Contact Support

Contact GACING at longlight@gacing.com. Describe what happened and the steps that led to it. Include the diagnostic log and capability report when reporting a technical problem so that the device and camera context can be reviewed.

Under "Settings" › "Diagnostics", use "Share diagnostics log", or "Write capability report" followed by "Share capability report", and select the email or other destination yourself. Review any additional images or files before attaching them, including location metadata in photographs. The Privacy Policy explains how support correspondence is handled.

Release Notes

1.0 (October 2026)