Photogrammetry Photography Guide: Ring Flash Photography

Journalism Technologist Ben Kreimer prepared a complete guide to photogrammetry photography for Journalism 360. We’ve shared portions of the guide, Shooting Underneath Objects and Ring Flash Photography, here with their permission. Join Ben for a virtual Q&A on May 21, 2020, to learn about all things photogrammetryThe use of photography to survey and map a location from a variety of angles..

A Linear Polarized Ring Flash

A 400 W/s ring flash battery-powered ring flash is a powerful tool for photogrammetryThe use of photography to survey and map a location from a variety of angles. in situations where ambient is low, or non-existent. It’s unbeatable for quickly and evenly lighting objects. With its intensity, you can easily shoot at f/16 or higher on your camera’s lowest ISO setting. Plus it’s a very portable lightsource as opposed to lights and stands, which bring shadow challenges because the object has to be completely and evenly lit.

The ring flash is useful in many indoor environments where the ambient lighting is suitable for human eyes, but requires a camera to shoot at high ISO settings to make it possible to shoot at a high f/stop for photogrammetryThe use of photography to survey and map a location from a variety of angles.. Most importantly, the portability of the ring flash enables you to quickly illuminate surfaces in hard to reach areas, as demonstrated on the right.

To maximize the utility of the ring flash, attaching a linear polarizing gel over the flash, along with a circular polarizer on the lens, will prevent the flash burst from reflecting off surfaces and appearing in your photo. This is essential for surfaces that reflect light, and makes it possible to shoot through plexiglass and glass. This polarized ring flash setupA camera position for a given scene. You might shoot more than one shot from a single set-up (wide shot and close-up). allows you to capture the undersides of objects placed on plexiglass, and when the occasion arises, to do photogrammetryThe use of photography to survey and map a location from a variety of angles. photography through glass.

The images of a lemon, avocado, and wood surface, demonstrate the effect of polarization when using the ring flash. The image on the left was captured with the ring flash, but without the linear and circular polarizing filters. The image on the right was captured using identical settings on the camera and ring flash power setting, but with the polarization filters.

Buying a Ring Flash

The Godox Witstro AR400 and Flashpoint Ring Li-On ring flashes (top row at right) have different labeling but both contain the same components and specifications, including a 400Ws flash bulb and LEDs. They are suitable for small to large-scale indoor object and small room capture photogrammetryThe use of photography to survey and map a location from a variety of angles.. This is all the flash you need for doing indoor object photogrammetryThe use of photography to survey and map a location from a variety of angles., even if the space is pitch black. When using the Ring Li-On, I consistently shoot at 200 ISO, f/16, 1/200th of a second and get, even if the room is pitch black.

I don’t recommend other ring flash hardware, or ring lights (bottom row at right). The ring light, with it’s LED halo, is a constant light source, and provides a light glow but lacks the lighting power of a more powerful flash. The low power ring flash on the right is designed for macrophotography, and will not be suitable for non-macro imaging. The majority of ring flashes available are in this small, macro form factor, and they should be avoided, unless you’re doing macro-photogrammetry.

Linear and Circular Polarization

You cannot buy a gel holder for these ring flashes. I bought a linear polarizing sheet, cut the gel to the shape of the flash, and used gaffers tape to attach the linear polarizer filter to the ring flash. It looks rough but performs perfectly.

What you need:

An A4-sized (approximately 8.5” x 11”) linear polarization gel that fits over the ring flash. Buy two sheets, in case you mess up the first attempt because the sheet tears easily.
Gaffers tape
A circular polarizer filter that fits your lens. The B+W XS-Pro Kaesemann High Transmission Circular Polarizer MRC-Nano Filter works well.
A PC sync port adapter if your camera doesn’t have the port built in, such as a Wein Products Safe-Sync Hot Shoe to Hot Shoe adapter that has a PC sync port (pictured below in center).
The male to male PC sync cable that comes with the ring flash.

Recommended Accessory:

A quick release adapter with mounting plateA part of a composite, usually intended as a background, though here it refers to a duplicate version of the main shot w... More that corresponds to the tripod make and model you use. This is essential for speeding up the attachment and removal of your camera from the ring flash mounting bracket. Without the adapter you’ll have to center your camera in the ring every time you attach it to the ring flash. Seen here at right is the Manfrotto 323 RC2 Rapid Connect Adapter with Quick Release PlateA part of a composite, usually intended as a background, though here it refers to a duplicate version of the main shot w... More.