Crime scene photography using off-the-shelf gear: Part 2
How lenses, lighting and color balance achieve the most accurate representation of in situ evidence
In part one of this three-part series, I covered why color and accuracy of photos taken at a crime scene are important and how differences in lighting can change the color of evidence.
In this second installment, I will cover the types of lenses, lighting and color balance required to achieve the most accurate representation of in situ evidence.
Whether for a camera or a smartphone, lenses should be of high quality with minimal or no chromatic or optical aberrations, which can taint your photos. Examples of lenses that could be in your kit include macro or close-up, fisheye, wide-angle, normal, telephoto and perhaps an anamorphic lens for taking overall photos with limited distortion.
The angle of view and magnification of a lens is described by its focal length, which is expressed in millimeters or mm. The longer the focal length, the narrower the angle of view and the higher the magnification. The shorter the focal length, the wider the angle of view and the lower the magnification.
The focal length that you want for each of your lenses will depend on the type of camera you are using – a 58mm lens for a smartphone cannot be compared to a 58mm lens for a full-frame camera.
I use high-quality optical glass lenses from Moment. They are compatible with many smartphones by using a standard mounting system that works with cases designed for dozens of devices from Apple, Google, Samsung and OnePlus.
Modern smartphones have multiple optical sensors and mounting a large Moment lens over one of them blocks the others. To get around this problem, Moment built a camera app for iOS, which lets you manually select the sensor and which lens is mounted on it. With this info, their app performs some optical magic to ensure an undistorted image.
An extensive manual is available, and they also offer a 10-day emailed course. The Moment app is not available for Android due to the substantial number of differences between smartphones that run that operating system so they recommend the Filmic Pro app.
Using an anamorphic lens is a special case. While normal lenses only have spherical elements, anamorphic lenses have an additional vertical cylindrical element. This element compresses the image from left to right onto the sensor to produce a wider image after decompression, so software is required to expand it before it can be viewed. Each anamorphic lens design needs its own expansion algorithm.
Most of Moment's lenses work well when paired with the stock camera application on any smartphone, and anamorphic shots can be de-squeezed with many desktop photography apps.
While they are my lenses of choice, the Moment lenses do have some drawbacks. The 10x macro lens has a very short focusing distance of 0.73" and I have yet to find a way to mount my smartphone that close to an object on the ground to keep it steady while using it. You might need to balance your phone on a notebook to keep it steady. But if an object is near the edge of a table, then a standard floor tripod should work.
Another drawback is finding a pocketable case for a set of lenses. While each lens comes in a small drawstring pouch, Moment doesn’t offer small yet protective multi-lens cases. I am using a Berry VL-40 40 dram “friendly and safe” pill bottle from my local pharmacy, which perfectly stacks 3 lenses, and the 60-dram version can stack 4 or 5 lenses, but that’s not the ultimate solution.
And while each comes with a protective front lens cap, the back is open which can allow dust to get in. Rear lens caps are another $10 each.
Color standard and output calibration
In part 1, several photographs of color calibration panels were shown under different lighting conditions. Even if you didn’t view those images using a calibrated display or printer, you should have been able to tell the difference between them. The perceived color differences are due to the light spectrum under which they were photographed.
Your department should adopt a color temperature standard for forensic photography. Two best bets are noon daylight (often ballparked at 5500-5600K) or cloudy daylight (6000K-6500K) as these two temperatures are as close to “natural light” as possible. Monitors and printers calibrated to the same standard also are required so that photos used as evidence appear as close to the originals as possible.
Although written for specific products, the SpyderCHECKR and ColorChecker Passport manuals will give you an idea of what needs to be done to calibrate your entire workflow. Both companies make high-quality products and which one your department decides to use can depend on several factors, including size, price and availability.
If you purchase and register an X-rite product, such as the Passport Photo 2, you get access to a free application that can make DNG camera profiles. These profiles work with Photoshop and Photoshop Elements, or any other application that supports the Adobe RAW format, to color balance photos taken under the same lighting conditions.
Monitor color calibration compares your monitor to an accepted standard so that there will be consistency in how images are seen. If all monitors are calibrated, a photo should look the same regardless of what screen it’s shown on. Monitors should be calibrated when first purchased and at fixed intervals since the output changes over time.
Calibration of your printer also is essential since printed evidence most likely will be used in court. You can start with the ICC profile for your printer, which corresponds to a specific printer model and paper pair and tweak it using printer calibration tools. Many companies make monitor and printer calibration tools and comparisons between them are available on the internet.
As discussed in Part 1, high-CRI (color rending index) lighting is essential to capture the true colors of both the scene and your evidence. An Internet search will come up with hundreds of options, from bare bulbs or tubes to multi-thousand-dollar lights designed for TV and movie production.
Aputure, a manufacturer of high-end photographic lighting for professionals, has introduced a low-cost pocketable light called the MC. These lights offer a CRI (color rendering index) of 96 out of 100 and can be purchased individually or in kits of 4 or 12 units. The lights have a rotary control wheel and a display on them which allows the selection of color temperature or Hue, Saturation and Intensity (HSI), or stock and custom-built special effects such as paparazzi, faulty bulb, lightning, fire and flashing cop car or fire truck.
Each light has a strong magnetic back and a standard ¼” tripod thread for mounting. The magnets also hold the lights in place inside the kit and each position is a wireless charger. Two lights in the MC-4 kit or three lights in the MC-12 can be connected to the internal 12v/5A outlets using the included cables if you need a faster charge. They also can be charged with the same wireless charger you use with your smartphone. Although the MC light has a USB-C connector, it may or may not charge when connected to USB-C laptops or power supplies.
Table 1: Differences between the MC kits
Your CSI team can toss an MC-4 or MC-12 kit into their vehicle so that they always have access to calibrated lighting when they arrive on scene.
Agencies without a dedicated CSI team might keep a kit in a supervisor’s vehicle or back at the station.
Besides the number of lights, the kits have other differences which you can see in Table 1. While the MC-12 has a built-in accessory drawer, the MC-4 case holds the accessories in a separate bag which you need to keep track of.
The MC-12 case supports the D-Tap power standard, which is used for photography and video production. Power supplies, batteries, cables and gear all are widely available – including the Bescor CIGDTAP 12v cigarette lighter cable. The case can be kept ready for use by charging it in your vehicle, although the lid needs to be open for sufficient cooling.
The MC-4 uses a “pregnant snake” AC power adaptor which connects to a proprietary input jack on the case. Aputure says that an adaptor cable will be available allowing the MC-4 kit to be D-Tap powered, but there is no delivery date.
Without going too far down the rabbit hole, a key capability of many Aputure lights is their support for Sidus Link, a smartphone and tablet app that allows for control of hundreds of lights separately, together or in groups. You can turn lights on and off, dim them, set them to a specific temperature, or because they also can supply light in just about every color imaginable, duplicate the lighting present inside of a bar, restaurant or disco. Using the cloud, light setups on one device can be shared with other devices. This could help your case if you need to re-create crime scene lighting in a lab or courtroom, or to match evidence to the colors described in witness statements.
For example, a witness might describe the color of a piece of evidence that makes no sense. Sidus Link’s source match and color match modes allow you to dial in a specific type of light source or to capture colors from a location and bring them back to the office. MCs then can be used to show a witness a piece of evidence under the original lighting conditions for them to identify before showing it to them again under white light.
MC light flexibility
While not CSI-related, the MC lights also offer a handful of built-in special effects that can be used on your firearms range for low-light training – also controllable via Sidus Link. Some of the more useful effects are the red and blue of a cop car, the red and white of a fire truck, lightning and random camera flashes. By setting multiple lights on different patterns, you can create the same confusion that can occur in real life making training that much more realistic. If you don’t like any of the built-in effects, Sidus Link will let you create your own. MC lights also can be used for your social media projects and online meetings, perhaps making them easier to justify during budget season.
Locate and mark your evidence then before anything is moved, it’s time for lights, camera, action! – followed by cataloging and transport back to base. Without accurate lighting and sharp photography that places each piece of evidence in context (as described in the FBI Academy’s Fundamental Principles and Theory Of Crime Scene Photography), witnesses may not be able to reconstruct the scene in their head nor properly identify or recognize evidence at all. And without photos showing whatever side was up, along with any markings, your lab techs might have trouble reconstructing the events as they occurred.
Part 3 will wrap up showing how modern relatively inexpensive software and hardware can be used to take the different "range" photographs recommended by the FBI Academy document, and how evidence should be marked for photography to make life easier for the techs who process evidence in the lab and the detectives who need to re-create the scene.