SAE International is hosting a FREE Accident Reconstruction Digital Summit on March 29 and 30, 2022. There will be presentations on a wide variety of current issues and areas of interest to anyone working in or with accident reconstructionists, including law enforcement, engineers, attorneys, and insurance adjusters.
From 1:45 to 2:15 pm EDT on Wednesday, March 30, I’ll be presenting on the importance of using a tripod, a polarizer, and a flash during inspections in the field, in storage facilities, and in the lab. The use of those tools can result in superior images—in the camera—with detail and data you can’t extract or replicate later in post-production. Best of all, you can put those three tools to work immediately, which will make your photographs consistently better and more useful.
By the way, my presentation will be just a snippet of what we’ll cover in my three-day SAE Forensic Photography class. Now that SAE will be resuming in-person classes this summer, I’ll post the next class dates as soon as they are finalized.
Eugene Liscio, 3D Forensic Analyst and founder of ai2-3D, has assembled the first virtual Forensic Photography Symposium to be held January 17-20, 2022. There are many intriguing and helpful sessions each day with ideas and solutions to many problems often encountered in many areas of forensic photography. Here’s a link to the schedule and registration: Forensic Photography Symposium Schedule & Registration
I’ve been honored to have been asked by Eugene to present a session on the three most essential photography tools besides your camera and lens. They are: tripods, polarizer filters, and flashes. Most forensic photographers know what those tools are, but this presentation is designed to explore and show examples of how their regular use can drastically improve the quality and usefulness of your images. Using these tools, you will be able to consistently capture and present more data in each of your images, which is the whole point of making forensic photographs!
Screenshot from YouTube Intro for Forensic Photography Symposium January 17-20, 2022.
While this is hardly news, on sunny or lightly overcast days, the positions and sizes of the shadows of trees, buildings, signs, poles, fences, guardrails, etc., change throughout the day. At certain times, these shadows can make it difficult to clearly show tire marks, paint marks, or gouges in your photographs. The worst is when there is a pattern of light and shadow across your scene.
This first image was made at 10:21 am on a mostly sunny morning. (Click on image to enlarge. Then click back arrow to return to this post.)
Tree shadows at 10:21 am on 09/04/21. (Made with ZEISS 50 mm f/2 macro lens on Nikon D850 on RRS TFC-24L tripod with BH-40 ball head. f/11, 1/8 sec, ISO 64.)
This view was made looking south, so the morning sun would have been to left, or east. The dense line of trees on the eastern edge of the road cast a shadow across the entire road with bright spots through the openings in the branches. These bright spots can interfere with details or evidence you might want to show.
Returning to that same scene at 2:45 pm that afternoon, the overcast had burned off. Even though the sun was quite bright, it was at an angle that evenly illuminated a lot more of the road, with only some shadows at the left. (Click on image to enlarge. Then click back arrow to return to this post.)
Tree shadows at 2:44 pm on 09/04/21. (Made with ZEISS 50 mm f/2 macro lens on Nikon D850 on RRS TFC-24L tripod with BH-40 ball head. f/11, 1/60 sec, ISO 64.)
By late afternoon that day, it had become too overcast for deep shadows, so I went back a couple afternoons later to capture what that scene would look like later on a sunny day. The image below was made at 6:52 pm. (Click on image to enlarge. Then click back arrow to return to this post.)
Tree shadows at 6:52 pm on 09/09/21. (Made with ZEISS 50 mm f/2 macro lens on Nikon D850 on RRS TFC-24L tripod with BH-40 ball head. f/11, 1/15 sec, ISO 64.)
Those seemingly innocuous trees to the west (right of the photo) were now casting long, separated shadows across the road. These shadows would obviously make it more difficult to show gouges, tire marks, or even paint marks on the pavement.
Time permitting (i.e., it’s not a rapid response), it’s worth checking out where the sun and any shadows would be before you set out to inspect a scene.
For many years, I’ve been using The Photographer’s Ephemeris (TPE) https://photoephemeris.com/en to determine where the sun is going to be in relation to any accident site. (It’s now a subscription service, and well worth the small cost.) It’s extremely valuable if you need to show whether the sun could have been in the eyes of any drivers or witnesses.
And as in this case, it’s also useful for determining when you have the best chance of getting clean site images with minimal shadows. Below are the three TPE screen captures that show what information you get.
The first shows where the sun was when the 10:21 am photo (top one above) was made. (Click on image to enlarge. Then click back arrow to return to this post.)
TPE 10:21 am on 09/04/21.
The line of the sun is shown as the narrow gold line coming in from the lower right toward the pin marking where my tripod had been set up. Note that while the photographs were made looking south, the TPE diagrams have north at the top. So the morning sun in the east will be from the left side in the photos and from the right side in the TPE diagrams. (Just FYI, the wider yellow line at the upper right was the sunrise angle while the wider orange line at the left was the sunset angle.)
This diagram showed that at 10:21 am on 09/04/21, the sun would have been coming in from the eastern side of the road through a thick area of trees, which is exactly what was shown in the top photograph.
At 2:45 pm on the same day, the sun was beyond the thick trees to the east, yet below the tree line to the west. This should result in a photograph with minimal shadows on the road, as the second photo above shows. (Click on image to enlarge. Then click back arrow to return to this post.)
TPE 2:45 pm on 09/04/21.
When I went back a couple days later at 6:52 pm, the TPE diagram showed that the sun would now be far enough west that it would come through the line of single trees to the west once the sun got low enough in the sky. Once again, that is precisely what the third photo above illustrates. (Click on image to enlarge. Then click back arrow to return to this post.)
TPE 6:52 pm on 09/09/21.
TPE gives both the azimuth and altitude of the sun. In this post, I’m only using the azimuth for direction, and applying a general knowledge of how high the sun will be from experience. For a question about whether the sun was in a driver’s eye, you’ll have to use both azimuth and altitude. That’s a future post.
TPE has many more sophisticated applications, including using AI to show where the sun or moon will be in a scene. It’s well worth getting and exploring all of its features. (I have no ties to TPE nor receive any compensation from them. It’s just a great tool I highly recommend.)
Takeaways:
-1- Before you photograph your wreck site, it’s often worth determining when the sun will cause the fewest or shortest shadows on your road.
-2- The Photographer’s Ephemeris is well worth using when you need to know where the sun will be at specific times on specific dates.
It is essential to keep truck tires properly inflated so they can carry the load, wear evenly, maximize fuel mileage, and maintain their integrity. Chronic overdeflection (overinflation, underinflation, or a combination) is a common cause or contributor to tire failures.
During pre-trip inspections, the Federal Motor Carrier Safety Regulations (49 CFR §396.13) requires the driver “be satisfied that the motor vehicle is in safe operating condition.” This includes the truck’s tires . As part of that pre-trip tire inspection, a driver is trained to look for low or flat tires. But there is no requirement that the driver check the air pressure with a gauge. In fact, while going through truck driving school before getting my CDL, we never once used an air pressure gauge during our pre-trip inspection lessons, daily routines, or exams.
It would be an onerous task to require a driver to check the air pressure of all eighteen tires on a typical tractor trailer before every trip. As an alternative to a gauge, some drivers use a “tire thumper” (usually a rubber mallet or some kind of a bat) to check their tires. If a tire is inflated, the thumper would bounce right off. Striking a tire with little or no air would have no bounce back, but would respond with a flat thud. While a thumper can’t determine if a tire is properly inflated, it can let you know if a tire is flat or near flat. [Click on image to enlarge, then click back arrow to return to this post.]
Only the bottom four of these will give you an accurate truck tire inflation pressure. (Made with ZEISS Milvus 50 mm f/2 Macro lens on Nikon D850 at f/16, 1/200 sec, ISO 64. Used one Profoto B1x studio strobe with silver umbrella with diffuser on each side.)
Back in 1998, I bought the Trucker’s Toothpick & Tire Tester at the top of the photo at a truck stop just for fun. (Both the name of the product and the company are rather whimsical.) It is a weighted metal stick with a hand grip on one end and a protective cover on the other. Along with various wooden bats, it is typical of tire thumpers sold commercially. While their benefits are minimal, at least thumpers prevent a driver from starting off on a trip with a flat tire.
The three stick gauges in the middle of the photo look similar, but their dual heads are at different angles. One of them is bound to fit when the metal valve stems of either the inner or outer tire of a dual pair are bent and otherwise inaccessible. They prevent you from bleeding air out of the tire as you try to get the gauge head to seat on the valve.
Stick gauges seem tricky to read until you understand how their scale works. I’ll describe that below.
The digital pressure gauge at the bottom is the easiest to read (and photograph, if you do that—I don’t).
Here’s how to read a truck tire stick gauge. Assume you’ve just checked the air pressure of a steer axle tire and got the reading below. [Click on image to enlarge, then click back arrow to return to this post.]
Scale on truck tire inflation pressure gauge. (Made with Nikon 105 mm Micro lens on Nikon D850 at f/16, 1/200 sec, ISO 64. Used one Profoto B1x studio strobe with silver umbrella with diffuser on each side.)
At first glance, the scale might not seem to make sense with the decimals between the longest hash marks. (Gauges typically start at 10 psi, not 0 psi; anything less than 10 psi is obviously flat.)
Zooming in might help make deciphering the scale more clear. (This photo has been rotated clockwise to be oriented as you would read the scale in use.) [Click on image to enlarge, then click back arrow to return to this post.]
Rotated close-up of scale on truck tire inflation pressure gauge.(Made with Nikon 105 mm Micro lens on Nikon D850 at f/16, 1/200 sec, ISO 64. Used one Profoto B1x studio strobe with silver umbrella with diffuser on each side.)
Let’s start with the 100 psi mark. (Note that on this gauge, the 100 psi hash mark happens to intersect the second zero.) The next short hash mark down represents 102 psi. One shorter hash mark down is 104 psi. Just below that, the longer hash mark near the center of the scale represents 105 psi. The next short hash mark at the right edge below that is 106 psi. Below that, the short hash mark is 108 psi. Next is the longer hash mark for 110 psi. Using this information, you can see the inflation pressure reading above was 118 psi.
To summarize, all the hash marks along the right edge of the scale are in 2 psi increments. Half way between the decimals, the longer hash marks near the center of the scale are in 5 psi increments.
Anywhere along the scale, anytime the end of the barrel is halfway between two consecutive short hash marks, the inflation pressure is 1 psi greater than the short hash mark above it.
Takeaways:
-1- While truck tires must be properly inflated, the Federal Motor Carrier Safety Regulations do not require truck drivers to check tire inflation pressures with a gauge during their pre-trip inspections.
-2- Tire thumpers can indicate if a tire is flat or almost flat, but cannot determine the inflation pressure.
-3- Different angles of dual head inflation pressure gauges can help access bent valve stems.
-4- If using a stick gauge, make sure you accurately read the scale.
Photographs of collision sites in most intersections, or in residential or commercial areas, will have recognizable elements that orient a viewer to that area. Conversely, many stretches of rural roads, interstates, or other limited-access highways have few, if any, distinctive features. While it will be assumed that your photos show the road where the wreck occurred, without visible landmarks, it may be difficult for viewers to relate to the area. Signs, bridges, guardrails, and other roadside objects can be helpful—but only if you include them in your photographs.
As an example, the top of a fireworks store is partially visible at the top of the image below, but it isn’t visible enough for a viewer to determine where this photograph was made. [Click on photograph to enlarge, then click on Back arrow to return to this post.]
Accident site with truck blocking sign. (Nikon D810 with ZEISS Milvus 50 mm f/2 macro lens.)
By the way, this photograph was made for two purposes. First, it showed the roadway in the direction the accident vehicles were coming from. Second, it showed an oncoming vehicle as it crested the hill (vertical curve) on the approach to the area of impact to give a sense of the sight distances involved.
While the fireworks store is a partial clue, the timing of the tractor trailer in the above photo obsured an exit sign, visible below, that would definitively place where the photo was made to someone generally familiar with the area. [Click on photograph to enlarge, then click on Back arrow to return to this post.]
Accident site with sign as reference. (Nikon D810 with ZEISS Milvus 50 mm f/2 macro lens.)
Unless you intend to depict the effect of obscuring an element at a site, which sometimes you may wish to do, it is worth making a habit of reviewing your images while you’re still in the field to ensure you haven’t accidentally masked an important feature you meant to show.
Five takeaways:
-1- You should make photographs of the approach to a wreck scene to establish where the vehicle or vehicles came from.
-2- If a hill, curve, tree line, building, etc., obscures the view of an approaching vehicle, in any direction, you may want to capture the view both without any vehicles and then with a vehicle just coming into view to assist in visualizing the visibility distance.
-3- Especially on a rural road or on a limited-access highway, photographs including signs or other roadside features can help a viewer relate to where the photo was made.
-4- You can time your photographs so that passing vehicles will or will not obstruct certain roadside features at an accident site, depending on what you are trying to illustrate in each photo.
-5- You should include unobstructed permanent roadside objects in at least one photograph so you won’t be embarrassed by failing to fully document a wreck site.
Fill Flash helps bring out details in the shadowed area of high-contrast subjects. This first photo of the left front of a truck tractor without flash doesn’t have much detail under the fender. [Click on image to enlarge, then click on back arrow to return.]
Left Front of Truck with No Flash (ZEISS Milvus 50 mm macro lens on Nikon D850 at f/10, 1/50 sec, ISO 64.)
To bring out some detail, a flash was added at a reduced power output for this second image. (It’s more noticeable in an enlarged image.) Fill flash isn’t intended to light the entire image frame, but only to lighten very dark areas. [Click on image to enlarge, then click on back arrow to return.]
Left Front of Truck with Medium Fill Flash (ZEISS Milvus 50 mm macro lens on Nikon D850 with Nikon SB-910 flash at f/10, 1/50 sec, ISO 64.)
While there was a little more detail in the suspension and frame, raising the flash power added even more light under the fender. Again, it’s best to enlarge the image to see the effect. [Click on image to enlarge, then click on back arrow to return.]
Left Front of Truck with More Fill Flash (ZEISS Milvus 50 mm macro lens on Nikon D850 with Nikon SB-910 flash at f/10, 1/50 sec, ISO 64.)
Note that all three photographs were made at the same exposure of f/10, 1/50 second, and ISO 64. The images differ because the amount of fill flash was different. This showed the flash was supplemental or “fill” meaning flash filled in the shadows without altering the overall exposure.
Before you make any photograph, look for areas that are too dark to show details you may want. By varying the power of the flash, you can bring out as much detail as you choose, without affecting the overall exposure.
Two takeaways:
-1- Fill flash adds light in the shadows without affecting the overall exposure, which stays the same.
-2- You can control the amount of shadow detail you want to show by changing the output of your flash, or its flash power.
Note: This is an updated and enhanced version of a post originally made in July 2018.
After having four of the five classes canceled last year, I’m really happy to announce the return of my SAE automotive and product photography class: https://www.sae.org/learn/content/c1729/. I’m glad to be returning to the site of my first class in 2018 at the great facilities of Mecanica Scientific Services in Oxnard, CA: https://www.mecanicacorp.com/. Many thanks to John Steiner, CEO and Principal Scientist of Mecanica, for hosting this upcoming class from August 30 through September 1, 2021.
Whether your primary job is accident reconstruction, product analysis, vehicle or component testing, or other technical area, you will need consistent, quality photographs to both document and analyze your subjects. These photos need to be made regardless of ambient lighting or conditions. Your camera on Auto isn’t going to do that. [Click on image to enlarge in new window, then click back arrow to return to post.]
Photo made by panning with vehicle moving at 55 mph during tire testing. (Made with Nikon 300 mm f/2.8 lens on Nikon D800E at f/6.3, 1/640 sec, ISO 400.)
Not only are good photos essential for documentation and useful for analysis, they can be critical for use in lawsuits, insurance claims, recalls, and design and testing evaluations. Both in-house analysts and independent consultants will be counted on to routinely produce accurate and reliable photographs as part of their professional work. Did I mention that your camera on Auto isn’t going to do that? [Click on image to enlarge in new window, then click back arrow to return to post.]
BMW in sun at tow yard. Fill flash and polarizer. (Nikon 24-70 mm f/2.8G lens on Nikon D810. Exposure: f/10, 1/60 sec, ISO 160.)
This class is designed to give you the tools and knowledge you’ll need to consistently create professional photographs by proper use of focus, depth of field, composition, lighting, polarizers, tripods, and close-up/macro tools. You’ll see how flash is essential for capturing all the data, and how it’s not as intimidating as many believe. We’ll also cover the two types of night photography as well. [Click on image to enlarge in new window, then click back arrow to return to post.]
Night photo of intersection with traffic light. (Made with ZEISS Milvus 50 mm f/2 macro lens on Nikon D850, at f/6.3, 1/60 second, ISO 1600.)
There will be more hands-on sessions than in previous classes, so make sure to bring your camera, lenses, polarizer, tripod, and flash. Course information and registration are available through the link in the first paragraph, but if you have any questions or need more information, please feel free to e-mail or call me directly.
In an earlier post, I showed how shooting a sponge with a side flash gave depth to its surface that couldn’t be shown using a direct flash. I used a sponge since sponges are small, readily available, and easy to practice with anywhere. In this post, I’ll show how a side flash gives depth to an automotive subject—namely, a tire tread.
For this first image, I didn’t use any flash, but adjusted the camera for a proper exposure for the ambient light. It’s properly exposed, but the depth and extent of the cuts and chips out of the tread aren’t apparent. (Click on photo to enlarge, then click on back arrow to return to this post.)
Perpendicular to tread with no flash. (Made with ZEISS Milvus 50 mm f/2 Macro lens on Nikon D850 at f/16, 4.0 sec, ISO 100.)
This photo was made in my Studio Lab, which has so many LED shop lights overhead people say it looks like an operating room. Even though the room looks bright to our eyes, there is not as much ambient light for photography as you might think. In fact, to make the image above required a 4.0 second shutter speed, which obviously precluded handholding the camera. (I also increased the ISO 2/3 stop from 64 to 100.)
For the second shot, I added a Profoto B1x flash to each side, almost perpendicular to the camera, shooting across the tread. I triggered them with a Nikon SB-910 flash in the hotshoe that was pointed straight up at a very low power so it would not contribute to the exposure. (Click on photo to enlarge, then click on back arrow to return to this post.)
Perpendicular to tread with one flash to each side. (Made with ZEISS Milvus 50 mm f/2 Macro lens on Nikon D850 at f/16, 1/200 sec, ISO 64. One Profoto B1x strobe to each side triggered by a Nikon SB-910 flash in the camera’s hot shoe.)
Side flash enhances texture by creating shadows. Diffused ambient light and direct flash lighting both evenly light your subject, which fills in the shadows, which, in turn, reduces the appearance of any textures.
[Technical aside #1: With cross-light from the added side flashes, the shutter speed was 9 2/3 stops faster at 1/200 second and the ISO was 2/3 stop less at 64, for a total of 10 1/3 stops less light than the first shot. If the flashes were turned off for the second photo, that exposure would have resulted in a pure black image. The flashes were adjusted to give the proper amount of light for the exposure. This is called a full flash image, where all of the light is provided by flash. This differs from a fill flash image where the light from any flash enhances the ambient exposure, but flash isn’t the only light source. More on this later.]
[Technical aside #2: For an equivalent ambient light image, instead of a 4.0 second shutter speed and ISO 100, you could use 1/60 second shutter speed and ISO 256,000. The 1/60 second shutter speed may allow you to handhold the camera, but ISO 256,000 is guaranteed to be extremely noisy and noticeably lacking in dynamic range. Not a good alternative at all.]
Four major takeaways:
-1- As with the earlier sponge example, flash light coming from the side brings out texture by creating shadows.
-2- Both diffused ambient light and direct flash lighting flood every surface with the same light, obscuring texture and depth differences.
-3- Indoor ambient light may look bright to our eyes, but it will require very long exposures or an extremely high (and noisy) ISO to make the photograph.
-4- You must adjust your exposure accordingly when going between ambient light and full flash lighted images.
Where you place your camera determines the relative positions of objects in your frame. It’s important to be aware of any unintended impressions by the juxtaposition of the objects you are showing. This is best avoided by making photographs from enough different angles to give a complete and accurate representation of the positions of all the elements.
The subject of these photographs was a disused flatbed semi-trailer. It was in a rural field with a number of other discarded vehicles . None could be moved.
All of these photographs were made with the same 50 mm lens on the same full frame sensor camera so there was no variation in the field of view between the images. As mentioned, neither the trailer nor the car were moved. My camera was on a tripod (as always) so all the photos were made from the same camera height.
In the first photo, how far under the trailer do you think the rear of the gold car was? Was its rear bumper against the left landing leg of the trailer? (Click on the image to enlarge, then click on the back arrow to return to the post.)
Juxtaposition of trailer and car #1. (Made using Nikon D850 with ZEISS Milvus 50 mm f/2 macro lens, Nikon SB-910 flash, and Really Right Stuff TVC-24L tripod. Exposure: f/14, 1/30 sec, ISO 64.)
Moving the camera to the right showed the car’s rear bumper was not against the landing leg, but can you estimate how far the trunk lid was under the side of the trailer? (Click on the image to enlarge, then click on the back arrow to return to the post.)
Juxtaposition of trailer and car #2. (Made using Nikon D850 with ZEISS Milvus 50 mm f/2 macro lens, Nikon SB-910 flash, and Really Right Stuff TVC-24L tripod. Exposure: f/14, 1/30 sec, ISO 64.)
Further right, looking directly at the front of the trailer, the car’s rear bumper was actually quite far from the trailer’s landing leg, and its trunk lid doesn’t look nearly as far under the trailer as in the two previous photos. (Click on the image to enlarge, then click on the back arrow to return to the post.)
Juxtaposition of trailer and car #3. (Made using Nikon D850 with ZEISS Milvus 50 mm f/2 macro lens, Nikon SB-910 flash, and Really Right Stuff TVC-24L tripod. Exposure: f/14, 1/30 sec, ISO 64.)
Moving even farther to the right, you can now see that none of the rear of the car was under the side of the trailer. Again, neither vehicle was moved during this sequence. (Click on the image to enlarge, then click on the back arrow to return to the post.)
Juxtaposition of trailer and car #4. (Made using Nikon D850 with ZEISS Milvus 50 mm f/2 macro lens, Nikon SB-910 flash, and Really Right Stuff TVC-24L tripod. Exposure: f/14, 1/30 sec, ISO 64.)
Three takeaways:
-1- Be aware of possible deception from a single photograph, both when making the photos yourself, and when evaluating photos provided to you. If the first image had been from a wreck scene, you certainly don’t want to opine that the rear of the car ended up under the trailer!
-2- Take multiple images from different camera positions to give a complete and accurate depiction of your subjects and their relationships to other objects in the frame.
-3- As mentioned in previous posts, using a tripod for every image not only insures a sharp image, but allows careful framing and a consistent look between images all made at the same height.
On Thursday, April 1, 2021 (and, no, it wasn’t an April Fools joke), I had the honor of being interviewed by Eugene Liscio of ai2-3D for his Forensics Talks YouTube channel.
Forensics Talks YouTube interview by Eugene Liscio
For almost an hour, we talked about a wide range of topics related to tire, vehicle, and accident reconstruction photography. Among the subjects we discussed were the importance and use of a tripod, a polarizer, and flash. We also touched on both kinds of night photography and on post-processing.
I hope you will find the information we discussed useful. The interview also gives an idea of a couple of the topics which we demonstrate and discuss in depth in my SAE class which, by the way, will be resuming as in-person classes this year.
Here’s a link to that class: SAE C1729. I’ll post the dates of the new classes as soon as we finalize them.
