SAE International’s Accident Recon Digital Summit 2024

On Tuesday, February 6, 2024, I will be presenting One Flash is Great; Two (or More) Can Be Better! at the third annual SAE International’s Accident Reconstruction Digital Summit 2024.

One flash will both balance the exposure and bring out details that would otherwise be hidden in shadows. A second (or third or…..) flash is sometimes essential to show textures or to reveal information hidden in remaining shadows. While some people fear using even one flash, you’ll see that it’s actually quite easy to use one or more flashes to add light where it’s needed, making your images even more useful. [Click on image to enlarge, then click on back arrow to return to this post.]

Tire and wheel inside semi-trailer. (Made using Nikon D850 with ZEISS Milvus 35 mm lens and on-camera Nikon SB-910 that also fired two Profoto B10s.)

The Summit is a free online event over two days. My presentation will be first out on Day One at 11:00 a.m. EST on Tuesday, February 6.

Both days will feature presentations on a variety of current topics that accident reconstructionists are facing now, and that will be even more prevalent in the future.

Registration is free at this link:  https://www.sae.org/attend/accident-reconstruction-digital-summit

Hope to see you there.

2024 Forensic Photography Symposium (FPS)

FPS 2024 Banner

From January 22 through 25, 2024, Eugene Liscio of ai2-3d Forensics (https://www.ai2-3d.com/) is hosting the third annual virtual International Forensic Photography Symposium (FPS 2024). It features an incredible variety of relevant, useful forensic photography topics from a diverse group experts in their fields.

In addition to the presentations, new this year will be several workshops in the morning sessions. Eugene asked me to conduct the first workshop on Photoshop techniques for forensic photography on Tuesday, January 23, 2024, from 10:00a to 12:00p (EST).

My workshop will include demonstrations of chromatic aberration correction, focus stacking, creating panoramas, and median stacking. We will also see how to bring out elements of the subject that are faint or may have faded over time.

We will then learn techniques for extracting additional details from your own or from supplied images from other sources. To wrap up, we will both apply these techniques to modifying images for exhibits, publications, or teaching, and see examples of improper manipulations.

Importantly, throughout the workshop, we’ll make sure that every step in every image will be preserved, can be reversed, and can be replicated by anyone else, without a single permanent, irrevocable adjustment being made.

All FPS presentations and workshops will be recorded and available to all registrants after the symposium. I’ve found this quite useful to review new, detailed, or complex ideas from presentations. This will be especially important for my workshop since we’ll be using a lot of techniques but won’t have the time to describe each one in great detail. With the videos, you’ll be able to try the techniques on your own images later.

All four days of presentations and workshops—along with the post-symposium videos—are offered for the incredibly low price of US$150 (US$75 for full time students).

Here is a link to the schedule and registration: https://www.ai2-3d.com/schedule-fps2024.

 

Focus Stacking Close-up Images

The closer you get to your subject, the less depth of field (DOF) you have. As you can imagine, when you photograph close-up or macro or micro subjects, you get progressively even less DOF.

In close-up—or closer—shots, even stopping down to your smallest aperture won’t give you enough DOF to make much of a difference. Besides, if you fully stop down your aperture, any small gain in DOF will likely be negated by diffraction, which softens the entire image.

Focus stacking blends multiple images with increasingly further focus points into a single image. This allows you to create an image with the specific DOF you want for your subject . You might not need everything in the foreground or background sharp, but you control what is or isn’t in focus by how many images (called slices) you use.

For this example, I wanted the entire broken lug stud in focus, but wasn’t concerned about the hub surrounding it. As shown below, even stopping down to f/16 didn’t give sufficient DOF to show the entire fracture surface. [Click on image to enlarge, then click on back arrow to return to this post.]

Single image at f/16 made with Nikon Z 8 with Nikon Z 50 mm MC macro lens. One Profoto B1x studio strobe on either side with Godox T365N II flash mid-left. f/16, 1/200 sec, ISO 64.

Notice how the focus quickly falls off toward the farther end of the broken lug stud fracture surface. Both the foreground and background of the hub are out of focus, but that’s okay since they’re not the subject of the photograph.

To get the entire lug stud to be in focus, I made nine separate photographs of the fracture surface with each one focused slightly further from the camera. [Click on image to enlarge, then click on back arrow to return to this post.]

Each individual image from closest focus upper left to farthest focus lower right, each made with Nikon Z 8 with Nikon Z 50 mm MC macro lens. One Profoto B1x studio strobe on either side with Godox T365N II flash mid-left. Each component image f/16, 1/200 sec, ISO 64.

In Photoshop, I brought all of the raw frames (slices) into a single image as separate layers. I aligned the layers, then stacked them using Auto-Blend Layers. As shown below, using layer masks, this function blocked the out of focus areas on each slice. Only the sharpest parts of each layer, or slice, remained. [Click on image to enlarge, then click on back arrow to return to this post.]

Screenshot of Photoshop layers with their focus stacking masks.

I cropped the image back to its original size and saved it with all its layers as a PSB Photoshop Big) file. With ten 45 megapixel layers, the file was over 2 GB, which is larger than can be saved as a PSD (Photoshop Document) file. I then flattened the image, resized it, output sharpened it, and saved it as JPEG. Note: I still always keep the PSB file with the layers and layer masks to be able to show what I did, if asked.

Below is the result of the focus stack blending of the nine layers shown above. [Click on image to enlarge, then click on back arrow to return to this post.]

Focus stacked in Photoshop from nine images, each made with Nikon Z 8 with Nikon Z 50 mm MC macro lens. One Profoto B1x studio strobe on either side with Godox T365N II flash mid-left. Each component image f/16, 1/200 sec, ISO 64.

Note how the entire face of the fracture surface is now in focus. Note: I used to also use Zerene Stacker and Helicon Focus for focus stacking—and both are excellent—but now I almost exclusively use Photoshop.

Takeaways:

-1- The closer your camera is to your subject, the less depth of field (DOF) you will have.

-2- Most forensic images require the entire subject to be in focus to show all its details.

-3- Even stopping your lens down to its minimum aperture won’t give you sufficient DOF, plus you risk losing detail from diffraction.

-4- Focus stacking requires a series of photographs (slices) be made with the focus increasingly distant from the camera. These slices are blended into a single image where only the sharpest elements of each slice will be kept by the software.

-5- Only combining images through focus stacking allows you to get sufficient DOF for many close-up, macro, and micro images.

-6- The closer the subject, the more slices (individual images) you need. For some micro images, more than 1,000 slices need to be blended through focus stacking.

-7- Focus stacking can also be used for large subjects including landscapes, buildings, accident scenes, and vehicles. Those larger subjects require fewer slices—often only two or three.

Why Full Auto Exposure Mode Creates Inaccurate Night Photographs

One kind of forensic night photography requires you to accurately capture the appearance of a scene as closely as possible under lighting conditions similar to what they were at the time of an incident. Of course that results in an overall image that appears dark since, after all, it is a night scene.

Using fully automatic exposure modes will result in the scene being significantly (and obviously) overexposed. This is because the camera is trying to record the scene as a mid-tone (frequently referred to as “middle gray” even when the subject isn’t gray). This automatic brightening of night scenes usually results in noisy, overexposed images that don’t resemble the actual scene at all.

Almost all consumer and prosumer cameras have a fully automatic exposure mode denoted by a green camera icon with or without the word “Auto”. The image below shows the full Auto mode icon on a Nikon D5600 and Canon T7i. (Professional cameras like my Nikon Z 8’s often do not have this mode.) [Click on the image to enlarge. Then click on back arrow to return to this post.]

Made with Nikon D850 and ZEISS Milvus 100 mm macro lens.

In Auto mode, the camera sets the aperture, shutter speed, and ISO, and you cannot change or override any of them! Because the photographer cannot affect exposure in any way in full Auto mode, when teaching I refer to it as the “Green Mode of Shame” to drive home the point that you as the photographer are left without any ability to control your exposure (or a number of other important settings). While this mode might work for ideal lighting during the day, it just doesn’t—and can’t—work for ambient light night photographs. (Note: Semi-automatic exposure modes Program, Aperture Priority, and Shutter Priority will be addressed in a future post.)

I made the following two images in a lighted parking lot that had a white, a black, and a silver vehicle in the scene. (Note: both images were captured in the camera’s raw NEF format.)

For this first image, I used a Nikon Z 5 in Auto mode (its Green Mode of Shame). As discussed above, the camera tried to create a mid-tone image, and I couldn’t do anything about it. [Click on the image to enlarge. Then click on back arrow to return to this post.]

Auto exposure mode with Auto ISO. Made with Nikon Z 5 with Nikkor Z 24-70 mm f/4 lens at 49 mm in raw mode. f/4, 1/50 sec, ISO 25,600.

Note the camera chose a wide open aperture to let in as much light as possible (f4 on that lens), and an ISO of 25,600(!), while setting the shutter speed to 1/50 of a second. (A shutter speed of 1/50 of a second is considered handholdable with a near 50 mm focal length. The thinking is that if someone is going to use a camera in Auto mode, the camera will most likely be handheld. Consequently, the camera will open the aperture and boost the ISO to keep the shutter speed handholdable. But as usual, I had this camera on a tripod, like I almost always do in any light. )

Even though the original image is quite noisy (the great reduction in size and the JPEG compression of this posted image reduced the appearance of noise from the original raw), that’s not the biggest issue with it. The real problem is the scene was nowhere near this bright; it didn’t look anything like this at the time I made this image.

For the image below, I switched to manual exposure mode (the only exposure mode I ever use). I kept the aperture at f/4, but then set the ISO to the camera’s minimum of 100 to minimize the image noise. Because the camera was on a tripod, I wasn’t too concerned about shutter speed as long as it stayed within reason. [Click on the image to enlarge. Then click on back arrow to return to this post.]

Manual exposure mode with ISO set at 100. Made with Nikon Z 5 with Nikkor Z 24-70 mm f/4 lens at 49 mm in raw mode. f/4, 1/3 sec, ISO 100.

With the aperture and ISO set, I adjusted the shutter speed until the image on the back of the LCD looked like what I was seeing with my naked eye. As it turns out, the Auto image was four stops lighter than this more accurate one.

Note 1: By default, I have the camera’s Picture Control set to Neutral with reduced contrast and saturation so the LCD closely matches my computer monitor.

Note 2: For an actual night photograph case, I start by tethering my camera to a laptop that is calibrated to match my desktop monitor. There’s much more to the actual process than I did for this demo, but it’s close enough to illustrate the point that you need to take manual control of the camera.

While this second image is close to showing the scene as I saw it, to view it properly, you would need to view it with a black surround in a darkened room with your monitor brightness set to 140 cd/m² to match what I see. Regardless of these technicalities, comparing the two images—in whatever light you’re in or computer you’re on—it is obvious that the upper Auto exposure image doesn’t look anything like the more accurate lower manual exposure mode image.

In a number of cases where I’ve done both the night photography and explained why photographs submitted by other experts or photographers were improper and misleading, all of those inaccurate photographs have been stricken and disallowed by the judge.

While it’s a little bit off-topic, being able to explain how and why photographs were made and why they accurately represent what they purport to show—and why other ones don’t—is critical in almost all ambient light night photography cases.

Takeaways:

-1- Fully automatic exposure modes (like Auto) are not designed to—and cannot—accurately capture ambient light night images.

-2- You need to shoot night photographs using manual exposure mode with a low ISO to minimize noise, with the appropriate aperture for the depth of field you need, and with the shutter speed set to match what the scene looks like to the naked eye. There’s much more to the whole process, but that’s the essence of it.

-3- While the lower photo looks much closer to what the parking lot looked like when I made the photographs, it was not made with the procedure I use for case work. It is close enough to make a quick demo comparison against a demonstrably incorrect Auto method that yielded a demonstrably incorrect image.

Using Two Flashes in Full Sun

This tire was photographed in the afternoon on a sunny day. [Click on the image to enlarge. Then click on back arrow to return to this post.]

Mounted tire on wheel outdoors with no flash. (Made with Nikon Z 8 and ZEISS Milvus 50 mm macro on Nikon FTZ II adapter at f/16, 1/10 sec, ISO 64.)

Despite being properly exposed, there are almost no details in the shadows of the tire sidewall or the wheel. Brightening the exposure would have shifted the brightest parts of both the wheel and tire into blown out highlights and all detail there would have been permanently lost. While not essential to the tire or wheel, the brighter spots on the concrete driveway would also have blown out. This would result in a less professional looking image.

Fortunately, the overall exposure itself can remain, and flashes can be used to bring out details in the shadows. [Click on the image to enlarge. Then click on back arrow to return to this post.]

Mounted tire on wheel outdoors with both on-camera flash and second flash at lower right. (Made with Nikon Z 8 and ZEISS Milvus 50 mm macro on Nikon FTZ II adapter. Godox TT685N II in camera hot shoe and Godox AD200 Pro at lower right at f/16, 1/10 sec, ISO 64.)

While keeping the identical exposure, a Godox TT685N II speedlight was slid into the camera’s hot shoe and aimed towards the shadows inside the wheel and on the left side of the tire sidewall. A second Godox flash—an AD200 Pro—was handheld at the lower right, and angled upwards toward the right side where the tread used to be.

These two flashes balanced the natural light and added much-needed detail in the shadows. The result was both a professional appearing image and one where details were not blocked up in dark shadows or blown out in the highlights.

Of course, like almost every photograph I make, both of these images were made with the camera on a tripod. I used a five-second self-timer so I could move over and get the handheld flash at the lower right into position.

Takeaways:

-1- On bright sunny days, there is often too much contrast to capture detail in both the highlights and the shadows.

-2- Increasing the exposure will lighten the shadows, but will cause the highlights to blow out and permanently lose all data and detail there.

-3- Adding one or more flashes to fill in shadows where needed results in more detail in the shadows without losing detail in the highlights.

-4- You may have to make a couple different images with the flashes to get the proper amount of light and the proper angle of light for what you want. When I make more than one image, I only keep the one that shows the details I intended. If you feel you must keep all the images you make, no problem. Only use the best one in reports or as an exhibit.

-5- More good news! The more often you practice with one or more flashes, the more quickly and intuitively you will be able to get both the amount and direction of light that you want.

SAE Photography Class December 5-7, 2023, in Irvine, CA

I will be teaching Photography for Accident Reconstruction, Product Liability, and Testing – C1729 in Irvine, CA, on December 5-7, 2023. Please check out this link for more information or to register:  https://www.sae.org/learn/content/c1729/.

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.)

[Click on photo to enlarge, then click on back arrow to return to this post.]

In addition to the class presentations and materials, I will be bringing various tripods, tripod heads, and accessories, along with a lot of Godox flashes that we’ll use to practice multi-flash and off-camera flash techniques.

Please contact me if you have any questions about the class.

New SAE Photography Class Scheduled October 17-19, 2023!

SAE International has just added another of my photography classes (Photography for Accident Reconstruction, Product Liability, and Testing – C1729) at their excellent training center in Troy, MI, for October 17-19, 2023. Please check out this link for more information or to register:  https://www.sae.org/learn/content/c1729/.

Melted aluminum on lug stud. (Nikon D850 with ZEISS Milvus 100 mm f/2 macro lens.)

[Click on photo to enlarge, then click on back arrow to return to this post.]

In addition to the class presentations and materials, I will be bringing various tripods, tripod heads, and accessories, along with a lot of Godox flashes that we’ll use to practice multi-flash and off-camera flash techniques.

Mid-October is still a great time to be in Troy, with daytime highs about 60° and lows about 42°.  The SAE Troy facility is just off I-75 at W Big Beaver and is surrounded by hotels and restaurants, so is quite convenient.

Please contact me if you have any questions at all.

Truck Tire Revs/Mile in HVEDR Downloads

When inspecting a truck and downloading its HVEDR, it is important to document the actual tire parameters. This includes not only confirming tires sizes, but their load ranges. You must confirm that the tire sizes and load ranges match those on the safety certification label on the door jamb and in the values programmed into the HVEDR.

In its 2023 Truck Tire Data Book, Michelin summarizes the effects of different revs/mile in this Rule of Thumb: “When going from a lower Tire Revs./Mile [sic] to a higher Tire Revs./Mile, the actual vehicle speed is less than the speedometer reading. When going from a higher Tire Revs./Mile to a lower Tire Revs./Mile, the actual vehicle speed is greater than the speedometer reading.”

The revs/mile differences between load ranges in a given tire size might not be large, but they do exist—even in the same line of tires. For example, Michelin lists two 11R22.5 X Multi D tires: one load range G and the other load range H. For the load range G tire, Michelin lists the revs/mile as 496 while it lists 494 revs/mile for the load range H tire. Likewise, for the 11R22.5 Michelin X Line Energy Z tire line, the load range G revs/mile was 502 and the load range H was 503.

So just between two Michelin tire lines, there is a range of revs/mile from 494 to 503 for 11R22.5 tires. Not only that, but for one tire line, revs/mile were higher for the LRH tire than the LRG, while for the other tire line, the opposite was true.

At first it may seem that all tires of the same size would have the same revs/mile. But variations in tire construction, tread design, and tread depth can result in small variations in the actual revs/mile of a specific tire of the same size.

Tire companies determine the revs/mile from the test procedures set out in SAE Recommended Practice J1025. J1025 specifies speed (45 mph), load, inflation pressure, ambient temperature, configuration, break-in, warm up, surfaces, measurement devices, and test distances required for each test.

The four revs/mile values of the four 11R22.5 Michelin tires above weren’t far apart, but it is best to check and confirm. And even though a small difference in revs/mile may not end up being significant in your analysis, you want to confirm that the truck tires sizes and load ranges matched what was used when programming the HVEDR.

Many trucks have a variety of tire brands, sizes, load ranges, or a mixture of original and retreaded tires. In some cases, the truck may be gone or repaired, and all you have to work with is the HVEDR report itself. When you have tire variations or unknown tires, you might consider researching the ranges of any relevant tire property, like revs/mile, then running a sensitivity analysis to quantify the effect that range of values might have on any subsequent analysis involving data from the report.

Takeaways:

-1- During a truck inspection, don’t just document the tire manufacturer(s) and tire size(s), but be sure to include the tire load range(s). Compare their properties with the programmed values in the HVEDR report.

-2- If there are variations in the truck’s tires, check the various tire properties against the HVEDR programmed values.

-3- Using those tire property variations, it might be useful to perform a sensitivity analysis to quantify the effect of a range of revs/mile or other variable.

-4- To learn how to apply HVEDR data, I highly recommend SAE International class C1901 Advanced Applications of Heavy Vehicle EDR Data taught by Wes Grimes, Greg Wilcoxson, Dave Plant, and Brad Higgins:  https://www.sae.org/learn/content/c1901/

SAE Automotive Forensic Photography Class – April 2023

SAE International has scheduled my next Photography for Accident Reconstruction, Product Liability, and Testing (C1729) class at their excellent Troy, MI facility from April 4-6, 2023: https://www.sae.org/learn/content/c1729/

It’s a great facility and is quite easy to access on W Big Beaver Rd just off I-75. It’s about 45 minutes from the Detroit airport. There are plenty of hotels and a lot of great restaurants in every price range.

The link above provides a detailed course outline. We’ll also get hands-on time to practice with exposure, flash, polarizers, tripod use, and more.

If you have any questions or would like more details, please feel free to email or call.

I look forward to seeing you there!

Photographing into the Abyss with the Laowa Probe Lens

Well, maybe not the abyss, but into a recess….

I needed to document the bolt holes on a wheel that came off the front of a pickup to show whether or not the wheel had been loose on its studs.

After making overall photos of the wheel and tire assembly, I made close-ups of the mounting surface and bolt holes from the back of the wheel. But on the outside of the wheel, the bolt holes were too deeply recessed to use a standard macro lens.

It was important to photograph the lug nut mating surface at the bottom of each recess, but it was nearly impossible both to get light down each recess and to fill the image frame with each hole. I wanted to get sharp, detailed, full frame images of the mating surface—not images cropped from a larger view.

The solution was the unique Laowa Probe lens. (I have previously discussed another unique Laowa super macro lens. I’ve found Laowa lenses to be well made and optically excellent.)

As the photo below shows, the Probe is a 16-inch long tube with a small diameter 24 mm lens surrounded by tiny LED lights at its end. You use a small USB power brick to power those LED lights. Laowa supplies a USB cable with a built-in dimmer switch, but you must supply the power brick. [Click on photo to enlarge, then click on back arrow to return to this post.]

Nikon D850 with Laowa 24mm f/14 2X Macro Probe macro lens made with Nikon Z 7II with Nikon Z 24-70 mm f/2.8 lens and two Profoto B1x studio flashes. f/16, 1/200 sec, ISO 200.

Laowa offers the Probe with several different mounts for many popular DSLR and mirrorless cameras. I used the Nikon F-mount version of the Probe lens on my Nikon D850. Note that all versions of the Probe require manual focusing and exposure; there are no electronic connections between the Probe and any camera.

Fortunately, the lens barrel fit perfectly into the recessed bolt hole, allowing me to get a full frame image of the mounting surface at the bottom. All I had to do was to adjust the intensity of the LEDs, adjust the exposure, and click the shutter. [Click on photo to enlarge, then click on back arrow to return to this post.]

Nikon D850 with Laowa 24mm f/14 2X Macro Probe macro lens made with Nikon Z 7II with Nikon Z 24-70 mm f/2.8 lens and two Profoto B1x studio flashes. f/16, 1/200 sec, ISO 200.

To steady the lens, manually focus, and keep the lens perpendicular to the bottom of the recess, I had the camera mounted on my rolling studio camera stand, which acted like an easily-adjusted tripod on wheels.

As you’ll see, the next two images made with the Probe lens required 0.5 and 0.3 second exposure times, respectively. That range of shutter speeds required that the camera  be secured on a tripod to eliminate camera shake. Raising ISO to get handholdable shutter speeds would introduce noise, reduce detail, and reduce dynamic range. That would defeat the whole purpose of using the Probe to get sharp, detailed full frame images.

The first image I made for each paired hole (the wheel was drilled for two bolt patterns) was to show the bolt hole pair, while concentrating on the appropriate bolt hole. [Click on photo to enlarge, then click on back arrow to return to this post.]

Nikon D850 with Laowa 24mm f/14 2X Macro Probe. f/unrecorded, 0.5 sec, ISO 64.

I then slid the end of the Probe deeper into the recess to fill the frame with details of the mounting surface. [Click on photo to enlarge, then click on back arrow to return to this post.]

Nikon D850 with Laowa 24mm f/14 2X Macro Probe. f/unrecorded, 0.3 sec, ISO 64.

I know of no other way to have attained this image without significant cropping and the inherent loss of detail and resolution.

Although it’s not a lens I use all that often, I’ve found the Probe unmatched for photographing inaccessible labels, fasteners, or other components, too. The built-in LED lights around the lens make it a really useful tool.

If you have (or anticipate) a singular need for it, you can rent one in just a day or two from someone like LensRentals.com at: https://www.lensrentals.com/catalog_search?q=laowa+probe.

Takeaways:

-1- The Laowa Probe (along with the more recent Peri-Probe) lens is a unique, specialized macro lens that can allow you to photograph areas that are otherwise inaccessible.

-2- The Laowa Probe lens allows you to capture all the resolution and detail of full frame images that would be lost with a significant crop.

-3- If you are stymied about how to photograph a challenging subject, you might be able to find a commercially available specialized solution.

-4- While it is preferable to have specialized lenses at your disposal, you can always rent lenses (or other photography gear) for infrequently encountered situations. Of course, you might find yourself using even seemingly specialized lenses more often if you own them and have them readily available.