Why are Full Frame DSLRs called 35mm Equivalents?

Digital single-lens reflex (DSLR) cameras have either full-frame or cropped sensors. A full-frame DSLR sensor (called FX by Nikon) yields an image size approximately 24 mm x 36 mm, just like 35mm SLR film cameras did. Crop sensor cameras are usually 1.5x (DX for Nikon) or 1.6x (APS-C for Canon), but can be 1.2x or 1.3x.

If the full-frame image size is 24 mm x 36 mm, why is it called 35mm? It’s obviously not the length of either side. The diagonal is 43.3 mm, so it’s not that either. (Click on image to enlarge, then click back arrow to return.)

35mm film width. (Made with ZEISS 50mm f/2 macro lens on Nikon D850.)
As the photograph shows, it turns out that 35 mm refers to the width of the film strip, including the sprocket holes.

While the “35 mm” designation has no direct relevance to the digital sensor size, it is still useful when referring to the focal length of lens. The diagonal, horizontal, and vertical angles of view of a given lens are the same with a full-frame digital sensor as they are on a 35 mm film camera. For example, the ZEISS Milvus 50 mm f/2 macro lens has a horizontal angle of view of 38 degrees on a full-frame digital sensor just as it does on a 35 mm film camera. The cropped sensor equivalent values will be the subject of another post.

Suggested Gear for Accident Reconstruction, Product Liability, and Testing Photography

Even before I started teaching Accident Reconstruction, Product Liability, and Testing Photography classes, I’ve often been asked about what photo gear works the best for those areas.

In response, I’ve created two wish lists at B&H Photo Video: one for Nikon Nikon Gear Wish List and one for Canon shooters Canon Gear Wish List. I’m a Nikon shooter, so most of my direct experience is with Nikon equipment. Here are some notes on the lists:

-1- I currently use the Nikon D850. It’s arguably the best all-around camera on the market, but I recommend the Nikon D750 for Nikon shooters for several reasons:
– Its files are more manageable in size, but are still plenty large.
– It still has the manageable body size and shape, and even has the really useful flip up and down LCD screen.
– It has a built-in flash to use to trigger the Nikon 4804 R1 macro flashes.
– The built-in flash isn’t terribly powerful, and can’t be rotated or removed, but can be used in a pinch.
– Right now, it is on a fantastic sale—especially with the 24-120 mm lens. You save $1,200 instantly.
– It’s been out for a while, and is tried and true.

There are similar advantages for Canon shooters with the 6D Mk II vs. the 5D Mk IV. If you have the budget, the Nikon D850 or Canon 5D Mk IV can’t be recommended highly enough. But they are not necessary for the work we do.

-2- The lists show both the ZEISS Milvus 50 mm and either Nikon 60 mm or Canon 100 mm macro lenses. I use the ZEISS, but also have the Nikon. I use my ZEISS Milvus 50 mm lens for most of my work photography, since it has a normal perspective. I also use the ZEISS Milvus 100 mm lens when I need to fill the frame with a macro shot, but can’t get close enough.
Advantages of the ZEISS are: Precise manual focus; amazing micro contrast; and, 50 mm is accepted “normal” lens that I use for almost everything.
Disadvantages of the ZEISS are: Manual focus only (but that is my preference); and, only enlarges to 1:2 (or half life-size).
Advantages of the Nikon: 1:1 (life-size macro); autofocus (but see note below); close enough to “normal” focal length; and, less expensive.
Disadvantages of Nikon: Not as easy to manually focus.
Note: When shooting macro images, you’ll most likely have to manually focus anyway, so having a more precise manual focusing ring is a real benefit.

Speaking of ZEISS lenses, four ZEISS manual focus prime lenses make up my work kit: the classic ZEISS 25 mm f/2 Distagon; the ZEISS Milvus 35 mm f/2; the ZEISS Milvus 100 mm f/2 macro; and, the aforementioned ZEISS Milvus 50 mm f/2 macro. I use the latter for 90 percent of my work. ZEISS makes lenses for Nikon, Canon, and Sony mounts. They have unrivaled sharpness and micro-contrast, and such smooth and accurate manual focusing that you’ll forget autofocus exists! Continue reading “Suggested Gear for Accident Reconstruction, Product Liability, and Testing Photography”

Adding Light with a Reflector

Even once you get your flashes dialed in to give you the exposure you want, there may be areas where you need more detail in the shadows. You can add lights, or just use a reflector. For this example, the flash lighting illuminated the tire just as I wanted, but the tread area in the foreground was too dark. (Click on image to enlarge, then click on back arrow to return.)

Sidewall lit with studio flashes, but tread in shadow. (ZEISS Miluvs 50mm f/2 macro lens on Nikon D850.)
I could have added one or more lights to illuminate the tread, but I chose to place a simpler silver reflector at an angle next to the shadowed tread. This allowed me to redirect the spill light from the flashes back into the tire’s tread.
Sidewall lit with studio flashes, with silver reflector lighting the tread. (ZEISS Miluvs 50mm f/2 macro lens on Nikon D850.)
I used the silver side of a Profoto collapsible white/silver reflector to bounce light into the shadows. The beauty of a reflector is that it does not affect the overall exposure, so there was no need to re-meter to determine the proper exposure.

Eliminate Traffic with Neutral Density (ND) Filters

It is often difficult to photograph highways without traffic blocking part of your shot. But you can effectively eliminate moving vehicles from your photo by using a dark neutral density (ND) filter. Neutral density filters are neutral gray gel or glass filters that require longer shutter speeds for the same exposure with the same aperture and ISO, depending on how light or dark the filter is.

This first image was made on a mostly sunny day without any filter over the lens. The vehicles are all slightly blurred, but are still recognizable. (Click on image to enlarge, then click on back arrow to return.)

Traffic barely blurred with no ND filter. (ZEISS Otus 85 mm f/1.4 lens on Nikon D850.)
At my Nikon D850’s lowest numbered ISO of 64, I chose an aperture of f/9 on my ZEISS Otus 85 mm lens. This yielded a shutter speed of 1/125 second. If the vehicles were traveling at the 65 mph speed limit, they would have traveled 0.76 feet during that 1/125 second. That small movement explains the minimal blur of the vehicles.

To blur the vehicles by increasing the shutter speed, I screwed a 3-stop Formatt Hitech Firecrest Ultra ND filter onto the front of the lens. Keeping the f/9 aperture and ISO 64 settings with the same lens, this reduced the shutter speed to 1/13 second (which was actually 3 1/3 stops less).

Traffic blurred with 3-Stop ND filter. (ZEISS Otus 85 mm f/1.4 lens on Nikon D850.)
At 1/13 second, vehicles at 65 mph would travel 7.3 feet. This rendered the vehicles as no longer recognizable, but they still blocked sections of the roadway.

For this final image, I replaced the 3-stop ND filter with a 10-stop Formatt Hitech Firecrest Ultra ND filter. I again kept the aperture at f/9 and the ISO at 64 while using the same ZEISS Otus 85 mm lens. This yielded a shutter speed of 2.5 seconds, which was 8 1/3 stops slower. (Note: the edge of a cloud resulted in a slightly underexposed image, so I increased the exposure by one stop in post-processing, so this final image was 9 1/3 stops less than the original without the filter.)

Traffic gone with 10-Stop ND filter. (ZEISS Otus 85 mm f/1.4 lens on Nikon D850.)
At the 65 mph speed limit, vehicles covered 238.3 feet in 2.5 seconds. Assuming the dashed lane lines plus spaces were at the standard 40-foot increments, the length of the roadway shown in any lane in this photo was much less than 238.3 feet. Consequently, every vehicle in both directions crossed the image frame in a fraction of the time the shutter was open. This meant vehicles would never register, but would leave only faint blurs across the image.

Here are some factors to consider:

-1- This only works when traffic moves fast enough not to register while the shutter is open. It won’t work at all in slow or stopped traffic, since slow or no movement would allow the vehicles to register in the frame, even at longer shutter speeds.

-2- Bright sunshine complicates the problem since your shutter speed will be quite high because of bright ambient light. The amount of ND needed will depend on the ambient light levels and the speed of the traffic.

-3- Dark ND filters will likely fool your Auto White Balance (WB) like it did for the 10-stop filter. I corrected it with one click in Adobe Camera Raw. This wouldn’t have been the case had I initially set the WB to a specific value.

-4- If I had exposed the darkest for another stop (that is, 5 seconds instead of 2.5 seconds), I would not have had to brighten it by a stop in post, and there would have been even less chance of a blurred streak from passing vehicles. When in doubt, it is always better to slightly overexpose (as long as you’re not blowing out your highlights) to get the slowest shutter speed possible for the least perceptible blurred streaks.

-5- You can stack multiple ND filters to get the amount of neutral density you desire. Variable ND filters allow you to rotate part of the filter to darken or lighten the effect of the filter.

-6- The numerical value of an ND filter is unimportant. You just need one dark enough to get your shutter speed slow enough to reduce the vehicles to imperceptible blurs.

-7- I always work with a tripod, but even if you don’t, a tripod is absolutely necessary for the long exposure images. There is no way to handhold a camera steady for 1/13, much less 2.5, seconds.

Photographing Testing Personnel

While working so intensely together to conduct testing for publication, it is worth taking the time to make photographs of all those who participated. The photos can be useful for a report, any paper presentations, and the websites of the participants. (Click on image below to enlarge, then click on back arrow to return.)

Three testing partners with tractor trailer (ZEISS 50 mm f/2 macro lens on Nikon D810.)
From left to right are truck and truck ECM guru Greg Wilcoxson (Wilcoxson Consulting, LLC), truck, data acquisition, and, well, everything else guru Wes Grimes (Wes Grimes, Collision Engineering Associates), and me. In an earlier post, you’ll find a link to the papers we wrote together from this testing.

Even with my hat, I was hardly in their league. We did have fun in the evenings when I would walk into a restaurant first, and tell the hostess or host that I was their bodyguard, and needed to get them a good table. We should have recorded their reactions.

A photograph of something as long as a tractor trailer is often best presented in a panoramic format (much wider than tall). This focuses attention on the subject by eliminating excessive sky and foreground.

Benefits of Fill Flash

While may seem counterintuitive, adding fill flash even on a bright, sunny day brings out details that better document your subject, which can make your photos even more useful. In this first image, the car and measurement rod were properly exposed, but the high contrast from bright sun resulted in little detail in the deep, dark shadows. (Click to enlarge image, then back arrow to return.)

High contrast from bright sun with no fill flash. (ZEISS Milvus 50 mm Macro lens on Nikon D850.)
Adding light from a flash resulted in a more balanced image, with details now visible even in components on the frame, suspension, and under the hood. The car and measuring rod remain properly exposed.
Excessive contrast reduced with fill flash. (ZEISS Milvus 50 mm Macro lens on Nikon D850 with Nikon SB-910 flash.)
Determining the amount of fill flash needed will be a topic for future posts. In the meantime, it’s worth experimenting with both manual and TTL flash settings until it becomes second nature.

Focus on Your Subject

Especially when handholding a camera, autofocus points might land on an object closer or farther away from your intended subject. This can result in an unimportant element in sharp focus, while your subject isn’t sharp.

There are three main ways to avoid this:
-1- Use manual focus. This allows you to choose what will be sharpest in your image, even if you recompose or your camera moves, as long as you remain the same distance from your subject.
-2- Put camera on a tripod, then move your autofocusing point until it’s on your intended subject.
-3- If handholding, autofocus on your intended subject, press your focus lock button, and recompose.

Your intended subject should be in focus. For this pair of photographs, the camera was on a tripod. In this first image, the autofocus point latched onto the black cable shield in the foreground. This caused the axle and wrapped tire behind it to be soft. (Click on image to enlarge, then back arrow to return.)

Focus on black cable wrap in foreground, not on axle or wrapped tire. (Nikon 24-70 mm f/2.8E lens at 50 mm on Nikon D850.)
For this second image, the focus point was moved off the cable wrap and onto the axle and wrapped tire.
Focus on axle and wrapped tire, not black cable wrap in foreground. (Nikon 24-70 mm f/2.8E lens at 50 mm on Nikon D850.)
Which photograph is correct? Depends on whether the subject is the black cable wrap or the tire and axle. Make sure you focus where you intend.

Watch What You Focus On

If you use autofocus lenses, make sure the focus point is where you want it. I almost exclusively use ZEISS manual focus prime lenses, so I always have full control over where and what I focus on. (The only exception is when I use the Nikon 18-35 mm FX lens for pole photography. It’s a nice, small, light wide zoom lens with autofocus, which I can control using my CamRanger. This will be the subject of a future post.)

While I used my ZEISS 35 mm f/2 manual focus lens to purposely create these two photos, they illustrate an issue I’ve seen when I get photographs from either police or other experts. This car was inspected in a small, crowded area of a tow yard. To photograph the entire front end, I had to use a wide angle lens, and crouch down in bushes and weeds. In this first photo, the weeds are in sharp focus, but the car is blurry. (Click on the image to see a larger version, then click on back arrow to return to the post.)

Focus on weeds in front of wrecked Taurus. (ZEISS 35 mm f/2 lens on Nikon D850.)
This can easily happen if the autofocus point happens to pick up a weed or anything else between the lens and subject. Unfortunately, no amount of sharpening or other post-processing can restore detail to the car itself.

This second photo has the car in proper focus, with the weeds out of focus in between the lens and car.

Focus on front of wrecked Taurus. (ZEISS 35 mm f/2 lens on Nikon D850.)
While you’re in the field shooting, it can be difficult to tell if your subject is in focus by looking at your camera’s LCD, unless you zoom in to 100% and scroll around the image. If you have unimportant elements between your lens and your subject, it’s best to either manually focus, or make sure you move your autofocus point onto your subject.

More on Fill Flash

Fill Flash helps bring out details in the shadowed area of high-contrast subjects. This 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.)
To bring out some detail, a flash was added at a reduced power output. Fill flash isn’t intended to light the entire image frame, but only to lighten very dark areas.
Left Front of Truck with Medium Fill Flash (ZEISS Milvus 50 mm macro lens on Nikon D850 with Nikon SB-910 flash.)
While there was a little more detail in the suspension and frame, raising the flash power added even more light under the fender.
Left Front of Truck with More Fill Flash (ZEISS Milvus 50 mm macro lens on Nikon D850 with Nikon SB-910 flash.)
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.

Fill Flash Adds Details

Fill flash helps bring out details in vehicle photos, especially under high-contrast lighting situations. As an example, the damage to the right front of this black car does not show up well when no flash is used. With the sun behind the car, the damaged area was in shadow. (Click on image to enlarge, then on back arrow to return.)

Front end damage with no flash used. (ZEISS Milvus 50 mm macro lens on Nikon D850.)
Obviously, this car couldn’t have been driven to a more favorable spot, and it was not possible to have it moved. Besides, even if the car was moved to get better light on the right front, then the light wouldn’t have been good from other angles.

Like everything else photographically, the solution is to think about the light. Where is it? (Fairly high, and coming from the other side.) Where do you need it? (Good top light, but need light in the foreground, too.) How can you get light where you need it? (Use flash to fill in the shadows.) This is called “fill flash”. The term fill flash means that flash isn’t the only light source illuminating the subject, but light from the flash just fills in the shadows as desired.

Here’s the same vehicle in the same location with the same light, but with an on-camera flash used to partially fill in the shadows.

Front end damage with fill flash used. (ZEISS Milvus 50 mm macro lens on Nikon D850 with Nikon SB-910 flash.)
You can see the light on the background stayed the same, but light from the fill flash now shows details in the shadows.

While at first flash may seem too complicated and unpredictable, learning to use it correctly is probably the best way to improve your vehicle, product liability, and testing photographs. Learning to use flash will be a big part of my SAE photography class: SAE Photography for Accident Reconstruction, Product Liability, and Testing.