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Equivalence is useful if you have any interest in light (and as a photographer, you probably should)

Filed Under News: Digital Photography Review

Photography is all about light, something you’ll quickly discover even if you’re not familiar with the word’s Greek origins. Most of the time, we use a standard framework (the standard exposure model) to discuss how much light your camera is receiving. However, this isn't the only way of looking at things.

'Equivalence' gives us another way of looking at light, that just happens to give a clearer understanding of the capabilities of different formats. It's a common misconception that equivalence and the more familiar standard exposure model are at odds with each other, but the two systems aren't contradictory – they just tell different parts of the same story.

The Standard Exposure Model

The standard exposure model uses shutter speed and F-number (the ratio of a lens’s focal length, relative to its exit pupil) to describe how much light your camera is receiving. Using this ratio normalizes the behavior of lenses based on how much light they project per unit area, meaning it works consistently across different focal lengths. The available light and the exposure you can devote to it tend to dictate most of the noise in your image, so are the most effective way of reducing it.

A third factor (which is applied after the light has been captured, so doesn’t affect exposure, per se) is sensitivity (ISO) which, at its most basic can be thought of as essentially ‘whatever amplification or brightening is needed to provide the expected image brightness from a given exposure.’ This has the effect of ensuring that the exposure system works, regardless of what format you’re shooting on.

Lightmeters are designed to express the light level in terms of the standard exposure model. Since this system is, by design, independent of format so are their results.

There are many benefits to this system. It means that you never have to think about what format you’re shooting with: everything from your smartphone to a medium-format back will work using the same settings in the same lighting conditions. This is the reason light meters are able to work without giving a fig for what camera you’ve got.

The main downside to this*, is that it obscures the effects of format. There’s nothing wrong with thinking in terms of exposure, but it leads to slightly wooly conclusions such as ‘full-frame sensors can give less depth of field and are better in low light’ which is generally correct but not very precise. In turn, this can lead to confusion about why this is the case. ‘Something to do with bigger pixels?**

Equivalence: the whole image perspective

Equivalence is simply a different way of looking at the same thing. Instead of thinking about light per unit area, it looks at the total amount of light that goes to make up the whole image. As a result, it assumes you're trying to take a specific picture (matched framing, shot from the same position) and also requires you to compare images at the same size. In other words, it’s about pictures, not pixel peeping.

It’s not a matter of faith, nor does it contradict anything that the exposure model says, it’s simply a question of geometry. In the film era, where most people used a single format and only a generally knowledgeable minority used medium and large formats, the same underlying effects were usually discussed in terms of enlargement. But, since there’s no fundamental link between the size of your pixels and the size you choose to view or print them, ‘enlargement’ becomes a slightly arcane way of thinking about it.

Equivalence is simply a way of looking at how much light a system gets, and just happens to use the 135 film format as the baseline for those comparisons (because it was the dominant system in the film era, which saw it being used as the basis of comparison for focal lengths, when the many and various sensor formats emerged at the beginning of the digital era).

Equivalence, the basics

Equivalent f-numbers are a means of considering the combined effect of the aperture and sensor size.

In the same way that equivalent focal lengths describe the effect of sensor size on the field-of-view a lens gives, equivalent apertures describe the effect of sensor size on the properties that aperture affects (depth of field, diffraction, total light projected). In both instances, the underlying properties are not changed: neither the focal length or F-number of a lens is changed by different sensor sizes, only their effects.

  • F-number = focal length/aperture diameter
  • Equivalent f-number = equivalent focal length/aperture diameter

Comparing equivalent apertures allows you to understand how much control a lens will give you over depth-of-field. It also gives a good idea of how low-light performance will compare between two cameras of different sensor sizes, since it tells you how much total light is making up the final image (most noise is most images comes from the amount of light captured).

However, because the exposure and ISO system is, by design, independent of sensor size, equivalent apertures should only be used to understand camera/lens capability, not exposure.

To keep things real-world relevant, equivalence assumes you're shooting the same framing from the same position and then viewing the images at the same output size.

Looking at total light or light per image, means we can better recognize the effect of light on depth-of-field, diffraction and noise. Rather than vaguely saying that ‘full-frame is, er, better than APS-C’ we can understand why and how much more or less light a larger or smaller sensor will receive at the same exposure settings (same shutter speed and same F-number), by calculating what the equivalent F-numbers are.

So, since a 50mm F2 lens used on APS-C behaves equivalently to a 75mm F3 lens on full-frame, we can see that a full-frame camera with a 75mm F2 could receive up to one and a sixth stops more light, if you opened the lens up to its maximum aperture. You can see this would give a shallower depth of field and a little over one stop of noise improvement, assuming comparable sensor performance.

Looking at it this way not only shows us the boundaries of the capabilities of each system but also gives us a meaningful way to assess whether either system is under or over-performing, relative to other systems, since it gives us a set of expectations about what it should be capable of.

This really shouldn’t be controversial

You do not need to consider equivalence for a moment when choosing an exposure. You do not have to multiply the F-number by the crop factor, unless you want to understand its behavior, relative to another system. However, it is completely legitimate to do so. The logic behind it is mathematically sound***, it holds up to real-world testing and it can be informative, if you’re interested. It’s an effective tool, whether you have need for it or not.

For more information, with real-world examples, read our more in-depth article on the subject.

* ...beyond the flexibility in the ISO standard that means cameras don’t actually have to produce the image brightness you expect, and the fact that ISO as used by camera makers has very little meaning in terms of Raw shooting. [Back to text]

** If you view two images at the same size, the ones taken with the larger sensor at the same field of view, F-number and shutter speed will usually be cleaner in close proportion to the sensor size increase, almost regardless of the pixel size. Whether you have the same number of larger pixels or a larger number of the same sized pixels generally makes very little difference. [Back to text]

*** As Andy Rowlands' Physics of Digital Photography points out, equivalence works at most normal photographic distances but, because it’s based on a slightly simplified depth of field equation, doesn’t hold true as you approach the close focus distances used for macro photography. This is equally true for focal length equivalence. [Back to text]


Blind portrait shootout: Sony a9 vs Canon 1DX Mark II vs Nikon D5

Filed Under News: Digital Photography Review

Photographer Michael Andrew of YouTube channel Michael the Maven has put together a 'Flagship Epic Shootout Review' video comparing the Sony a9, Nikon D5 and Canon 1DX Mark II. The full video is genuinely worth your time, but if you don't have 44 minutes to spend watching the full review, one section in particular is both fun and frustrating: the blind portrait test.

Like it or not, we all have implicit biases when it comes to comparing cameras—it's hard not to when you've spent thousands (or tens of thousands) on your kit. But is the camera you say you like best, the one that produces the images you like most? When it comes down to the camera, by itself, using its own color engine, do you prefer Nikon, Canon, or Sony?

That's what Andrew wants to help you figure out, bias-free, in this blind portrait shootout. He shot 12 identical portraits using all three flagship cameras, and he challenges you to rank them before you know which camera shot which portrait. The game is simple: grab a pice of paper and list it from 1 to 12, and then draw three columns labeled A, B, and C at the top. As the images pop up on screen, give your favorite a score of 3, your second favorite a score of 2, and your least favorite a score of 1.

"At the end, we'll add the scores to discover which camera's color science you prefer most," he says. "Don't give it too much thought [...] I did my very best to take a picture of the same model, in the same lighting conditions, with the same white balance, with the same exposure settings."

Which do you prefer?

It's a fun little game that can turn a bit sour at the end when you add up the final score... especially if you've ranked your personal favorite brand dead last. This has already happened to two of our staff here at DPReview, and it will probably happen to a few of you as well. And before you jump in with a "just shoot Raw" argument, our Technical Editor Rishi has a message for you:

While shooting Raw helps poor white balance issues, it’s not a panacea for a disagreeable color engine. Putting aside for a moment the convenience of using straight-out-of-camera JPEGs, Raw converters like Adobe Camera Raw (ACR) include camera-specific profiles that emulate the manufacturer’s various color modes, so if they’re not to your taste to begin with, the Raw conversions are also unlikely to be palatable.

Furthermore, ACR can’t emulate the multitude of non-linear, scene-dependent adjustments camera JPEG engines perform. Even the same colors are not necessarily processed in the same manner in a landscape as it is in a portrait. It’s hard for Raw converters to emulate these complex adjustments unless the manufacturer works directly with them to directly share what they’ve learned over decades of color research.

So jump in, take the test, and let us know your scores (and whether or not you betrayed your go-to camera brand) in the comments.


500px adds support for wide-gamut color profiles and Google WebP format

Filed Under News: Digital Photography Review

Photography sharing and community website 500px has announced support for both Google's WebP format and wide-gamut images, as well as the ability to search based on color profile. According to 500px, the additional support reportedly reduces bandwidth usage by up to 25% while simultaneously enabling the service to offer images that are "truer to the photographer's original vision."

Until now, 500px's image hosting service worked by converting uploaded images, when necessary, from their non-sRGB color profiles to sRGB. The rise of wide-gamut displays, though, has paved the way for expanded color profile support. As of this update, 500px can deliver photos in sRGB, Display P3, Adobe RGB and ProPhoto RGB.

"Though sRGB has been standard in our industry for many years," said 500px VP Kelly Thompson, "with today's broad adoption of iPhones and wide-gamut displays, we can finally showcase each image in a more true-to-life way and allow searching by color profile."

As far as WebP support goes, 500px explains that it has been rolling out support for this format on Chrome browser over the last month. The format reduces file sizes while offering comparable or improved image quality. The newest version of the 500px Android app features WebP support.


DJI releases mandatory firmware for DJI Spark: update by September 1st… or else

Filed Under News: Digital Photography Review

Chinese drone maker DJI is releasing a mandatory firmware update for its DJI Spark drone, forcing all Spark owners to update their drone's software by September 1st. Any Spark drone not updated by that date will be grounded remotely.

The update brings multiple changes, but the reason it's 'mandatory' is that it contains a fix that prevents the drone from shutting down while flying.

The announcement was made in a newly released statement from DJI, which explains that it decided to disable any Spark drones that aren't updated in time "in order to maximize flight safety and product reliability." All Spark owners will be prompted to update the drone upon opening the DJI GO 4 App, though owners can also run the update through the DJI Assistant 2 desktop software.

In addition to fixing the safety issue, DJI explains that this new update improves the drone's battery management system, providing optimized power when the drone is in flight. Spark also gains full DJI Goggles integration support via this firmware, as well as an improved PalmLaunch functionality, better QuickShot Drone mode accuracy and increased remote controller compatibility.

Press Release

DJI Spark Firmware Update Enhances Flight Safety

DJI will be releasing a new firmware update this week to further enhance flight safety and performance of the DJI Spark.

The new firmware update enhances Spark’s battery management system to optimize power supply during flight. In addition, the new firmware has added support to fully integrate Spark with the DJI Goggles, optimized the PalmLaunch function for better stability after takeoff, improved the accuracy of controls under the QuickShot Dronie mode and enhanced the compatibility of the remote controller when syncing up with new firmware updates.

When prompted on the DJI GO 4 App, users with internet connectivity will be able to download the new firmware to update their aircraft’s and battery's firmware. The aircraft and battery firmware updates can also be done via the DJI Assistant 2 desktop software. If the firmware of either the aircraft or the battery is not updated by September 1, Spark will not be able to take off. DJI decided on the option of a mandatory firmware update in order to maximize flight safety and product reliability which we consider as top priorities.

The update comes after DJI released new features for its Spark in early August to deliver a more powerful combination of video and photo improvements including a new gesture to start and stop video recording and enhanced QuickShot video features for more cinematic control.


Godox’s smartphone app can now control all Godox wireless flash units

Filed Under News: Digital Photography Review

The app offers control of 15 groups of flashes with 32 channels to work with.

Chinese flash manufacturer Godox has updated its smartphone app so that it can be used to control the output of all of its wireless X flash units. Originally designed to control the new A1 smartphone flash unit, the newest version of the GodoxPhoto app can now be used with all the company’s X wireless flash units, as well as Godox wireless LED lights.

With accompanying firmware updates for the X1T commander units, it appears that the app sets the power output of the flashes under its command while the X1T transmitter simply gives the order to fire.

In a further update, Godox has made a number of its flash units multi-brand compatible, so that the same unit can be used with a range of X1T controllers and flashguns in commander mode that are designed for brands other than that of that particular flash. For example, the V680 ll N, which was designed as a Nikon compatible flashgun, can now be used with Canon, Sony, Panasonic/Olympus and Fuji cameras when those cameras are fitted with the appropriate X1T controller or a dedicated flash in commander mode.

For more information see the Godox website, or download the app for yourself on the iTunes App Store.


New Western Digital MyBook Duo offers up to 20TB of storage… for $800

Filed Under News: Digital Photography Review

Earlier today, Western Digital introduced its new My Book Duo external desktop storage system, which offers up to 20TB of storage capacity and RAID capabilities.

The My Book Duo connects to your computer via a USB Type-C port and supports USB 3.1 Gen 1/3.0/2.0 for high-speed connectivity. Additionally, the device comes with two USB Type-A ports for connecting other accessories such as drones, cameras, card readers or smartphones for syncing and charging.

The MyBook Duo also features RAID-optimized WD Red hard drives, to deliver sequential reads at up to 360 MB/s. The RAID-optimized firmware comes with auto management of drive operations to help ensure read/write cycle data integrity. Password protection and 256-bit AES hardware encryption with integrated WD Security software come standard as well.

The MyBook Duo is now available globally. US Pricing ranges from $260 for the 4TB version up to $800 for 20TB variant. More information is available on the Western Digital website.


New Sony Alpha a6500 firmware improves image stabilization in movie mode

Filed Under News: Digital Photography Review

Sony has released new firmware for its Alpha a6500 24MP APS-C mirrorless camera. Version 1.04 of the camera's internal software improves performance of the image stabilization system when shooting video and can be downloaded and installed from the Sony Support website now.

As usual with Sony, you'll have to select your computer operating system before downloading the firmware file. Also make sure, you have at least 500MB available hard drive space and 512MB of RAM.


Intro to drones part 2: How to choose your first drone

Filed Under News: Digital Photography Review

So, you're ready to buy your first drone. Great! But what to get?

In this article, we'll discuss criteria to consider when buying a drone so that you can find the model that's right for you. We'll also make a few recommendations based on different use cases.

Note that this is the second in a three-part series. In Part 1, we reviewed drone basics such as technology and terminology. In Part 3, we'll cover what you need know in order to fly safely, as well as the difference between recreational and commercial flying.

Choosing the drone that's right for you

Before all else, consider how you plan to use your drone. Are you a selfie king or queen who wants to post pictures on social media, an adventurer looking for a unique shot, or a professional who demands the highest image quality?

Once you've answered that question it's time to start looking. That's a lot easier to do once you understand the range of options available, so let's dive in and look at features you should think about before buying a drone.


Size is an important factor since it impacts portability and convenience. When it comes to 'Buy&Fly' drones, sizes range from models small enough to fit in a cargo pocket to those requiring a small backpack or case.*

There's some truth to the saying, "The best camera is the one you have with you," and it's true for drones as well. If having a drone with you at all times is of paramount importance, look for a very small model like the Hover Camera Passport that fits in a pocket or handbag. You may give up some high end features in exchange for convenience, but you'll be able to pull out your drone at a moment's notice.

The Autel Robotics X-Star Premium packs in a lot of premium features at a competitive price.

Compact drones, like the DJI Mavic and GoPro Karma, are the Goldilocks of the drone world, which explains their rapidly growing popularity. They provide features found in larger models while remaining small enough to be a good choice for activities like travel, hiking, or adventure sports.

Larger drones, such as the DJI Phantom series or the Autel Robotics X-Star Premium, will generally deliver the best specifications and often include some type of marquee feature such as a camera with a larger sensor, a removable camera, or even a hexacopter option. While they're usually feature-rich, they may require a dedicated pack or case for travel.


When it comes to flight, weight is paramount, so drones use cameras with smaller sensors (which require smaller lenses). However, there are important differences between models.

Some drones to use very small sensors, similar to what you would find in a mobile phone. The Hover Camera mentioned above uses a 1/3.06" sensor, but that's part of what allows it to stay small. The most common sensors used in drones today are probably the 1/2.3" variety, also found in many consumer-oriented compact cameras. At the high end you can find 1"-type sensors similar to those in a premium compact camera, such as the Sony RX100 series.**

Shutter type is important as well: some models, like the DJI Phantom 4 Advanced, include a mechanical shutter that can eliminate rolling shutter artifacts when taking photos.

The camera on the DJI Phantom 4 Pro and Phantom 4 Advanced use a 1"-type sensor similar to what is found on premium compact cameras.

Finally, consider recording formats. Many drones can capture Raw images in addition to JPEGs, and 4K video is common as well. Video shooters take note: if high quality video is important to you, look beyond resolution and consider frame rates, bit rates, and codecs as there are differences.


Absolute performance when it comes to things like speed an maneuverability may be important if you want to shoot fast moving subjects like action sports or moving cars. If that's your use case, pay attention to specs like maximum speed, though be aware that on some models, flying at maximum speed can result in the drone's rotors creeping into the frame.

Most drones have a claimed battery life in the range of 15-30 minutes. In the real world you'll probably get something less than that, particularly because it's a good practice to land your drone with some battery power remaining. Altitude, ambient temperature and wind speed are the three largest factors in determining actual flight time.

Many drones claim to have long operating distances, sometimes in the range of several miles. Keep these claims in perspective. Operating range will depend on many factors, but you should have your drone in visual line of sight at all times, so it's unlikely you'll be flying that far anyway.

DJI Phantom 4 Pro batteries are rated for approximately 30 minutes of flight time, though in practice you'll probably get a bit less.

Transmitter type

Drones aimed at enthusiasts have dedicated controllers that provide a standard interface, allow for precise control, and usually have dedicated hardware buttons or switches for important functions. Dedicated controllers allow for longer range operation as well. If your goal is to shoot high quality photos or video, this is your best option.

Smartphone-only controls are common on mini or 'selfie' drones, and their range is measured in meters rather than kilometers. If you want to stash your drone in a pocket so you can pull it out for a family photo at the beach, this is a good option. Many drones are designed to react to gestures and hand signals as well, making the controller less critical for certain tasks.

Some models take a hybrid approach. For example, the DJI Spark is designed to work from your phone, but can optionally be paired with a controller for extended operation.

The DJI Spark can be controlled by gestures, a mobile device, or an optional dedicated controller.

Automated flight modes

Automated (or 'intelligent') flight modes can be tremendously helpful by handling some aspects of flight control while you focus on creative decisions. Many of these modes are almost standard features at this point. But do you need them?

If your primary focus is still photography, look for models that have dedicated photo modes for tasks like shooting panoramas or stitching together vertical shots. Camera controls such as manual exposure modes or auto exposure bracketing can also be useful.

For video, automated flight modes can make a world of difference, making it much easier to do things like tracking a subject. The smooth motion these modes provide can also make your footage look more cinematic.

Collision avoidance systems

Collision avoidance (or obstacle avoidance) is not a substitute for attentive piloting, but can be helpful avoid collisions with objects such as buildings. These systems can also be helpful if you need to navigate tight spaces. To learn more about how these work, refer to Part 1 of this series.

The most common variety of collision avoidance sensors are those that look forward in front of the drone, however some models have rear and side facing sensors as well. If you're nervous about running into something, look for a model with collision sensors. But remember, they are not infallible.

Sideways facing obstacle sensors on the Phantom 4 Pro.


Notice that this section is called 'budget' and not 'price', and that's an important distinction. You'll probably need to budget for at least some accessories.

At the top of the list are batteries, and there's a wide range of prices. For example, additional batteries for an Autel Robotics X-Star Premium cost $99, while batteries for a DJI Phantom 4 Advanced are closer to $170. Add two or three batteries and the costs add up quickly. Frequent flyers may also want a charging hub to keep those batteries topped up.

Other costs can include filters (ND or polarizers), micro SD cards, replacement parts like rotors, and for larger drones a carry case or backpack with inserts to support your model.

*For the purposes of this article, we're ignoring the dozens of very inexpensive (and practically disposable) micro-drones that are basically toys, nor are we addressing high end professional products aimed at commercial cinematography. Works for me, I think we should stick to Phantom size and smaller, I just wanted it all out there!

**If you want to go larger than 1"-type sensors, it's possible to get models with Micro Four Thirds cameras, or those that can carry a DSLR or cinema camera, but those are beyond the scope of this article.


NASA captured photos and video of the ISS ‘photobombing’ today’s solar eclipse

Filed Under News: Digital Photography Review

The International Space Station, with a crew of six onboard, is seen in silhouette as it transits the Sun at roughly five miles per second during a partial solar eclipse on Aug. 21, 2017 near Banner, Wyoming. Photo credit: NASA/Joel Kowsky

Plenty of people were pointing their cameras up at the solar eclipse today, but leave it to NASA to capture a little something extra. From his vantage point in Banner, Wyoming, NASA photo editor Joel Kowsky captured a dual eclipse of sorts: the moon obscuring the sun, and the tiny pinprick of the International Space Station obscuring a little bit of what was left.

As the ISS and its six crew members flew in front of the partially obscured disk of the sun, Kowsky had both still and slow motion video cameras trained on his target.

Here's a closer crop of the photograph above:

Here, a composite that shows the ISS's full transit across the partial eclipse:

And, finally, a slow motion video of the transit, recorded by Kowsky at 1,500 frames a second:

To see these photos and video in their full glory, head over to the NASA Goddard Space Flight Center Flickr account.

All photos and video courtesy of NASA/Joel Kowsky


NASA captured photos and video of the ISS ‘photobombing’ today’s solar eclipse

Filed Under News: Digital Photography Review

The International Space Station, with a crew of six onboard, is seen in silhouette as it transits the Sun at roughly five miles per second during a partial solar eclipse on Aug. 21, 2017 near Banner, Wyoming. Photo credit: NASA/Joel Kowsky

Plenty of people were pointing their cameras up at the solar eclipse today, but leave it to NASA to capture a little something extra. From his vantage point in Banner, Wyoming, NASA photo editor Joel Kowsky captured a dual eclipse of sorts: the moon obscuring the sun, and the tiny pinprick of the International Space Station obscuring a little bit of what was left.

As the ISS and its six crew members flew in front of the partially obscured disk of the sun, Kowsky had both still and slow motion video cameras trained on his target.

Here's a closer crop of the photograph above:

Here, a composite that shows the ISS's full transit across the partial eclipse:

And, finally, a slow motion video of the transit, recorded by Kowsky at 1,500 frames a second:

To see these photos and video in their full glory, head over to the NASA Goddard Space Flight Center Flickr account.

All photos and video courtesy of NASA/Joel Kowsky