What is equivalence and why should I care?
1 Depth-of-field equivalence
The concept of 'equivalence*1' is still somewhat controversial and not always clearly understood. We thought it was about time we explained - and demonstrated - what equivalence means and what it doesn't.
What is equivalence?
Equivalence, at its most simple, is a way of comparing different formats (sensor sizes) on a common basis. This is already the way most lenses are talked about: it's quite common to say that a compact camera includes a '28-120mm lens' but the key and (often unspoken) word in that description is 'equivalent.' It's a simple way of describing the range of fields-of-view that the lens offers, cancelling out the effect of sensor size by using a common reference point.
A 100mm equivalent lens on a small-sensor camera will give the same framing and (because that means shooting from the same position) the same perspective as an actual 100mm lens does on a full frame camera, regardless of sensor size, because they are equivalent.
|Crop factor||Focal length||Diagonal Angle
of View *2
|Canon EOS-1D X||Full Frame (864mm2)||43.3mm||1||100mm||24.4deg|
|Olympus OM-D E-M5||Four Thirds (224mm2)||21.6mm||2||50mm||24.4deg|
It's this logic that the idea of 'crop factors' is based on. The 'Four Thirds' sensor format has a diagonal very close to half that of a 'full frame' sized sensor. And, sure enough, if you calculate the angle-of-view of a 50mm lens on a system with a crop factor of 2, it's the same as for a full frame camera with a 100mm lens.
|Equivalence helps compare different lenses and cameras by using 35mm 'Full Frame' as a reference point. This doesn't mean that Full Frame is the best, or even the optimal format, it's just a reasonably well understood point of comparison.|
However, it's not just focal lengths that can be thought of in equivalent terms. In our recent reviews of fixed-lens cameras, we've tended to include a chart showing 'equivalent' aperture values and how they change as you progress through the zoom range. In the rest of this article, we'll discuss and demonstrate how apertures and sensor sizes interact.
The reason we do this is because it's become quite common, for any given part of the market, to have to choose between cameras with different lenses and sensor sizes. This wasn't such a common problem in the film era since 35mm was the de facto standard. As such, most people didn't need to directly compare quality and characteristics across those different formats. 35mm was better than 110, medium format was better again and large format was still better. In the digital era, the significance of (and difference between) sensor sizes isn't always appreciated, not helped by a rather opaque naming system.
Apertures and F-numbers
It turns out, the relationship between sensor size and aperture is very similar to that between focal length and sensor size. It's the physical size of the aperture that defines depth-of-field, not its F-number. Two lenses offering the same angle-of-view with 25mm diameter apertures will give the same depth-of-field of shot at the same shooting distance and when viewed at the same output size.
So, let's consider the effect of that 25mm aperture in the lenses we've been discussing. Both lenses give the same angle-of-view, so you're likely to shoot them with the same shooting distance - since that way you'll get the same framing in both photos.
Now think about what that means in terms of F-number (focal length/aperture diameter). The 25mm aperture in the 100mm lens would be considered to be f/4 (100mm/25mm), whereas the same-sized aperture in the Micro Four Thirds lens would be an f/2 (50mm/25mm). The table below shows the calculated depth-of-field for the two lenses, shot at the same working distance:
|Camera||Focal length||Aperture diameter||F-number||Depth of field *3||Equiv.
|Canon EOS-1D X||100mm||25mm||f/4||Near 16.1m
|Olympus OM-D E-M5||50mm||25mm||f/2||Near 16.1m
As you can see, although the lenses are quite different, the 50mm f/2 lens is giving the same framing and the same depth-of-field as a 100mm f/4 lens is on Full Frame. As such, you can say that a 50mm f/2 for Micro Four Thirds is equivalent to a 100mm f/4 Full Frame lens in terms of both field-of-view and depth-of-field.
We don't expect you to take our word for this. Conveniently, it's become fashionable for manufacturers to produce 85mm equivalent, F1.2 lenses, which makes it relatively easy to show the ways in which they are, and aren't equivalent. We'll demonstrate this on the third page of this article.
*1. Not to be confused with 'Equivalents' - an influential series of abstract photographs by Alfred Stieglitz, and an approach to photography that they inspired.
*2. Calculated using TawbaWare's Angular Field of View calculator
*3. Calculated using DOF Master, with the lenses specified, focused to a distance of 20m
Jun 27, 2017
Jun 22, 2017
Jun 15, 2017
Jun 15, 2017
|Douaumont Ossuary by Eric 54-BNF|
from Armistice Day
|Silhouette at sunset by Jill Hancock|
from Portrait Lens (around 80mm or equivalent - please check the full rules)
Sigma is discounting 13 different high-performance 'Art' series lenses from today until November 30th. The company is calling it an 'unprecedented' sale.
See DJI's 'AeroScope' drone-tracking technology in action. This is the system that DJI says can help law enforcement and airport (among others) track and identify rogue drones.
iPhone X owners can already accessorize their new phone with high-quality smartphone photography lenses courtesy of Moment's new lineup.
Considering buying Sigma's exciting new 16mm F1.4 DC DN Contemporary lens for crop-sensor E-Mount and M43? Check out these official full-res samples first!
Vimeo has just added support for 8K HDR 10-bit content, making it possible to show up to 75% of the colors the human eye can perceive vs the usual 35%. Take THAT YouTube.
The holidays are coming, but your gear isn't cutting it? It's time to treat yourself!
We're counting down our top 10 most popular sample galleries of 2017, and sitting pretty at #5 is the Fujifilm X-T20.
See some of the most iconic black-and-white photographs throughout history brought to life by a community of colorization enthusiasts and professional retouchers in the new book Retrographic.
Shopping for a photographer? Whether you are one yourself or not, chances are you could use some ideas. From stocking stuffers on up, we've got some photography gift suggestions for every budget.
We're counting down our top 10 most popular sample galleries of 2017. Drum roll please... the #6 spot belongs to none other than the Sigma 85mm F1.4 DH HSM Art.
Read the story behind this gorgeous wedding photo captured at Trolltunga in Norway by husband and wife duo Priscila Valentina Photography. The 14 hour hike in the rain that preceded this shot was TOTALLY worth it.
Go behind the scenes with filmmaker Nick Arcivos, who recently created a beautiful cinematic short film in Paris using only the iPhone X, a couple of gimbals, and a few lights. The results are very impressive.
A Bay Area startup offering a pay-by-the-photo camera service cleverly addresses the pain points photographers experience when they pick up their first DSLR. But can it survive the smartphone?
It's been a big year for software innovations, dual cameras and huge displays. Take a look at our picks for the top smartphone cameras and why we think they stand out.
We're counting down our top 10 most popular sample galleries of 2017. At the #7 spot is the ready-for-any-weather Olympus Tough TG-5.
By combining his skills as a time-lapse filmmaker and an engineer, Julian Tryba created this out-of-this-world creative 'layer-lapse' of New York City that alternates between night and day in time with the music.
Canon Japan's new lineup of novelty camera-themed gifts was just revealed online, including a lens mug and lens thermos, two retro camera-themed USB drives, and a picnic mat.
The Profoto A1 most certainly isn’t for everyone [...] But for those who are used to using the Profoto systems, and want something that pairs seamlessly with the strobes you already have, there is no better companion.
Fujifilm has asked a US district court to clear it of any wrongdoing, after allegedly being threatened with trademark litigation by Polaroid.
While a couple of our reviewers are out testing the Sony a7R III in Arizona, back in Seattle we slapped the camera in front of our studio scene to get a close look at its image quality. See how it stacks up against the competition.
We're counting down our top 10 most popular sample galleries of 2017, and the #8 ranking belongs to the Nikon D7500.
B+W has announced a new aluminum filter holder that offers three slots so users can use multiple filters at the same time. The holder goes with the 2mm thick 100mm square filters it launched earlier this year.
8K video is coming a lot faster than you think, and Blackmagic is ready for it. Meet the DeckLink 8K Pro, a new high performance PCI-E capture and playback card built to handle 'real time high resolution 8K workflows.'
"Glass is everywhere in photography. From Eugène Atget’s reflective vitrines to Lee Friedlander’s sly self-portraiture, photographers have long been in thrall to the visual complications glass can inject into a composition."
Former Apple Aperture lead developer Nik Bhatt has designed an iOS app called RAW Power that lets you edit raw photos from your professional camera using your phone and tablet.... color us intrigued.
Advertising photographer Blair Bunting got his hands on the new Microsoft Surface Book 2, and it blew him away. Bye bye MacBook Pro...
The OnePlus 5T retains many of the 5's features and specs, but comes with an edge-to-edge display and a dual-camera that is optimized for low light.
Sony's recently announced IMX461 backside illuminated medium format sensor will bring 100MP resolution and almost 2x the speed to the next-gen Fuji GFX and Hasselblad X1D.
With the ‘Rent a Hasselblad’ camera equipment renting program, the camera makers is aiming to give enthusiast and professional photographers easier access to its medium-format photography products.
They say seeing is believing, and that's exactly what happened when one DPR staffer took the Google Pixel 2 out for an afternoon shooting under challenging conditions.