Why the Camera Industry Clings Onto the Design of Early SLR Bodies


Have you ever wondered why the professional photography industry is dominated by cameras that carry on the design tradition that was started by classic film SLRs?

Diagram of a pentaprism

Diagram of an SLR pentaprism

Early SLR design was dictated by the need to integrate a pentaprism (as well as the abnormally fast and large shutter mechanism for a camera that size). However, as time went by, the SLR design became more ergonomical in nature, easier to grasp and stabilize solely by hand, with the aid of the forward-jutting grip and the sufficiently long lens. Handheld SLRs are many times more stable than rangefinders or viewfinders from the same time period.

When digital cameras first appeared, the available display technology was deficient when compared to the “resolution” achieved by simply projecting the image entering the camera via a mirror into a focusing screen (usually, a round piece of ground glass, although some designs used fresnels) that would then be reflected by a pentaprism (or pentamirror). So, it’s natural that, from the start, DSLRs retained the traditional SLR bodies, with some minor changes, namely, being a little bulkier than regular SLRs, to fit inside all the electronic components.

Even today, any photographer (and videographer) who is worth his salt will prefer looking into the eyepiece than at an exposed display, at least during framing, exposure, and focusing, because incident light on the display (glare) will reflect on to your eye, making it difficult to see what the image actually looks like.


Using a pentaprism still has many advantageous features that make them better than digital displays, although they don’t hold the same degree of truth they did 10 years ago:

  1. When using an optical viewfinder, you are sampling EVERY light ray that hits the focusing screen, and not only the ones that hit a pixel sensor. Provided that your camera’s focusing array is in good condition, the eyepiece will display a very faithful representation of what your scene actually looks like, in regards of color and brightness. Nowadays, displays (and sensors) have resolutions and dynamic ranges that approach that of the human eye, but we are not quite there yet.
  2. Contrast detection autofocus is deficient when compared with phase detection focus on SLRs and the good old “something is wrong” approach of the human eye. Contrast detection is slower, and does not operate properly under low light conditions. Contrast detection is common to mirrorless cameras.
  3. This one might seem like a minor point, but not having a mirror in front of the sensor really leaves your sensor exposed to debris and dust. I clean my camera’s sensors (with the menu option, of course. NEVER clean a sensor by hand) each time I use them on the field, and, most of the time, the mirrorless camera is the one that needs servicing because of the sheer amount of dust that gets stuck on the exposed sensor. This is something that will never change.

Sony’s SLT line of cameras use a modified SLR design: Instead of having a completely opaque mirror, the camera’s use a semi-translucent mirror set at a 45 degree angle. When light hits the mirror, it is directed towards two different sensors: One set directly above the mirror, where the focusing array would be, which is used for phase detection focus and exposure, and the second one behind the mirror, where a normal sensor would be, for imaging.

The design of Sony's Single Lens Translucent (SLT) cameras

The design of Sony’s Single Lens Translucent (SLT) cameras

The SLT design uses the image rendered by the imaging sensor for displaying, dumping completely the optical approach to focusing/framing. Mind you, the SLT line was designed especially with filming and video in mind (which makes them my favorite line of DSLRs), and most, if not all, professional photographers would rather use the regular SLR design with pentaprism.

So, there are three basic reasons we cling to the old SLR design:

  1. Technology: the eye, and pure optics, are still the best way to get a faithful image for focusing and framing. Sensors and displays are not quite there yet.
  2. Ergonomy: The GH line of mirrorless cameras by Panasonic uses the SLR design. Sturdier and easier to handle and stabilize than the viewfinder or rangefinder design, this is, I believe, the main reason why we still use the SLR design
  3. Tradition: The photography crowd is one that does not embrace paradigmatic change with ease. Optics is an old science, perhaps one of the oldest studies of physics. The adoption of new technologies involving optics would require a very objective upgrade from the older model, especially when you consider how much money one invests in collecting all the necessary equipment for photography.

    Unlike other areas of digital technology, photography does not require one to change equipment every year. A Canon T2i bought 4 years ago is still a very respectable piece of equipment when used properly. So, letting go of a design that has worked perfectly for photographers for the past 60 years and that has yet to be replaced by a significantly better design is not an easy thing to do, especially when you consider the costs of embracing a new model.

About the author: Diego Noriega Mendoza is an amateur photographer and aspiring filmmaker based in Mexico City, Mexico. You can find him on Twitter and Facebook. This article originally appeared here.

Image credits: Film star by APM Alex, Pentaprism by avikovacevich, Wide angle viewfinder by Lars Plougmann

  • thenewno12

    Why are you scared to clean your sensor by hand? As long as you are careful it’s totally fine and way more effective than any menu based option.

  • Kay O. Sweaver

    While I understand all the technical reasons for retaining the mirror, prism, etc. I’m not convinced that the form factor has to stay the way it is. There’s no film canister or uptake required in the body anymore. Personally I’d welcome a redesign with a better grip. I think the adjustable grip on the C100 is a good start. After a long day of shooting on a conventionally shaped DSLR without a battery grip my wrist is in some serious pain.

  • gochugogi

    Everybody’s hands and gear are different, so it’s important to buy gear that fits your hand. Some grips–mainly small ones–cramp up my hands while large contoured ones are good for hours. Maybe you should try a Kirk Sports Grip. A lot more comfy and natural for long sessions outside.

  • JoeNoName

    I love the Sony grips, its almost magnetic and sticks to your hand as a glove. Watch images and compare Sony a77 vs Canon vs Nikon. Your wrist might be in pain because of the weight of the camera rather than the grip, but oh well…

  • Dave

    “Even today, any photographer (and videographer) who is worth his salt
    will prefer looking into the eyepiece than at an exposed display…”

    Uh, ok. Thanks for letting us know what we should prefer, I guess.

    “When using an optical viewfinder,[…] the
    eyepiece will display a very faithful representation of what your scene
    actually looks like, in regards of color and brightness.”

    While this is true, it is often more desirable to see what the sensor sees and is going to capture. No camera optics are going to beat your eyes in regards to colour and brightness.

  • Will Mederski

    Though you’d probably be tackled in 30 seconds flat if you “shot” in public with it, I’ve always thought using the design elements of a rifle butt / pistol grip would really offer the best handheld stability for photography.

    Sucks things that shoot bullets kinda ruined that one for us…

  • uksnapper

    The film slr style is not user friendly.
    You have to turn your head sideways to look through the viewfinder while squashing your nose to get close enough.
    The only comfortable slr I used was the old Rollie 3003.
    Low budget digital cameras seem to have good body designs with lenses offset to the side like the (now) old Minolta Dimage 7 and of course the medium format slrs were and still are relatively easy to use

  • wickerprints

    The real advantage of peering through a viewfinder is that the resulting position stabilizes the camera and therefore aids in composition. If you are holding the camera out in front of you at arm’s length, it is much more difficult to maintain accurate subject framing. Of course, that is not to say there aren’t other benefits–but to me, this is by far the primary reason for the viewfinder in handheld situations, regardless of whether it is TTL, eye-level, or waist-level.

    The SLR design paradigm is already being slowly supplanted by alternative technologies, but the primary reason for its long-held dominance has always been about two basic components: TTL viewing and AF. The former is being replaced by electronic viewfinders, and the latter will eventually be superseded by on-sensor phase detection AF and/or contrast detection AF, once processing power results in response and accuracy rates comparable to existing phase-detection AF systems. The weakness of existing AF systems is that they are intrinsically limited by the geometry of the mirror box and the size of the secondary AF mirror.

    We are clearly not there yet. Professional photographers will not give up cutting edge VF/AF technologies in modern DSLRs unless an alternative is developed whose advantages clearly outweigh any shortcomings. An optical viewfinder has zero latency, but it could be argued that the purpose of the viewfinder is not to show you what your eyes see, but what the sensor itself sees, complete with its limitations of dynamic range and color accuracy.

  • aa
  • Jeremiah

    Not to mention that optical is useless in the dark, when using high ISO or long exposures you can literally see in the dark with the sensor and display. Auto focus is also pretty useless in low light, but manual focusing with the display is pretty easy.

  • Alastair Ross

    You should have a look at and You can still find old soviet Zenit Fotosnipers on ebay too.

  • Diego Noriega

    While there are several sensor-cleaning options on the market, I steer clear of them, because of the very present risk of the solution leaking behind the IR filter and lodging itself between the sensor and the filter. While expert or steady hands may be able to bypass the issue, the simple fact is most people aren’t handy enough with the tools provided with sensor cleaning kits. I’ll be sure to add on my next post an exception to those people who are able to clean the sensor themselves. Thank you for your feedback.

  • Diego Noriega

    I do a lot of astronomical photography. I relied heavily on my OVF when framing and focusing for the nightsky, which, under ideal conditions, requires long exposure. When I first bought my A77, my biggest (and only) disappointment was that, since the sensor lacks the sensitivity and range of the human eye, I was unable to frame my pictures without kicking the ISO up to 25600, at which point the noise made it almost as difficult.

    In short: I disagree with your statement. Optical in the dark is superior to EVF anytime. For autofocus, cameras with IR illumination or Ultrasonic emission (Active AF) can bypass the lack of light necessary for Phase focusing.

  • TSY87

    It’s really not that bad… Just make sure the fluid you are using is meant for sensor cleaning. The eclipse fluid I use really leaves no residue and evaporates very fast. If all you do is use the cameras “sensor clean” function, your sensor will never truly be clean.

  • YouDidntDidYou

    3 micro four thirds cameras, 700,000 shutter actuations in 5 years, frequently change lenses in the field… Cleaned one sensor once! We have the technology…

  • TSY87

    the fact that you still had to clean one sensor at least once proves that the onboard cleaning system (vibrating the sensor) is not perfect. That being said, I am impressed. I have not had that kind of luck with my d700, d3s and d800. All had to be cleaned within 10k shutter actuations.

  • Jeremiah

    I won’t argue about astrophotography – it’s a very specific case. But i was comparing optical SLR viewfinders to the large LCD displays on the back of the camera – in my case on a Canon 7D – not electronic viewfinders like on an A77 which i haven’t used.

  • geodesigner

    > Olympus OM
    > “Early SLR design”
    > Pick one.

    In all seriousness, even though the SLR design is no longer technologically justified, they’ve reached a mechanical / technical apex that is currently unparalleled in camera design history. It’s a vey refined mechanism. It serves its purpose very well, and it has evolved dramatically since its inception. I’d go out on a limb and say that SLRs evolved more in the last 50 years of the 20th century than combustion engines. Compare an old Exakta to an OM-1, and then to an F6.

    As soon as Electronic Viewfinders start offering zero latency and become more energy-efficient, it’s game over for pentaprisms. And even then, I’d bet that the traditional SLR shape would still be ubiquitous. It’s pervasive. It’s attached to an unconscious collective notion of what a camera should look like. The “Camera” button on apps is an SLR shape. It’s what we expect from a camera. An ur-typ, or a rheme if you will – more than just a shape, it’s a sign, it symbolizes and signifies “camera”.

    Yeah, I’m getting all semiotic on ya ;)

  • Monteraz
  • Adam Cross

    If I relied on ultrasonic vibrations to clean my sensor I would spend most of my editing time cloning out spots of dust! Though the first time I cleaned my sensor myself it was pretty scary! turned out perfectly though, I’ve cleaned it 3 times since then in the past year – if I had gone to someone to do it “professionally” I would’ve spent £240 on sensor cleaning all together!

  • tadeo

    wait! what??? what do you mean with “more stable”?? a mirror slapping up at high speed brings you a sensible handshake every picture you take!!! just compare it to a rangefinder that uses leaf shutter.
    i should also suggest that old designs are not perfect at all in many senses. a focal plane shutter for example brings you a very limited flash sync speed as the cost of more economical lenses.
    the perfect pro camera should be a live-view capable camera with leaf-shutter interchangeable lenses. that will give you no-shake with awesome sync speeds so you can get useable shots at the most varied shooting scenarios.

  • Mark Dub

    I can imagine getting beaten down by cops if I was carrying this thing, let alone aiming it

  • Burnin Biomass

    They sell mounts like that for your camera (I had a brochure for one, lost it, forgot who makes them). Plus, there was the Zenit Photosniper film camera.

    You are right, you would be getting too much bad attention of you were using it in public.

  • E

    Leaf shutters are however slow (typical max 1/500) and either an expensive solution (one shutter per lens) or limits the number of supported lenses if the shutter is integrated in the camera body.

  • Rob S

    Or how about because it just works. The basic bicycle hasn’t changed significantly since the 1890s. Why? Because it works. The modern automobile is 100 years old. Why? Because it works. The modern jetliner dates to the 707 from 1958 and the best selling 737 dates to 1967….because it works.

  • someone

    I’ll stick to my Rangefinders and TLR’s thank you. You can keep your slrs.


    own camera now has Dust reduction system… why we have to worry about sensor getting dirty?… i have e-p3 for close to two years.. changing lens almost everyday without any problem…

  • HasselbladSales

    Maybe try the Hasselblad Lunar? I hear their grips are unbelievable!

  • mokleTkcuF

    The need to clean a sensor is dependant on – frequency of changing lenses, how the lenses are changed and the environment in which the camera is used.
    I’ve been on a few overland safari trips in africa, and would have been unwise indeed not to take a sensor cleaning kit.
    Yet my studio camera has never needed a clean.

  • mokleTkcuF

    Digital autofocus and manual focus has been a real fiddly frustration for me. That’s why my Olympus OM-D, as much as I love it for many reasons, now sits in my glovebox as backup/snapshot camera, only.

  • TedCrunch

    I never use any solution when cleaning the sensor. I use a charged brush (charged by blowing with a dust blower, or stroking on vellum). It’s fast and simple, and does the job. Sending the camera away takes time and money and doesn’t always get the job done.

  • TedCrunch

    Quote: “Even today, any photographer (and videographer) who is worth his salt
    will prefer looking into the eyepiece than at an exposed display…”

    Try telling that to the makers of point and shoot cameras! Those infernal display screens have had their time. Now it’s time to go back to quality instead of ‘cheap.’

  • Will Mederski


  • Will Mederski

    yeah, i read a story about a soldier that created a rifle mount for his DSLR.
    and there have actually been some camcorders that took on this shape, like the classic Super8s.

  • MI Photographer

    Next time you fly, just cruise through security holding this thing by its handle.

  • MI photographer

    After shooting film SLR for years back in the 80s/90s, then seeing how digital came around and evolved, I find it surprising that the industry stuck with the film speed concept. I remember envisioning a system with a sensor that did not have “steps” per se with a trade off if you wanted more sensitivity.

  • E

    As long as aperture and shutter speeds follow fixed steps it makes sense to let the third corner in the exposure triangle do so too..

  • Rob S

    Im not sure but I think some auto settings allow 1 increment variations in ISO and shutter speed. Even if they dont when you have 1/3 stop settings for speed, ISO and aperture its pretty close with 27 steps in each f stop.

  • Eugene Chok

    useless in the dark… time to get some faster glass

  • Jeremiah

    What, like f/1.4? Or maybe f/1.2? Yeah, i got that. Still, dark is dark – and the sensor can gain up and show you things your naked eye cannot see.

    I guess i also should have disclaimed that i use manual focus lenses, so nailing focus through the eyepiece (on a 7D) is difficult anyway even in optimal light.

  • mokleTkcuF

    A static charged brush wont always get particles off a sensor but yes it’s a sensible first approach.

  • kjb

    yup, haven’t been any changes to the design of automobiles in the last 100 years!

  • Zos Xavius

    And so is the price!!

  • Dominic DeSantis

    Not sur why the author has such significant sensor cleaning uses. Make sure to power down you camera when changing lenses. A charged sensor can attack dust and when its fully exposed to the environment during a lens change it has more dust to attract.

  • dusanmal

    Film SLR cameras didn’t become of the size and shape as they were randomly. Need to hold and wind film was there but the main ingredient, including the “win” of the 35mm film size was in ergonomy vs. needs optimization. There were cameras of boxy or sleek designs even with film. They lost.
    While article focuses on the prism and viewfinder, other elements (size and shape; image/sensor size and related lenses qualities,…) are crucial. So, I welcome manufacturers to remove “old tech” mirror and prism but not for futile exercise in size shrinkage (drifting on topic: I rented recently Nikon D7000, wonderful camera by abilities… but way too small for my comfort, needlessly small). Determine size by ergonomic needs and lenses and if space is left after removing the mirror – put some NEW content in. Something new that digital imaging can profit from and something that we didn’t even dream of in the film days.
    Tech changes, ergonomy persists…

  • Brian

    You lost me with that “never clean a sensor by hand” ultimatum garbage. I hope the remainder of your article was more well-informed.

    Hand-cleaning sensors carries an inherently higher risk of sensor damage because you’re actually touching it. Some people try it and turn their cameras into paperweights. I get that. But it can easily be done correctly over and over with a little bit of homework. I have a 20D I’ve hand-cleaned for nine years and have yet to see any signs of damage.

  • Ken Elliott

    My experience is different. I shoot Nikon D700 and D800 bodies, and use a Nikon V1 with a EVF. In very low light, the optical viewfinders are much better. EVF is quite good until you hit a light level that caused the sensor to have difficulty.

    BTW – the D700/D800 AF is extremely good in low light. The Canon’s could not lock focus and were worthless in low light. By any chance are you shooting a Canon 5D or 5D MkII? (the MkIII is much better).

  • Ken Elliott

    Depends on the camera. With a mechanical shutter (D800), the sensor is covered during the lens change. This is not the case with my Nikon V1. Sadly, the on/off cycle is quite slow, so I don’t bother turning it off when I change lenses.

  • Jeremiah

    Hey Ken, just saw your reply. As i said, i have a Canon 7D and own only manual lenses, so that definitely shapes my opinion. Very little autofocus experience with it. The 7D optical viewfinder is not optimized for manual focusing, regardless of how much light there is. I’m aware the 5D models have great low light performance, but the 7D is not too shabby in terms of amplifying available light (even if it turns out very noisy).

  • Dr Simon

    “This one might seem like a minor point, but not having a mirror in front of the sensor really leaves your sensor exposed to debris and dust. I clean my camera’s sensors (with the menu option, of course. NEVER clean a sensor by hand) each time I use them on the field, and, most of the time, the mirrorless camera is the one that needs servicing because of the sheer amount of dust that gets stuck on the exposed sensor. This is something that will never change.”

    That’s simply not true. The reason that DSLR cameras get dust on the sensor is because of the action of the mirror circulating air/dust around the mirror box. The mirror does not prevent dust but actually makes the problem worse.

    Dust only sticks to the sensor when the sensor is charged. In a DSLR, air is moving in the mirror box as the sensor is charged and the shutter is opening, any dust that lands on the sensor at this time will stick (and most times will fall off when the in-camera sensor cleaning is activated). In a CSC (or mirrorless camera) there is no air moving as the shutter opens meaning it is less likely that dust will find it’s way onto the sensor when it is charged. When you change lenses on a CSC (and the camera is turned off as it should be) the sensor is not charged, so any dust that finds it’s way in will not stick. Also, mirrorless cameras tend to have their low-pass filter (or possibly another glass filter) set further away from the surface of the sensor so any dust that does land on it will be out of focus and not noticeable on the image.

    I know this as I clean cameras as part of my job and I almost never get CSC’s in for cleaning despite having thousands of customers who are using Olympus OM-D series, Fuji X series, Panasonic G series and Sony NEX series cameras.

    Also, saying you should never clean a sensor by hand is also untrue. There are many methods of cleaning a camera sensor and not all of them use fluid. A simple hand squeeze rocket blower will be more effective than the in-camera cleaning operation and presents no risk at all of damaging the camera.
    There is a small risk when using sensor swabs and fluid, but provided you are careful and follow instructions it is not a difficult job. It is actually quite difficult to damage a sensor, I have seen maybe 3 or 4 cameras in over 12 years that have had sensor damage due to improper cleaning.

    It is also worth noting that the in-camera cleaning mode is totally ineffective against oil or condensation marks which are noticeable in images shot at very small apertures.