Lenses on Digital SLR Cameras

While digital point-and-shoot makers normally quote their lenses in familiar 35mm terms, no such convention exists in the digital SLR market. Here, everything is the opposite, as all specs are defined in 35mm terms even though the digital SLRs themselves use a smaller APS C size sensor. This is even carried so far as using 35mm equivalents to define lenses designed for the Digital SLR - even though the "digital-design" lenses can't even cover the frame on a full-size 35mm camera. Thus lenses like the common 18-55mm Canon and Pentax kit zooms and the 18-70mm Nikon and Sony (Minolta) kit zooms really describe those lenses as if they were 35mm.

To know what a lens can do on a digital SLR you have to know the lens factor. Nikon, Pentax, Sony, Minolta, Samsung (Sony sensor) and most others use a sensor about 23.6 x 15.8mm with a lens factor of 1.5. This means that if you multiply the stated lens focal length by 1.5 you will get a focal length of how that lens behaves on your Digital SLR. Let's see how that translates.

SLR Lens Factor Conversions
35mm Focal Length 1.5 Lens Factor
Nikon, Pentax,
Sony, Minolta,
Samsung
1.6 Lens Factor
Canon
2.0 Lens Factor
Olympus
10-20mm 15-30mm 16-32mm 20-40mm
14-45mm 21-68mm 22-72mm 28-90mm
18-55mm 27-83mm 29-88mm 36-110mm
18-70mm 27-105mm 29-112mm 36-140mm
24 mm 36 mm 38 mm 48mm
28 mm 42 mm 45 mm 56mm
35 mm 53 mm 56mm 70mm
50 mm 75 mm 80 mm 100mm
85 mm 128 mm 136 mm 170 mm
70-210mm 105-315mm 112-336mm 140-420mm
135 mm 203 mm 216 mm 270 mm
75-300mm 113-450mm 120-480mm 150-600mm
500 mm 750 mm 800 mm 1000 mm

Canon uses a CMOS sensor that is slightly smaller at 22.1x14.8mm, and therefore requires a slightly higher 1.6 lens factor. This makes a slight difference in the real focal length of the lens on a digital SLR, but both 1.5 and 1.6 factors are close in value.

Olympus has taken a totally different approach to the sensor used in their digital SLR cameras and has adopted a new digital-only lens mount and lens system called the four thirds system. There is a consortium of 4/3 members that support the 4/3 standard. They include Kodak, Fujifilm, Leica, Panasonic, Olympus, Sanyo, and Sigma. Olympus introduced the first 4/3 system camera and lenses in 2003. Panasonic recently added their own 4/3 camera in the Lumix L1, along with several Leica 4/3 lenses.

It should also be mentioned that Canon has introduced a professional and a premium grade full-frame digital SLRs. There is no lens factor required for these SLRs with a 35mm-size CMOS sensor. These two cameras are, however, in a different category, with the EOS 1DS Mark II selling for about $8000 and the newer EOS 5D for about $3300. Nikon, another recognized top pro brand, has stayed with the DX/APS size sensor in their top pro camera, the Nikon D2X.

Technology has certainly reached the point where 35mm size sensors could be manufactured for a relatively reasonable cost; however, there is no clear movement at the present time to a 35mm size sensor. Most in the industry seem content with the APS C to DX size digital sensor. Perhaps in the near future, we may see some movement to full-frame sensor for the top Pro cameras with APS C/DX for mainstream SLRs. It's just a bit too early to do anything but speculate at this point.

Lens Angle of View

Now that you have a good idea of how to figure out lenses on digital SLR cameras, it is worthwhile to remember why we change lenses.


Wide angle, normal and telephoto lenses see different points of view as you can clearly see in this same scene taken with 35mm, 70mm, and 105mm lenses on 35mm film. From the chart above you can see this would be equivalent to 23mm, 47mm, and 70mm lenses designed for 35mm photography and shot on a Nikon or Sony (1.5 factor) digital SLR. This is a very important distinction and critical to understanding how 35mm lenses behave on today's digital SLR cameras. A 28mm lens designed for a 35mm camera "sees" as if it is a normal lens on a digital SLR, a 50mm normal lens "sees" like a 75mm short telephoto (portrait) lens on a digital SLR. Zoom lenses have been around for quite a while now and most will be familiar with the different view captured with each type of lens. However, they may be surprised to find that the 28mm-80mm wide-angle to short telephoto kit lens they bought for 35mm "sees" like a normal to medium telephoto 42mm-120mm lens on the digital SLR. That is why the new kit lenses that sound so exotic like the 18-55mm and 18-70mm are nothing more than the APS C size version of the old reliable 28-80 and 28-105.

Once you get accustomed to the new focal length definitions for digital SLR cameras, things will fall into place. The shorter the focal length the more extreme the wide angle and the larger the "view" included in the image. The larger the focal length value the more "magnified" the image. Wide angle ranges are very useful for interiors and shots of groups of people. Telephotos are great for shooting from an audience or nature photography like birds. Normal of course is a good all-around focal length.

Because existing 35mm lenses make up the bulk of available lenses on digital SLR cameras, and because the real lens value is a multiple of 1.5 or 1.6, it is easy to see that wide-angle lenses are hard to find on digital SLRs. The 35 wideangle 28mm is a normal lens on a digital SLR, and the super-wides usually stop at specialty fisheye lenses around 15mm, which is still a normal wide 23 to 24mm on digital SLR cameras. As a result, almost any extreme wide-angle lenses you will find for digital SLR cameras will be designed just for digital cameras. These include the Sigma and Tamron lenses in the 10-20mm range, and lenses from the major lens makers like the Nikon 11-18mm.


The Olympus four thirds system lens factor is included mostly for reference, since Olympus manufactures a whole new lens line for their digital SLR. None of the older Olympus lenses from 35mm work on the new digital cameras unless you use a special converter. Even with the converter they will work in full manual mode only. The 2.0 lens factor does come into play for third-party lenses designed to work on the Olympus 4/3 cameras, so you can determine the effective focal lengths with the 2.0 multiplier. However, independent lens makers are mainly designing for a 1.5 to 1.6 lens factor, and the 4/3 equivalents are not always very attractive. Sigma markets basic and specialized fast digital lenses in the 18-55mm range. That's a desirable 27/29 to 83/88 on a 1.5 or 1.6 camera. However, on Olympus 4/3 that is a 36-100mm lens. That is still useful, but there is almost no wide-angle when mounted on a 4/3 camera. This is the problem Olympus faces. Until others adopt this open standard four thirds mount, the only lenses designed specifically for the 4/3 system will come from Olympus.

It should now be clear why the digital SLR, with the ability to see through the taking lens, is a more flexible platform for digital photography. Today's Digital SLRs focus and meter exposure through that same taking lens. With auto-exposure and autofocus, a digital SLR can be as simple as any point-and-shoot camera. Plus there is the added flexibility of a much larger selection of interchangeable lenses that are available to allow the user the best chance to capture what they want in any situation. However, despite the fact you don't need to know anything about F-stops, shutter speed, and the light sensitivity of the sensor, we will tell you with absolute certainty that you will take better images if you do understand a bit about what is going on behind those automatic functions.

Understanding 35mm and Digital Lenses Photo Basics: Painting with Light
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  • Sunrise089 - Monday, September 25, 2006 - link

    Wesley - I feel that wgoldfarb makes one very good comment which I may have missed your answer to. He states that if you have decided to take a less technial approach to digital camera reviews compared to your other hardware reviews, and the other editors are suggesting even less technical detail than this article had (shame on you Anand, Derrick, etc, I read many articles by you guys that forced me to do outside research, and it made me a more informed user because of it) then why are you focusing on the higher-end digital camera segment, where the buyers will tend to be much more informed. The only reasons I can see are:

    1) This is the segment more personally interesting to you, so you're going to cover it
    2) This is the segment where the most new products are appearing, so you will have the most to review
    3) This is the segment that still opperates at high margins, so more samples will be sent to you to be reviewed and more inside information will be directed your way
    4) You have decided to attract the same users who buy DellXPS and Alienware systems - users that have the $$$ to afford a high-end product, but lack the motivation to become an informed consumer, and will therefore buy whatever products they happen to be told to buy.

    Options 1,2, and 3 will still attract a more informed consumer who desires technical detail, and by denying them that you are in effect offering reviews of one class of product written in a style for an entirely different class.

    Option 4 has never been AT's approach, and furthermore, the "more money than brains" class probably won't seek out any product reviews anyways, prefering to simply buy the more expensive version of the camera their coworker has recently been showing off.
  • Wesley Fink - Monday, September 25, 2006 - link

    There is a misunderstanding here. I did not mean a lower degree of technical expertise, I meant a different way of approaching digital camera reviews. Sites like dpreview do an excellent job at what they do, as many point out here. We hope to bring a different and a bit unique approach to these reviews, and not just try to emulate other sites.

    As for #3, I confess I have personally bought the stuff I will be reviewing so far, a Sony and a Nikon D80, so that kills that argument :) #4 doesn't even deserve comment, it is not my style or Anand's, though we are all too often ready to condemn mass market computers without truly looking first.

    What some of you are forgetting here is there is a great void between sites that eat, breathe and live digital cameras and many of our readers who really want some solid info on digital cameras, but who find some of the super technical sites less than approachable. These readers want solid info to help them buy what they need, but they have not yet reached the level of photo knowledge where they are ready to argue "exposing to the right" makes digital photography different from film photography. It's a valid point, and I get what "exposing to the right" means from the link to Luminous Landscape, but I think it will be a while before that perspective is a major part of our Digital Camera reviews.

    I have received a huge number of emails with very good suggestions for Digital Camera testing, and we do appreciate your comments. We can't do it all, but we are very interested in what you have to say.

    As an aside Derek is busy with his wife in the hospital having their first baby and Anand is now in San Francisco covering IDF.
  • wgoldfarb - Monday, September 25, 2006 - link

    quote:

    As for your experience with the sensor in your camera, it appears to be camera/sensor specific. I could make the same argument for every film that exists - they all respond best to certain exposure techniques and those techniques differ depending on the film. However my personal experience has been the opposite of yours - blown highlight from overexposure are much more an issue than underexposure in digital, since I can usually correct shadow detail in Photoshop and I can't always recover blown highlights.


    The issue I was referring to depends on the linear nature of digital sensors, and AFAIK is common to all digital cameras. A full discussion probably does not belong here, but let me try to briefly explain what I meant.

    Digital camera sensors are linear devices, whereas we perceive light exponentially. This creates a mismatch between how sensors record an image and how we perceive it, to the point that about half of the perceivable tonal values in an image are recorded in the brightest f-stop of dynamic range of a camera (a typical camera may have about 5 f-stops of dynamic range). Thus, the ideal exposure for a digital sensor is one where the histogram is as far to the right as possible, yet without reaching the point of blown highlights.

    I probably did a terrible job of explaining myself in a single paragraph, so a much better explanation http://www.luminous-landscape.com/tutorials/expose...">can be found here.
  • wgoldfarb - Monday, September 25, 2006 - link

    I understand your problem of trying to meet everyone's needs. But I will try to continue to convince you to go more in the direction I'd like to see (can't blame me, can you? ;-)

    quote:

    Our real issue with Digital Cameras is knowing which audience to address. We do understand there are readers that are vey knowledgable in digital photography, but there are also readers who know next to nothing about digital cameras.


    and

    quote:

    I would also bet you that the great majority of our readers who use digital cameras generally use auto - even with SLRs - and only once in a while go off the program for special situations.


    Points very well taken. Still, limiting your reviews to more "basic" skill levels may be a disservice even to those users with basic skills. Cameras chosen based on "basic" knowledge may serve readers well intially, but as they start to learn more (by reading your guides!) they may realize they made a wrong decision because they did not know enough. The problem is, these cameras are expensive, so it is not easy to upgrade them as your knowledge and skills improve. Ideally, you should choose a camera that can fit your current skills, but also those skills you will learn once you start experimenting with your new camera, as well as the many ways in which you might use the camera in the future. Before selecting components for a new rig people here usually determine how they will use their new build: will they overclock? is it for gaming? Same thing for a camera. If I know I will only use my camera in Auto mode for casual family events, I will probably choose a very different camera than if I think I may eventually try some more advanced settings or different types of photography. But if I don't know anything about those advanced modes I will be unable to make that decision.

    An approach that may work is to use different instruments for different people. Readers who "know next to nothing" might benefit more from a number of "guides" to teach them the basics of what they need to know about digital cameras to make a better purchase decision, and to eventually benefit from more thorough reviews. These guides could also help them decide how they will use their camera in the future. Thus, you could have a number of introductory guides for newbies, allowing them to learn the jargon and the basics they need to understand your reviews and make a good purchase decision. If you add AT's outstanding community support, this should be enough for almost any level of knowledge. This is precisely how I started learning about computer hardware. I read lots of beginner's guides (like those to be found in many stickies in AT's forums) and made extensive visits to your forums until I knew enough to understand your reviews and decide what features were important for my needs. If people do that amount of research for GPUs costing $300, they will probably also do it for camera systems costing up to $1000.

    Yet another approach that may work is to tailor the review to the camera's market. If you are reviewing an entry level SLR you may serve that camera's audience quite well with a more limited review. Yet, when you review cameras aimed at higher segments of the market, you may conduct more thorough reviews to benefit the more knowledgeable likely buyers of these cameras. Also, having this "advanced" content will allow your beginner users to learn more, and help them push their skills to the next level where they may stop relying on their camera's Auto setting so often.

    Don't get me wrong, I do realize the problem you face. But I honestly believe you can add a lot more to the current mix of review sites by doing what you do best: reliable, thorough, in depth reviews.

    quote:

    AT is known as a computer equipment review site, so if we sometimes go too far on the technical side of computer testing it is normally forgiven


    Agreed. It is not only forgiven, it is even expected. But what is stopping you from also becoming known as a digital SLR review site? ;-) If you apply the same "business model", the same standards and techniques to SLRs that have made you so successful in computer hardware, I am confident you will enjoy the same level of success in the area of digital photography.

  • Belldandy - Monday, September 25, 2006 - link

    I like your introduction to digital SLR's, well written and covers much of the basics. Others have commented that dpreview is the premier site for photography, which they are very good at, but 2nd or 3rd opinions are always a good thing. Even the pro's may miss out on some details. Detail wise, I believe readers of Anandtech who are interested in digital SLR reviews, will have fairly basic understanding of photographic basics. Certainly maybe not everyone will know the technical differences behind say lens based or sensor based image stabilization, or image quality and noise of different sensor size, sensor type, and say software processing at different ISO. But in depth highly technical reviews is what makes anandtech articles so intriguing and there is bound to be new stuff for all of us to learn.

    Personally I'm a photo enthusiast using a Fujifilm S3Pro & and Nikon F90x film SLR. It's a slow camera compared to other DSLRs, and perhaps my F90x. The power on time, shutter lag and focus times are all very good, (using my set of Sigma F2.8 zooms at least) however the buffer size for raw images and flush rate to compact flash is painfully slow. My point is most equipment have their strengths / weaknesses and many reviews fail to stress that it is a very good jpeg camera, with high image quality. Have to at least comment on what it was designed for, and whether it's suitable for each individual. Speed alone won't make for better images, and if I needed more speed, switching to jpeg or xD type H cards or lower to standard dynamic range, all provide additional speed for the situation. So perhaps reviews should give pointers on how to bring out the best in each camera.

    In this area I totally agree with you on basing your reviews on the target group who will be interested in buying the said camera. Entry level DSLR cameras need to be tested from the basics up with both kit lens and reference for those moving up from point and shoot. Most of their targeted buyers are first time SLR users, some pro's may buy an entry level camera for backup use and rest of the family and some from film slr's. For more pro oriented bodies, more empahsis should be placed on image quality, noise, speed, and other technical details for the more advanced users.

    I'd like to see tests of cameras using identical images at different ISO's that we can compare across cameras and Brands, using both reference lens and kit lens as well. Speed of both camera focusing, power on & shutter lag and image processing are important. Viewfinder image quality and built in + external flash operation are significant areas that seperates SLR & Point and shoot experience. Hopefully those can be touched upon for indoor and fill flash shots.
  • gohepcat - Monday, September 25, 2006 - link

    Good stuff. I'd like to pass on some wisdom I learned a long time ago about photography and I like you to look into it a little more.

    10 years ago I was turned on to a photographer named Fred Picker. I was never really into his work, but his books and newsletter were outstanding. He was a crotchety old man, but he was a real straight shooter.

    One of the things I remember him talking about were lenses. He basically said...forget about lenses. You blur your picture far more by handholding your camera than any small imperfection in your lenses. Also the act of the mirror slamming against the top of the camera causes shake that is larger than the resolution that the lens can provide.

    I love the digital age, and don't fight it one bit, but I'm sad to see some of the qualities of film disappearing. You still can't really make a digital image as good as my $100 sixty year old Rolliflex with Tri-X pan (a 60 year old film)

    Tonal range is HUGE, and I hope things improve in that area.
  • silver - Monday, September 25, 2006 - link

    Excellent ! A good, solid primer capturing some of the basic developments, capabilities and challenges of digital imaging.

    I'd like to make a couple of points of course and given some of the previous commentary I'll provide a little background on myself. I used to have a photography studio and I'm still often asked to photograph portraits, weddings and such. I currently work for Really Big Computer Co. in a technical role and I still shoot film even though I have a Fuji FinePix S602 digi-cam.

    First, if I were a pro again I'd be shooting digital in a heartbeat. It's cheap, fast and easy. The results are instantly gratifying and lead to increasd sales. Boy are there a lot of analogies there ! That said I'm not a pro and I only shoot digital as A) a replacement for Polaroids and B) for use in a digital realm such as website design.

    Second, "Image stabilization was first introduced by Nikon and Canon in specialized zoom lenses. These zoom lenses were first designed for pros at pro prices". Wasn't it the longer high magnification lenses such as the Canon EF 300mm f/2.8L IS which is extremely popular with sports photographers that first received stabilization ? And of course I realize that the majority of your readers would no more know the difference between a telephoto and prime lenses than they would between Jimmy Carter and Dubya.

    Third, "Digital Challenges: What Needs to be Improved". I think you left out resolution ;>) Digital has certainly come a long way however the actual image resolution still pales when compared to any good film/camera combination.

    Fourth, unfortunately you didn't directly mention the other formats of film. When it comes down to it most pro's never bothered with 35mm as it faced the same constraints as does digital which is to say that there is a limit to the amount of visual information that can be acquired per each square millimeter of light sensitive medium. That's why most of us "old timers" used cameras like the RB67 which has a film area that is several times larger than 35mm's dinky 24X36 window. 35mm was deemed adequate for low end weddings, sports, stock and wildlife photography but it was widely recognized that the limitations in image quality was difficult to overcome. Only a few photographers such as Sebastio Selgado, W.E. Smith and H. Cartier-Bresson chose the 35mm format while those that wanted the better tonal scale used medium format cameras such as the Hasselblad's, Mamiya's, Pentax, etc. or even larger cameras such as the 4X5's, 5X7's (still my favorite), the 8X10's and even larger cameras.

    I would hope that you touch on the issues of image modification, output ("printing") methods and archival storage. When faced by the "technoratti" I like to paraphrase Lance Armstong and say "It's not about the camera" so in turn I hope that your scope goes well beyond the capturing equipment. In particular image stability which is one of the most poorly illustrated facets of digital imaging, and image archiving which is a huge concern given the extremely limited lifespan of digital files and formats.
  • Wesley Fink - Monday, September 25, 2006 - link

    Thanks for your comments. The best information I could find indicates you are correct that the first image stabilized lenses were designed for the long fast primes. It really doesn't matter for our discussion in the article, but in the interest of historical accuracy I have updated the two sentences on p. 10. They now read "Image stabilization was first introduced by Nikon and Canon in specialized lenses designed for action photography. These lenses were first designed for pros at pro prices, but image stabilization quickly found its way to consumer zoom lenses."

    As for medium and large format film, I confess I also shot 120/220 when I was selling my images. Things have improved a great deal, but the larger negative still has advantages. I did list these formats in some of the photo charts, but I felt it would just lengthen the article if I spent any time on the large foramts. It is something those shopping for a digital SLR would not likely care much about, although the digital backs for the medium format cameras are incredibly interesting.

    We will definitley consider your suggestions as we move forward in Digital Camera reviews.
  • silver - Monday, September 25, 2006 - link

    LOL ! I spoke with Fred on several occassions. The last time was immediately prior to him selling Zone VI to Calumet when I bought one of his last cherry wood 4X5's. You had to take Fred with a big grain of salt. He was a shrewd businessman and realized that most photographers wanted "straight talk" instead of scientific facts.

    I agree about the digital revolution. It's certainly an exciting time. I subscribe to the alt-photo list (http://www.usask.ca/lists/alt-photo-process/)">http://www.usask.ca/lists/alt-photo-process/) where many photographers are combining the capabilities of platinum printing with digital negatives created using inkjet printers. It's all about the image and permenance.

    Still, I'll keep shooting film for as long as possible. No hard drive crash is going to ever take out my files again and I can always scan negatives which don't take a computer to look at or batteries to run. Hmmm, kinda like that Rollei of yours !
  • Wesley Fink - Monday, September 25, 2006 - link

    Storing images on a DVD certainly appears more "crash-proof". I don't recall seeing archive times for DVDs, but I do know know corporations who store GMP (Good Manufacturing Practices) records on optical, and those must have a minimum 100-year storage life.

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