Digital Photography from 20,000 Feet
by Wesley Fink on September 25, 2006 12:05 AM EST- Posted in
- Digital Camera
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.
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.
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.
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silver - Tuesday, September 26, 2006 - link
No Adaptall for digital cameras ?tsapiano - Wednesday, September 27, 2006 - link
Well, most DSLRs use the same lens mount as their film-based predecessors so you can use things like Adaptall on the new cameras as well if you really want. The problem with that is that this technique was pretty much abandoned a while ago, so to do this you'd be stuck using old aftermarket lenses. While it was relatively easy to make a universally adaptable lens when everyone was using simple mechanical couplings - the electronic communication used in modern lenses has made that much more complicated. As such, most modern aftermarket lenses are now generally built and sold specifically for the mount you are using.With that said, there are simple adapters that you can buy to mount Nikon, Leica, Contax, Olympus OM and Pentax lenses on Canon EF bodies. As the Canon mount has a smaller register (ie the mount is closer to the film plane) and wider opening than all of those mounts, it makes it possible to fit an adapter in there. The catch-22, however, is that these are very simple adapters and don't do much other than mechanically attach the lens to the camera - you loose aides like autofocus, aperture must be set on the lens (ie A or M exposure modes only), you're forced to revert to stop down metering, etc. As such, while this may be useful to use a special purpose lens or two it's not really what you want to do for your everyday photography ;)
Resh - Tuesday, September 26, 2006 - link
Nope.Wesley Fink - Monday, September 25, 2006 - link
No, Canon lenses fit Canon only, and same with Nikon. Each brand will only fit their own lenses and independent lenses made for that clens mount. Samsung licensed their lenses from Pentax and they will fit Samsung and Pentax. Sony bought Minolta so Sony and Minolta lenses both fit.nigham - Monday, September 25, 2006 - link
I'm really happy that AT is getting to digital SLR camera reviews. This article was slightly disappointing. As has been pointed out, anyone who doesn't know his or her f-stops and shutter speeds should certainly not be spending money on a Digital SLR just yet. My experience with my prosumer Canon S2IS says that it takes a while to _really_ appreciate these settings and they're not simply learned theoretically. And I don't particularly care for history, but maybe thats just me.That said, it's OK since I've only seen one real good DSLR introduction for beginners (http://www.firingsquad.com/hardware/panasonic_lumi...">here), and what matters most are the reviews, which I'm hoping will measure up to the usual AT standard. Here's what I'd like:
- Feature description and (in prose) comparisons to comparable and current cameras. What's really improved, and what's just marketing? etc.
- How good the documentation is. This is something woefully ignored by many camera review sites.
- Reference testing with a high-quality lens; since I would expect to be buying lenses eventually if I get a DSLR
- A section (maybe short) evaluating the quality of the in-kit lenses
- Battery tests (these are important! unlike that startup times in which case I totally agree with you). Also options for backup batteries (how expensive, availability)
- A (necessarily subjective) description of the "feel" of the camera output in various real-world scenarios like landscape, low-light, fast-motion etc.
- A human-readable description of how easy/difficult the UI is. I do not want a list of menu options five levels deep and 20 EVF screenshots, I need you to take a call and let me know what the bottom line is. How hard is it to change the basic stuff (F-stop, ISO, WB?); are there any customizations available; are there any quirks like controls that inadvertently get messed around with; does it have a on-screen histogram?
- How good the AUTO mode is, and when it fails. Personally, I believe that the primary job of a photographer is to see the photo and compose it. I'd like to know when I can afford to go auto and spend more time composing my shot, and when I can't do that.
- A set of sample photos in real-world situations
I think it would be nice to remember that even for hard-core computer enthusiasts, photography remains an art and is not easily described; and is nearly impossible to describe with numbers alone.
Lastly, I'd really appreciate an article on RAW workflow - if possible one that includes a discussion of the ways Linux handles DSLRs. That is something that changes quite a bit for users transitioning to DLSRs.
Resh - Monday, September 25, 2006 - link
Sorry, just can't agree with that. How can the inter-related tasks of exposure, choosing focus point, and depth of field be separated from composition?
mostlyprudent - Monday, September 25, 2006 - link
One thing I forgot in my earlier post (and forgive me if it has already been mentioned), I would like to see more on lenses. I think AT should test both the Kit lense and a high quality reference lense. I wouldlike to know both how good the camera can be with a great lense and how good of a value the kit lense offers.Thanks.
Resh - Monday, September 25, 2006 - link
I thought it was a good primer for beginners and was full of useful history, but couldn't shake the feeling that AT was trying to crowd into an already crowded room.While I fully agree with those who have pointed-out that a diversity of reviews is a good thing, I think that diversity already exists with sites like Steve's Digicams, DPReview, etc. In addition to those we have more art, in-the-field sites like Luminous Landscape that focus on how a product performs in the field.
Some have argued that AT should do reviews to the level of detail/bench-marking that is employed for motherboard and video cards. Here, I have a harder time as I don't see an SLR body as being comparable to those components.
AT reviews those parts in the context of choosing one to fit into a larger computer system. Alternatively, an entire system (e.g., Alienware) is tested against a home-built system with similar specs or at similar cost. This model, however, doesn't appear relevant to the SLR market as one cannot individually buy the processor, sensor, body, etc. that is the best and construct their own camera. Rather, a first time buyer chooses an entry point into a given manufacturer's "system" based on the body's attributes; lens cost, availability, and quality; and available accessories. For someone upgrading their SLR, the choices are even less driven the details that AT would likely be assessing. Rather, they'd be considering the costs of switching systems (e.g., from Canon to Nikon), or simply considering the value of upgrading to the latest and greatest, a question that existing sites can answer just fine.
All that to say that there are areas where current sites fail and where AT's expertise might be better leveraged. The main example, for me, is in the area of displays and printers. With regard to the former, quality CRTs are gone and LCDs present a purchaser with huge variability in cost, performance, and quality. AT could look at the display market from the photographer's point of view (appropriate brightness coupled with stable contrast, wide-colour gamut, ease of calibration, wide viewing angles, etc). This could be supplemented with discussion of colour calibration products. Similarly for printers, there is little to be found on-line that offers critical comparison of competing printers on different papers. Both of these areas would fit well within AT's current review framework.
Lastly, AT, while not a software site, could elevate the standards of software reviews by taking a hard look at the effects of different RAW converters, enlargement software, sharpening tools, and noise reduction software. I have not seen anyone do this in an objective, scientific manner.
AT is a fantastic site and while I applaud your willingness to branch-out, I am cautious about your getting too far from your core audience and your core strengths.
N
s12033722 - Monday, September 25, 2006 - link
It would be good to delve into the nature of how image sensors work and the differences between types of sensors. I think Anandtech would be an excellent place to discuss these aspects of the cameras.Image sensors basically work by photons interacting with light-sensitive portions of the sensor to create electrical charge. The efficiency of the sensor at converting photons into electrons is reffered to as quantum efficiency, and has a serious impact on how well a camera will perform under different imaging conditions. After the charge is collected, in the case of a CCD sensor, the charge is read out of the sensor, passed through a processing chain, and then digitized. It is important to note that this is an ANALOG process until the point of digitization. In the case of a CMOS sensor, the digitization may occur at each pixel on the sensor, at the end of each row or column of pixels on the sensor, or off sensor like the CCD. Each approach has advantages and disadvantages, generally trading off noise performance for pixel size.
Image sensors are characterized by a number of factors. Noise, dynamic range, pixel size, and so forth tend to be interrelated. The comment in the article about dynamic range was somewhat simplistic. Dynamic range is primarily governed by the charge capacity of the pixel. A sensor will be characterized by a quantum efficiency as noted above, which means that as more photons strike the sensor, a greater charge will be built up. If a very bright spot exists on the image, that spot will usually fully charge the pixels under that spot, limiting the output at that level. For instance, let's say a pixel has a full-well charge capacity of 30,000 electrons, and that there is no noise. The dimmest pixel possible on the image would be 1 electron (well, 0, but let's say 1) and the brightest would be 30,000, for a dynamic range of 30,000 to 1. Now, in reality there are noise sources in a sensor. Many of them. That will typically mean that the dimmest pixel will have a charge on it, which reduces the dynamic range. Perhaps there are 500 electrons of noise. Now the sensor has a dynamic range of 30,000 to 500 or 60 to 1. Far less. The ways to increase dynamic range are to decrease noise or to increase charge capacity. Unfortunately, charge capacity is directly tied to the physical size of the pixel, so as resolutions get higher, pixel size gets smaller, and dynamic range suffers. It is entirely possible to build sensors with dynamic ranges that meet or exceed those of film, but generally not within the size constraints imposed by sensor size and the perception of resolution as king by most consumers. When was the last time you saw the dynamic range or noise performance advertised on a camera? Even though these are arguably far more important than resolution to most SLR purchasers, these details are glossed over.
I would like to see a basic overview of the guts of a digital camera given. Sensors, data conversion, data processing, autofocus mechanisms, etc. Anandtech seems like a good site to do it. Contact me if you need help or technical details.
Curt - Monday, September 25, 2006 - link
Could you include in your reviews astronomy photos? As an amateur astronomer, I'd be interested in comparing the very low light sensitivy and contrast ratios of the CCD's.Thanks in advance