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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wheel - Tuesday, September 26, 2006 - link
Thanks for your reply.Regarding the Canon 50mm 1.8, I think most people would agree that the 1.4 is better since it has full time manual focus and also a silent USM motor, plus 8 aperture blades instead of 5 for nicer, smoother looking bokeh (out of focus areas in an image). Of course when you consider the cost differential most people choose the f1.8 and for many it is the smarter choice! However I still believe your sentence in the article suggesting that it happens to be the sharpest lens in the lineup a little misleading. Not a big deal I guess.
If I can make some comments on the following paragraph:
There are plenty of Digital Camera Review sites out on the web, so you may ask why AnandTech is re-launching a Digital Photography section. It appears that current sites are rarely on target with what computer enthusiasts want to know about digital cameras. Some sites make the assumption that the reader knows a lot more about photography than our average reader, which often leads to much of the review being gibberish to a non-photographer. Other sites dwell on tests of things like "start-up times" that were important in early digital, but have become all but meaningless in today's digital SLR market. Still other sites, which are very well-grounded in traditional photography show an obvious lack of knowledge about computers and computer tools that make digital photography so flexible today. It is our sincere belief that we can do it in a better way for our readers and computer enthusiasts everywhere, but please help us as we try to reinvent this wheel. Some of our readers may not like AT delving into Digital Camera Reviews, and to them we say you just can't ignore digital photography any more. Today's digital imaging is nothing more than an optic stuck on a computer, and there is very little left of the mechanical gems that once ruled the world of photography.
A few points:
"Some sites make the assumption that the reader knows a lot more about photography than our average reader, which often leads to much of the review being gibberish to a non-photographer."
So a 'non-photographer' will find a technical review on the big digital camera sites gibberish? I don't think that is a problem, because such reviews aren't really aimed at non-photographers. I would guess that non-computer users are going to find articles on Anandtech about ram timings difficult to understand too!
Other sites dwell on tests of things like "start-up times" that were important in early digital, but have become all but meaningless in today's digital SLR market.
See my comments re: sports / action photography in my previous post. Start up times, shot to shot times and file flush times are quite important to me! Other sites have (very comprehensive) standardised tests that include these timings. I wouldn't say they dwell on the subject though, unless a particular camera is unusually bad at it. If it is not something that is relevant then a reader can easily skip it.
Still other sites, which are very well-grounded in traditional photography show an obvious lack of knowledge about computers and computer tools that make digital photography so flexible today.
In my years of reading the major photo review websites, I haven't encountered this. Without asking you to be specific, can you mention general examples of what you mean?
Cheers,
Ian
tagej - Tuesday, September 26, 2006 - link
The reality is that most computer geeks (myself included) are not photography experts, but are overall tech-savy and interested in things like digital SLR cameras.Sure, I can go to sites like dpreview and the like, and they do an excellent job of reviewing cameras from a pro or prosumer perspective. I could sit and read a bunch of stuff on those sites and educate myself to the point of becoming very knowledgable about cameras... Most of us don't want to do that, or we would have already done so. Instead, AT hit it right on the head with this article, it's a look at digital photograhpy for the tech savy who are not photography experts.
arswihart - Tuesday, September 26, 2006 - link
I totally agree with "wheel." If you feel the need to review cameras, go ahead, but thats not what I come to Anandtech for.aeternitas - Monday, September 25, 2006 - link
" The artistic types distrust turning their vision into cheap Adobe Photoshop tricks, and the tech-savvy are so enamored of technology and editing that they often don't have a clue about what makes a good photograph and what lens to use in a given situation. "I stopped reading there. If you want respectable people to respect you, its a good idea not to be a fucking jackass and insult the readers in the second paragraph. Get some common sence.
Resh - Tuesday, September 26, 2006 - link
Have to side with Wes on this one. Nothing in his words are offensive. He is simply stating the view point of two extremes of the population who both hold very valid positions.Wesley Fink - Monday, September 25, 2006 - link
These are comments from discussions I have had on Forums and in emails with readers. They were not meant to offend, but to point out the fact that the art and technical don't always mix well. This is particularly true when the market, and not the people affected, is forcing changes in the way people work.ksherman - Monday, September 25, 2006 - link
since we have had a camera review on AT! Kudos!To those that say no, I also like to read reviews from multiple sources. AT- dont try to be dpreview, make your reviews a little less technical, easier to understand. Not to fault them, but you need to have some pretty serious photography knolwedge to get their reviews. I would welcome an easier to understand set of reviews. (I do still enjoy reading about my level :-))
On another note, on the last page, you called canons new camera the Rebel XT1, its actually the XTi.
Also, take a gander at the Panasonic Lumix DMC-FZ50, its a sort of pre-digital SLR camera. It basically is a digital SLR, but with an attached lense. Its looking to be my next camera purchase since I am too poor to afford the "real" DSLRs.
saiku - Monday, September 25, 2006 - link
I am a hobbyist photographer (Canon 350D) who likes to do macros/scenery when I can. What I'd love to see are guides for people who want to get into DSLRs and don't know which camera system to buy into. For example, if a person is interested in macros, should he buy into a Nikon system? What about the guy who wants to shoot lots of indoor shots of his baby? Lens choices are very tough for newbies to make and a hefty dose of attention to what lens to pick would be great.PokerGuy - Monday, September 25, 2006 - link
Wes, thanks for the great article. I'm a grizzled vet when it comes to PC tech, but when it comes to photography I'm pretty much a noob. I appreciate the article and look forward to reviews, especially since I'm about to purchase my first digital SLR camera.One dumb question: are lenses for SLR cameras "standard" in terms of connecting to the camera body? ie, can I take a Canon EOS Rebel 2000 SLR lens and hook it up to some other digital SLR camera?
Resh - Monday, September 25, 2006 - link
Also, Canon EF-S lenses only fit certain cameras (Digital Rebels, 20D, 30D), but EF lenses work on all current Canon bodies, digital or film.Third party manufacturers like Tamron and Sigma will make lenses for both Canon and Nikon.