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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squiddy - Thursday, February 15, 2007 - link
I'm fairly versed in film and digital SLRs and have been shooting since the mid-80s. Nikon afficionado here but I did have a few Canon EOS film bodies back in the day. Currently use a D70s and soon hopefully a D200 in my bag.Anyway, as to sugestions for future reviews, the technical aspect tests are all well and good since numbers are always easy to quantify. The MP count, max resolution, test charts and etc do help people choose cameras after all. What I'd like to see more of are subjective reviews. How user-friendly is the camera? Are the menu's easy to navigate and the features easy to get to? How are the ergonomics and will my hand require a chiropractor after a long day of shooting? Is the camera balanced even when using a medium telephoto lens? How about accessories (flash kits, filters, battery grips, flash brackets, etc), are they useful for this camera or just gravy?
What made me write these additional questions is that I experienced it when I borrowed a Canon 350d for a friend's wedding. This was before my Nikon D70s and I absolutely loved/hated it. The pictures were great but required heavy menu navigation for white balance and iso settings. The camera was lighter than my old film Nikon so it wasn't tiring to carry all the time but the grip was awful. My pinky was sticking out under the body and a;; the weight was focused on the upper/rear quarter of my right palm. I'll tell you now, it hurts to use it for a long time. Especially with a 430ex flash. I then tried a friend's D50 and a D70 after that and it solidified my Nikon preference. Great ergonomics and the two dials give you much greater flexibility on the fly.
These reviews are probably aspects that the average consumer won't consider before purchasing and just focus on numbers but it greatly affects the usability of the camera in the long run.
Thanks guys and keep up the great work!
appu - Sunday, October 8, 2006 - link
I don't know if these have already been covered in the comments earlier. There are quite a few and I didn't read them all.1.) When talking about vibration reduction, you need to make sure you tell your readers that VR/IS *cannot* eliminate subject motion blur. It can only eliminate (to a degree) blur caused by handshake. I'm surprised you missed such an important point considering that you felt most AT readers are newbies at photography. It's all dandy to believe that VR gets you sharp images all the time. No, it doesn't. There are caveats and you might have mentioned them.
2.) The real benefit of SLR cameras is - more than anything else - the fact that the photographer sees what the lens sees. That's a major, major advantage of a SLR over point-and-shoots and rangefinders which exhibit parallax error by the nature of their design, especially if the subject is close to the lens/camera. Given this, you might have also mentioned that sensor-based stabilization techniques are a bit of a misfit (atleast that's what I tend to think) because having a stabilized sensor still *will not* give you a stabilized image in the viewfinder. However, lenses which have VR in-built *will* give you a stabilized image in your viewfinder - again going back to the "what you see is what you get" thing. Having stabilized sensors is good for the customers as they don't pay VR royalty on every lens they buy, but I don't see the point in seeing a shaky image in the viewfinder and somehow expecting something sharp (to what degree I may not know) in the final image. Maybe 99.9999% here (or anywhere) wouldn't agree with me on this point but I think it's worth a note.
3.) Not all kit lenses are dogs. The 18-70 DX I have for my Nikon D70 is a wonderfully sharp, contrasty lens (of course in available light situations) and after almost 2 years of shooting DSLRs I can safely admit that I've not "outgrown" this lens. It still manages to surprise me every once in a while and I don't see the need for an exotic f/2.8 zoom in this range as yet. Point I'm trying to make is - don't berate kit lenses. They are there for a reason, and as with any lens, there are certain advantages and certain disadvantages. As a photographer, it's important to understand what every bit of your equipment is good at and then maximize the technical potential of your images because of this understanding. Infact, building up on this point...
4.) I'll go so far as to say that, even with fixed focal length (prime) lenses, the so-called "sweet spot" in terms of image sharpness and contrast is usually achieved when the lens is stopped down by 1.5 to 2 stops from its maximum aperture. If you are always going to think in terms of how zoom lenses are "bad quality" compared to primes, I'd encourage you to start shooting 2 stops down on your primes (and thus lose all the speed advantage these primes offer). I think you get what I'm trying to say. Let's not get too hung up on trivialities like this because, and I repeat because, modern zooms, even the consumer zooms produce wonderful images in the hands of capable photographers. And then you have pro-grade zooms like the 70-200 f/2.8 VR from Nikon and Canon's 17-40 f/4L etc. Yes, they are costly, but so is a 300 f/2.8 VR Nikkor or a pro-grade ~100mm macro. The price differential is evident only when you start looking at wide-to-medium-tele or super-wide-to-normal fast zooms (28-70 f/2.8, 17-55 f/2.8) and even then the output from these lenses is well worth their cost and the walk-around convenience they present to photographers who prefer this range of focal lengths. So, not all zooms are "bad". Things have improved, just as they continuously do in the computer hardware business. Let's not get stuck in old notions based on old equipment manufactured using old processes.
Keep up the nice work!
appu - Sunday, October 8, 2006 - link
Ok, one last point -5.) In your second last page, you talk about "lens confusion" and how you'd like the industry to move to a standard naming of lenses. I don't understand what can be more standard than the focal length itself - a very physical property of a lens. A 35mm lens has a focal length of 35mm. Period. It doesn't depend on what format camera it's bolted on to. A 35mm lens is 35mm whether it's used on a 4x5 view camera or a 645 medium camera or a 35mm film camera or a digital equipped with an APS-C or.... you get the picture. In itself, the naming of the lens by its focal length (range, with zooms) is *not* confusing. What's confusing is what people make it out to be - quoting effective focal lengths for formats all and sundry, where as in reality, the measure everyone needs to be worried about is field-of-view. A 35mm lens will have different fields-of-view when used with different camera formats.
We don't need a standard for identifying lenses. We already have one - focal length (a physical property that doesn't change) and field-of-view (a very measurable metric). If anything, it's the "effective focal length" paradigm has to be done away with, IMHO.
appu - Sunday, October 8, 2006 - link
In the last line of the third from last paragraph - Nikon doesn't make a 11-18mm as far as I know. They do have a 12-24 f/4 DX and Sigma also has a 12-24 (I think a non-constant aperture) which can be used on full-frame cameras too, unlike the Nikon 12-24 DX. The 11-18mm is made by one (or both) of Tamron and Tokina I think.directed - Wednesday, September 27, 2006 - link
When reviewing DSLRs, I want to know how quickly they can autofocus in different lighting conditions. I want to know how good the autoexposure is in different situations. I want to know how the different flashes perform in different settings (not just the built in ones, but the ones you can buy for them). I want to know how accurate the color reproduction and contrast is. I want to know how good the jpg compression is (lets face it, few people will be using RAW). I want to know how long the batteries will last in different situations. I would also like there to be a comparison with other models in a similar price range as well as a comparison with the cheaper and more expensive models of the same manufacturer.Boy, looking at my post I sound demanding. LOL, I'm sure Anandtech is up to the challenge.
yyrkoon - Wednesday, November 1, 2006 - link
I dont know, I dont use AF for demanding lighting situations, I use the infinite Focus setting, and set the rest manually. That, and I think all 'prosumer' DSLRs have a fairly 'shitty' on cam flash, and alot of us would probably be more concerned with the hotshoe 'adapter'However, I will agree with battery life as an important factor, but to be honest I'm personally more concerned with how fast the camera is (FPS), and the media type used.
I see alot of stuff on dpreview.com like 'default <insert something relivent> setting is BAD' etc, but most of the these cameras can be manually adjusted away from default settings, so, IMHO, it's a moot point, and is pointless to really mention, learn how to use your camera ;)
You're not demanding, you just know what you want :)
yyrkoon - Wednesday, September 27, 2006 - link
Forget what all the nay sayers are saying guys, write you articles. I've been interrested in the Sony A100 for several months now, since the preview on dpreview.com. I also think you're right concerning the *mass* of information that dpreview gives off for thier camera reviews, most of it is un nessisary for all but the professionals, most of us just want to know things like, how many FPS does the camera achieve, how does it handle low light situations, how clean are the photos, etc.Carry on :)
silver - Wednesday, September 27, 2006 - link
Another good point. AT has always been about presenting good, practical information on the products that we use and in this context has always done a great job.The A100 certainly has my intrest as well but do note that most pro's do not need bells and whistles in their equipment. In fact most don't even want them available as it adds to both cost and complexity with almost no practical return in value.
Lord Midas - Wednesday, September 27, 2006 - link
Very good article Wesley. Thanks.Still a lot of this is still baffling at the moment but that should change when I get my Canon Rebel XTi 400D for Christmas.
What I would like to see in the reviews would also include the quality of the bundled lens (the Canon comes with the 18-55mm lens). As well as with a quality lens.
Will you also include reviews of lens:
For example you do the "Mid Range GPU Roundup - Summer 2006"
So you could do this with Normal, telephoto, etc lens.
So instead of reviewing one lens you can do a group test.
And I also think that a few standard photos for all the reviews would be good (indoor, outdoor, macro, etc) and a few random ones the the reviewer would think we would like.
Keep up the good work. Thanks.
mesonw - Tuesday, September 26, 2006 - link
Just wanted to add my 2p-worth. I feel I fit fairly well into the target audience you're aiming at. I'm very lacking when it comes to the technical details of cameras, digital or otherwise, yet I have a great desire to take good and interesting pictures.It's good for people to offer tips and ideas for your upcoming articles, but I don't see the point of the very knowledgeable and camera-savvy crowd out there making harsh criticisms simply because you're targetting people with less knowledge than them. Like they say, there are other sites to get in-depth information if they want it, so why berate AT for catering for others?
I for one look forward to your articles on the subject, because I know they will be well written, provide useful information and insights, and very likely make me a better amateur photographer.
Good work AT.