Digital Photography from 20,000 Feet
by Wesley Fink on September 25, 2006 12:05 AM EST- Posted in
- Digital Camera
Understanding 35mm and Digital Lenses
If you have no interest in understanding what different lenses do and when to use them, then don't buy a Digital SLR. The main reason SLR exists is to offer a flexible platform for using a wide range of lenses. You could justify the quality aspect and through the lens viewing, but you can find those features on fixed lens cameras. People who buy a digital SLR with one lens they never change and never intend to change are basically wasting their money - they should buy a quality point-and-shoot or fixed lens SLR.
Image Size
To understand how different lenses behave and which lens to use in digital photography we need to go back to 35mm basics. Early 35mm cameras generally shipped with a single focal length "normal" lens. "Normal" is defined as the approximate point of view of your single eye when looking at a scene. That is, if you keep both eyes open when looking through a viewfinder, a camera with a normal lens will look about the same as what the other eye not looking through the lens sees. It is easy to determine the "normal" lens focal length for any image size - it is approximately equal to the diagonal of the image size, which is obviously about the same as the field of view if you consider that as a circle.
This means a normal lens for 35mm would be about 45mm. For those who enjoy history you might be interested to know that the 35mm normal lens got defined as 50mm by Oskar Barnack, the creator of the Leica camera. At the time lens technology could produce sharper lenses if they were slightly longer than normal, so Barnack defined normal as 50mm on the early Leicas. The definition stuck, but most would agree normal on 35mm is anywhere between 40 and 58mm. Lenses with shorter focal lengths than normal are called wide angle, because they see more than the normal lens, and longer focal lengths are called telephoto.
You can see from the chart above that "normal" for APS C size, used in most digital SLRs, is about 28mm - and not the 45mm to 50mm typical of 35mm. The digital normal is a little more complicated than the simple math of film normal, because it got defined in the 1950s by TV tube size (normal is about 2/3 TV tube size). However, the real image size for APS C in digital ranges from about 22.7mm x 15.1mm to 23.7 x 15.8mm (sometimes called DX). This means that 28mm is close enough for this discussion.
For those of you who have looked at Digital Camera specs and wonder what a 1/1.8" sensor means in point-and-shoot digital specifications, it means an image size of 7.18mm x 5.32mm - MUCH smaller than the 22.7mm x 15.1mm of APS C. You can see the translations in the chart below of digital.
Since the imaging companies are convinced that consumers understand 35mm lens ranges you will find most point-and-shoot cameras define their zoom or fixed lenses as equivalent 35mm specifications. When you see a Kodak P880, for example, defined as a 24-140mm zoom lens you might also notice it uses a 1/1.8" sensor. Since that sensor is about 9mm at normal, the true focal length of the lens is somewhere around 4-28mm. By calling it 24-140mm the manufacturer hopes the potential buyer understands the zoom range in common terms.
If you have no interest in understanding what different lenses do and when to use them, then don't buy a Digital SLR. The main reason SLR exists is to offer a flexible platform for using a wide range of lenses. You could justify the quality aspect and through the lens viewing, but you can find those features on fixed lens cameras. People who buy a digital SLR with one lens they never change and never intend to change are basically wasting their money - they should buy a quality point-and-shoot or fixed lens SLR.
Image Size
To understand how different lenses behave and which lens to use in digital photography we need to go back to 35mm basics. Early 35mm cameras generally shipped with a single focal length "normal" lens. "Normal" is defined as the approximate point of view of your single eye when looking at a scene. That is, if you keep both eyes open when looking through a viewfinder, a camera with a normal lens will look about the same as what the other eye not looking through the lens sees. It is easy to determine the "normal" lens focal length for any image size - it is approximately equal to the diagonal of the image size, which is obviously about the same as the field of view if you consider that as a circle.
| Traditional Film Image and Lens Characteristics | |||
| Film format | Image dimensions | Image diagonal | Normal lens focal length |
| APS C | 1.67 cm x 2.51 cm | 30.15 mm | 28 mm, 35 mm |
| 135 | 2.4 cm x 3.6 cm | 43.27 mm | 50 mm, 45 mm |
| 120/220, 6 x 4.5 (645) | 5.6 cm x 4.2 cm | 70.00 mm | 75 mm |
| 120/220, 6 x 6 | 5.6 cm x 5.6 cm | 79.20 mm | 80 mm |
| 120/220, 6 x 7 | 5.6 cm x 6.8 cm | 88.09 mm | 90 mm |
| 120/220, 6 x 9 | 5.6 cm x 8.2 cm | 99.30 mm | 105 mm |
| large format 4 x 5 sheet film | 10.16 cm x 12.7 cm (4" x 5") | 162.64 mm | 150 mm |
| large format 8 x 10 sheet film | 20.32 cm x 25.4 cm (8" x 10") | 325.27 mm | 355 mm (14") |
This means a normal lens for 35mm would be about 45mm. For those who enjoy history you might be interested to know that the 35mm normal lens got defined as 50mm by Oskar Barnack, the creator of the Leica camera. At the time lens technology could produce sharper lenses if they were slightly longer than normal, so Barnack defined normal as 50mm on the early Leicas. The definition stuck, but most would agree normal on 35mm is anywhere between 40 and 58mm. Lenses with shorter focal lengths than normal are called wide angle, because they see more than the normal lens, and longer focal lengths are called telephoto.
You can see from the chart above that "normal" for APS C size, used in most digital SLRs, is about 28mm - and not the 45mm to 50mm typical of 35mm. The digital normal is a little more complicated than the simple math of film normal, because it got defined in the 1950s by TV tube size (normal is about 2/3 TV tube size). However, the real image size for APS C in digital ranges from about 22.7mm x 15.1mm to 23.7 x 15.8mm (sometimes called DX). This means that 28mm is close enough for this discussion.
For those of you who have looked at Digital Camera specs and wonder what a 1/1.8" sensor means in point-and-shoot digital specifications, it means an image size of 7.18mm x 5.32mm - MUCH smaller than the 22.7mm x 15.1mm of APS C. You can see the translations in the chart below of digital.
| Digital Image and Lens Characteristics | ||||
| Sensor type | TV-tube diameter | Image dimensions | Image diagonal | Normal lens focal length |
| 1/3.6" | 7.1 mm | 4.00 x 3.00 mm | 5.00 mm | 5 mm |
| 1/3.2" | 7.9 mm | 4.54 x 3.42 mm | 5.68 mm | 5.7 mm |
| 1/3" | 8.5 mm | 4.80 x 3.60 mm | 6.00 mm | 6 mm |
| 1/2.7" | 9.4 mm | 5.37 x 4.04 mm | 6.72 mm | 6.7 mm |
| 1/2.5" | 10.2 mm | 5.76 x 4.29 mm | 7.2 mm | 7 mm |
| 1/2" | 12.7 mm | 6.40 x 4.80 mm | 8.00 mm | 8 mm |
| 1/1.8" | 14.1 mm | 7.18 x 5.32 mm | 8.93 mm | 9 mm |
| 1/1.7" | 14.9 mm | 7.60 x 5.70 mm | 9.50 mm | 9.5 mm |
| 1/1.6" | 15.9 mm | 10.5 mm | ||
| 2/3" | 16.9 mm | 8.80 x 6.60 mm | 11.00 mm | 11 mm |
| 1" | 25.4 mm | 12.80 x 9.60 mm | 16.00 mm | 16 mm |
| 4/3" | 33.9 mm | 18.00 x 13.50 mm | 22.50 mm | 23 mm |
| (APS-C) 1/8" | 45.7 mm | 22.70 x 15.10 mm | 27.3 mm | 27 mm |
| DX | n/a | 23.7 x 15.8 | 28.40 mm | 28 mm |
| FF (35 mm film) | n/a | 36 x 24 mm | 43.30 mm | 50 mm |
Since the imaging companies are convinced that consumers understand 35mm lens ranges you will find most point-and-shoot cameras define their zoom or fixed lenses as equivalent 35mm specifications. When you see a Kodak P880, for example, defined as a 24-140mm zoom lens you might also notice it uses a 1/1.8" sensor. Since that sensor is about 9mm at normal, the true focal length of the lens is somewhere around 4-28mm. By calling it 24-140mm the manufacturer hopes the potential buyer understands the zoom range in common terms.
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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.