Digital Photography from 20,000 Feet
by Wesley Fink on September 25, 2006 12:05 AM EST- Posted in
- Digital Camera
Photo Basics: Painting with Light
It is very important to understand that whether using digital still photography, digital movies, film stills, or film movies the principals of capturing images is the same. In every case you are capturing images of light on some photosensitive medium. While many people want nothing more than the automatic point-and-shoot available on every digital camera these days, understanding what is happening behind the scenes can help you in selecting the right tools for what you want to do - even if you never plan to use those features.
ISO Speed: The Sensitivity of the Digital Sensor
With 35mm film cameras, an important decision before shooting any photos was what film to buy. Films varied not just in types (slide and print) but most importantly in speed - the ability of the film to respond to light. Film varied from some super-fine-grained ASA 25 to some faster, but grainer, ASA400. Late in film development the most commonly used films were ASA50 to 100 for quality shots when you had plenty of light, and ASA400 to 800 where light was low and you could live with the increased "graininess" of the images.
Several competing film speed systems existed - the US ASA, European DIN, and the Soviet GOST to name a few. All of these systems for measuring film speed were eventually replaced by the ISO system, which basically combined the ASA and DIN systems.
Digital photography has completely changed our ideas of film speed, since the sensor is built into the camera. We no longer have to worry about film speeds or changing film, but digital sensors still use ISO speed to measure their sensitivity. The great thing about digital sensors compared to film, though, is that digital sensors in SLR cameras have a wide range of sensitivity speeds, and you can just choose how sensitive you want the sensor to be. It helps in choosing ISO if you understand what it means.
ISO, or the International Organization for Standardization, eventually developed a standard which combined both the ASA (linear) and DIN (logarithmic) scales into one ISO standard, officially ASO5800:1987. The most common ISO film speed ratings are:
25/15°, 50/18°, 100/21°, 200/24°, 400/27°, 800/30°, 1600/33°, and 3200/36°
The important point to understanding ISO is that a doubling of film speed means the film (or sensor) is twice as sensitive to light. On the logarithmic scale a change of 3° is a doubling of sensitivity. So each number above represents twice the sensitivity of the previous number.
What this means is that at the same shutter speed and aperture (lens setting) you can take pictures in 1/8 the light by using ISO 800 instead of ISO 100. Early digital cameras and digital point-and-shoots often only support a few ISO sensitivities (50, 100, 200) and they rarely support sensitivities above ISO 400. The Digital SLR, on the other hand, normally supports ISO speeds to 1600 or even 3200 on some cameras. This gives the user great flexibility in low light.
There is a trade off, however. As speed increases some digital SLRs do a much poorer job of resolving details in the picture. All Digital SLR cameras seem to do fine from 100 to 400, most go to ISO 800 easily, and some do to ISO 1600 with minimal loss of image detail. In reviewing a camera look at the effects of ISO speed on image quality.
Every digital SLR allows the user to adjust ISO speed, but some make it easier than others. The new Sony A100, for example, has an "Auto" ISO setting that automatically adjusts ISO between 100 and 800 depending on the light in the scene. The new Nikon D80 allows the user to customize the Auto ISO range depending on what they are comfortable with.
In the end, you can adjust ISO, the lens aperture (f-stop), or shutter speed to control the amount of light that strikes the sensor. Any of the three can control the light, and they all have different effects and different limitations. The Auto programs in all digital SLR cameras make these decisions for you, but it is good to know what they are doing in the background, or how to manually make these decisions yourself. One of the great advantages for digital users is that the sensor can operate at many speeds, not just one, and the rest of the "film" is a flash memory that you can reuse over and over. Nothing is consumed in the digital photo process until you want hard images (prints).
It is very important to understand that whether using digital still photography, digital movies, film stills, or film movies the principals of capturing images is the same. In every case you are capturing images of light on some photosensitive medium. While many people want nothing more than the automatic point-and-shoot available on every digital camera these days, understanding what is happening behind the scenes can help you in selecting the right tools for what you want to do - even if you never plan to use those features.
ISO Speed: The Sensitivity of the Digital Sensor
With 35mm film cameras, an important decision before shooting any photos was what film to buy. Films varied not just in types (slide and print) but most importantly in speed - the ability of the film to respond to light. Film varied from some super-fine-grained ASA 25 to some faster, but grainer, ASA400. Late in film development the most commonly used films were ASA50 to 100 for quality shots when you had plenty of light, and ASA400 to 800 where light was low and you could live with the increased "graininess" of the images.
Several competing film speed systems existed - the US ASA, European DIN, and the Soviet GOST to name a few. All of these systems for measuring film speed were eventually replaced by the ISO system, which basically combined the ASA and DIN systems.
Digital photography has completely changed our ideas of film speed, since the sensor is built into the camera. We no longer have to worry about film speeds or changing film, but digital sensors still use ISO speed to measure their sensitivity. The great thing about digital sensors compared to film, though, is that digital sensors in SLR cameras have a wide range of sensitivity speeds, and you can just choose how sensitive you want the sensor to be. It helps in choosing ISO if you understand what it means.
ISO, or the International Organization for Standardization, eventually developed a standard which combined both the ASA (linear) and DIN (logarithmic) scales into one ISO standard, officially ASO5800:1987. The most common ISO film speed ratings are:
25/15°, 50/18°, 100/21°, 200/24°, 400/27°, 800/30°, 1600/33°, and 3200/36°
The important point to understanding ISO is that a doubling of film speed means the film (or sensor) is twice as sensitive to light. On the logarithmic scale a change of 3° is a doubling of sensitivity. So each number above represents twice the sensitivity of the previous number.
What this means is that at the same shutter speed and aperture (lens setting) you can take pictures in 1/8 the light by using ISO 800 instead of ISO 100. Early digital cameras and digital point-and-shoots often only support a few ISO sensitivities (50, 100, 200) and they rarely support sensitivities above ISO 400. The Digital SLR, on the other hand, normally supports ISO speeds to 1600 or even 3200 on some cameras. This gives the user great flexibility in low light.
There is a trade off, however. As speed increases some digital SLRs do a much poorer job of resolving details in the picture. All Digital SLR cameras seem to do fine from 100 to 400, most go to ISO 800 easily, and some do to ISO 1600 with minimal loss of image detail. In reviewing a camera look at the effects of ISO speed on image quality.
Every digital SLR allows the user to adjust ISO speed, but some make it easier than others. The new Sony A100, for example, has an "Auto" ISO setting that automatically adjusts ISO between 100 and 800 depending on the light in the scene. The new Nikon D80 allows the user to customize the Auto ISO range depending on what they are comfortable with.
In the end, you can adjust ISO, the lens aperture (f-stop), or shutter speed to control the amount of light that strikes the sensor. Any of the three can control the light, and they all have different effects and different limitations. The Auto programs in all digital SLR cameras make these decisions for you, but it is good to know what they are doing in the background, or how to manually make these decisions yourself. One of the great advantages for digital users is that the sensor can operate at many speeds, not just one, and the rest of the "film" is a flash memory that you can reuse over and over. Nothing is consumed in the digital photo process until you want hard images (prints).
Facebook
Twitter
RSS
81 Comments
View All Comments
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.