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).
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silver - Monday, September 25, 2006 - link
I think this is one tidbit that you might write on when you're realy bored. My images are backed up using Verbatim UltraLife Gold DVD-R media. You also need to make sure that they stay cool and dry much as you do with film. They're not as sensitive to humidity but as certainly far more sensitive to heat.Googer - Monday, September 25, 2006 - link
Panasonic is makeing and selling cameras based on good old Leca Lens. If you have a leica lens from any point in the last 55+ years, it will be compatable with a Panasonic/Leica Camera.
Wesley Fink - Monday, September 25, 2006 - link
The Pansonic Lumix DMC-L1 digital SLR uses a Leica lens built with a four thirds mount. This is the new digital only mount pioneered by Olympus. The LMC-L1 is mentioned in the guide.silver - Monday, September 25, 2006 - link
One of my friends has one of these and the images are simply incredible. He states that the Opticla Image Stabilization is simply the best he could find.wilburpan - Monday, September 25, 2006 - link
As someone used to shooting with film cameras, I can say that I still notice some shutter lag when using digital SLRs, even with current models. To write this off as "Virtually none of the lags of early digital cameras remain" is to ignore a real factor when it comes to the use of any camera.To put this another way, if a digital camera website stated that the choice of CPUs was unimportant in buying a computer because all modern day CPUs were fast and powerful enough, the readers of this site probably would bust a gut.
There are also speed issues involved with other uses of a digital camera that need to be addressed. The Nikon D80 takes about 1.4 seconds to store and then display an image after the shutter has been pressed. The speed of this process varies widely from camera to camera. Similar variances in speed and performance come into play when performing tasks such as playback of pictures taken, the time that it takes to process bursts of photos when shooting in continuous mode, etc.
silver - Wednesday, September 27, 2006 - link
Regarding shutter lag, digital cameras will always be slower than film. There's no way around that. My FM2n's have near instantaneous shutter release and are quite the opposite of my admittedly dated Fuji S602. What manufacturers need to do is to have separate power sources (batteries) for lens focusing and camera functions other than CCD/CMOS/memory charging. Obviously this would complicate the camera so they probably aren't considering this option.Wesley Fink - Monday, September 25, 2006 - link
This is where we start to get into questions about what test is real. The file flush time on a Nikon D80 is 2.0 seconds for a fine jpeg and a little less than 3s for a RAW+jpeg. However, you never encounter this becuase of the memory buffering built into the Nikon D80 and every other digital SLR camera. The D80 can do 3 fps for a little over 30 seconds shooting raw+jpeg, and with fine jpeg it can shoot 3fpm until you run out of flash card room or battery.I consider the D80 time of 160ms viewfinder blackout (0.16s), and a less than 0.1s from off to shot negligible for almost any users. Even the Sony, which has a 1 second start-up, is using almost all that time to clean the sensor before shooting, while shot-to-shot is very competitive with the best SLRs around. Some users might be happier if you could turn off the cleaning on start. While this may be very important for some users, it is doubtful that the small differences in recent digital SLR cameras will really be noticable or matter to most users.
dpreview is an excellent and respected digital review site, and I have sent many readers there with their questions. They often come back with more questions than answers, which usually means they found the technical level too far above their skills and needs. We can't be all things in Digital Camera reviews so we will likely err toward the more basic side.
We'll consider your suggestion about start-up times, but I'm not convinced yet.
yacoub - Monday, September 25, 2006 - link
I appreciate your article but I don't know: I think that folks into digital photography, no matter what other hobbies they have, including computer hardware or gaming, are knowledgable enough (or are competent enough to gain the knowledge needed) to make good use of a site like DPReview, which offers about all the info most need to make an intelligent purchase of a digital camera. Plus that being their primary focus (and has been for years), they automatically get much more credibility than a computer hardware site can hope to achieve by writing content basically saying "look we can do this too!" and writing what most good highschool photography classes are teaching today anyway.I guess my question is, why not stay focused on computer component hardware? All branching out does is reduce the chance of the main hardware getting the attention it needs. There are umpteen motherboard, videocard, and RAM reviews and guides yet to be completed or even begun, yet you're going off into digital photography land? That's kind of disappointing. For that hobby there are already many strong resources for folks who are into that, and many more for folks who want a simple pocket-sized point-n-shoot (which is the majority of folks). Why not focus on being the strong resource in computer hardware that folks in this hobby need?
fanbanlo - Monday, September 25, 2006 - link
Maybe AnandTech can explain to use what are the new technology built into the sensor rather than meaningless marketing terms givin to them.Different algorithm used? what's their computational power?
Why shoot RAW? RAW-enabled software review!?
Thx
Heidfirst - Monday, September 25, 2006 - link
For the lower end DSLRs (D50,350D,K100D etc.) I think that you should also review the standard kit lens as the majority of buyers will probably be buying it with the body as a package.By the time that you start hitting EOS30D type level imo most people will probably have lenses already or be buying a better lens than the entry level kit lens. Also if they are paying that for a body they quite probably are reasonably knowledgeable photo enthusiasts & maybe Anandtech isn't going to be the first place that they look for reviews so sticking to the lower end at least initially sounds reasonable to me.
The idea of a standard test scene is interesting but it would have to be reproducible which means in the studio & that means that it's less representative of the conditions in which most people will use them (I imagine that the % of even current DSLR users who shoot in the studio is in single figures & probably low single figures at that).