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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silver - Tuesday, September 26, 2006 - link
No Adaptall for digital cameras ?tsapiano - Wednesday, September 27, 2006 - link
Well, most DSLRs use the same lens mount as their film-based predecessors so you can use things like Adaptall on the new cameras as well if you really want. The problem with that is that this technique was pretty much abandoned a while ago, so to do this you'd be stuck using old aftermarket lenses. While it was relatively easy to make a universally adaptable lens when everyone was using simple mechanical couplings - the electronic communication used in modern lenses has made that much more complicated. As such, most modern aftermarket lenses are now generally built and sold specifically for the mount you are using.With that said, there are simple adapters that you can buy to mount Nikon, Leica, Contax, Olympus OM and Pentax lenses on Canon EF bodies. As the Canon mount has a smaller register (ie the mount is closer to the film plane) and wider opening than all of those mounts, it makes it possible to fit an adapter in there. The catch-22, however, is that these are very simple adapters and don't do much other than mechanically attach the lens to the camera - you loose aides like autofocus, aperture must be set on the lens (ie A or M exposure modes only), you're forced to revert to stop down metering, etc. As such, while this may be useful to use a special purpose lens or two it's not really what you want to do for your everyday photography ;)
Resh - Tuesday, September 26, 2006 - link
Nope.Wesley Fink - Monday, September 25, 2006 - link
No, Canon lenses fit Canon only, and same with Nikon. Each brand will only fit their own lenses and independent lenses made for that clens mount. Samsung licensed their lenses from Pentax and they will fit Samsung and Pentax. Sony bought Minolta so Sony and Minolta lenses both fit.nigham - Monday, September 25, 2006 - link
I'm really happy that AT is getting to digital SLR camera reviews. This article was slightly disappointing. As has been pointed out, anyone who doesn't know his or her f-stops and shutter speeds should certainly not be spending money on a Digital SLR just yet. My experience with my prosumer Canon S2IS says that it takes a while to _really_ appreciate these settings and they're not simply learned theoretically. And I don't particularly care for history, but maybe thats just me.That said, it's OK since I've only seen one real good DSLR introduction for beginners (http://www.firingsquad.com/hardware/panasonic_lumi...">here), and what matters most are the reviews, which I'm hoping will measure up to the usual AT standard. Here's what I'd like:
- Feature description and (in prose) comparisons to comparable and current cameras. What's really improved, and what's just marketing? etc.
- How good the documentation is. This is something woefully ignored by many camera review sites.
- Reference testing with a high-quality lens; since I would expect to be buying lenses eventually if I get a DSLR
- A section (maybe short) evaluating the quality of the in-kit lenses
- Battery tests (these are important! unlike that startup times in which case I totally agree with you). Also options for backup batteries (how expensive, availability)
- A (necessarily subjective) description of the "feel" of the camera output in various real-world scenarios like landscape, low-light, fast-motion etc.
- A human-readable description of how easy/difficult the UI is. I do not want a list of menu options five levels deep and 20 EVF screenshots, I need you to take a call and let me know what the bottom line is. How hard is it to change the basic stuff (F-stop, ISO, WB?); are there any customizations available; are there any quirks like controls that inadvertently get messed around with; does it have a on-screen histogram?
- How good the AUTO mode is, and when it fails. Personally, I believe that the primary job of a photographer is to see the photo and compose it. I'd like to know when I can afford to go auto and spend more time composing my shot, and when I can't do that.
- A set of sample photos in real-world situations
I think it would be nice to remember that even for hard-core computer enthusiasts, photography remains an art and is not easily described; and is nearly impossible to describe with numbers alone.
Lastly, I'd really appreciate an article on RAW workflow - if possible one that includes a discussion of the ways Linux handles DSLRs. That is something that changes quite a bit for users transitioning to DLSRs.
Resh - Monday, September 25, 2006 - link
Sorry, just can't agree with that. How can the inter-related tasks of exposure, choosing focus point, and depth of field be separated from composition?
mostlyprudent - Monday, September 25, 2006 - link
One thing I forgot in my earlier post (and forgive me if it has already been mentioned), I would like to see more on lenses. I think AT should test both the Kit lense and a high quality reference lense. I wouldlike to know both how good the camera can be with a great lense and how good of a value the kit lense offers.Thanks.
Resh - Monday, September 25, 2006 - link
I thought it was a good primer for beginners and was full of useful history, but couldn't shake the feeling that AT was trying to crowd into an already crowded room.While I fully agree with those who have pointed-out that a diversity of reviews is a good thing, I think that diversity already exists with sites like Steve's Digicams, DPReview, etc. In addition to those we have more art, in-the-field sites like Luminous Landscape that focus on how a product performs in the field.
Some have argued that AT should do reviews to the level of detail/bench-marking that is employed for motherboard and video cards. Here, I have a harder time as I don't see an SLR body as being comparable to those components.
AT reviews those parts in the context of choosing one to fit into a larger computer system. Alternatively, an entire system (e.g., Alienware) is tested against a home-built system with similar specs or at similar cost. This model, however, doesn't appear relevant to the SLR market as one cannot individually buy the processor, sensor, body, etc. that is the best and construct their own camera. Rather, a first time buyer chooses an entry point into a given manufacturer's "system" based on the body's attributes; lens cost, availability, and quality; and available accessories. For someone upgrading their SLR, the choices are even less driven the details that AT would likely be assessing. Rather, they'd be considering the costs of switching systems (e.g., from Canon to Nikon), or simply considering the value of upgrading to the latest and greatest, a question that existing sites can answer just fine.
All that to say that there are areas where current sites fail and where AT's expertise might be better leveraged. The main example, for me, is in the area of displays and printers. With regard to the former, quality CRTs are gone and LCDs present a purchaser with huge variability in cost, performance, and quality. AT could look at the display market from the photographer's point of view (appropriate brightness coupled with stable contrast, wide-colour gamut, ease of calibration, wide viewing angles, etc). This could be supplemented with discussion of colour calibration products. Similarly for printers, there is little to be found on-line that offers critical comparison of competing printers on different papers. Both of these areas would fit well within AT's current review framework.
Lastly, AT, while not a software site, could elevate the standards of software reviews by taking a hard look at the effects of different RAW converters, enlargement software, sharpening tools, and noise reduction software. I have not seen anyone do this in an objective, scientific manner.
AT is a fantastic site and while I applaud your willingness to branch-out, I am cautious about your getting too far from your core audience and your core strengths.
N
s12033722 - Monday, September 25, 2006 - link
It would be good to delve into the nature of how image sensors work and the differences between types of sensors. I think Anandtech would be an excellent place to discuss these aspects of the cameras.Image sensors basically work by photons interacting with light-sensitive portions of the sensor to create electrical charge. The efficiency of the sensor at converting photons into electrons is reffered to as quantum efficiency, and has a serious impact on how well a camera will perform under different imaging conditions. After the charge is collected, in the case of a CCD sensor, the charge is read out of the sensor, passed through a processing chain, and then digitized. It is important to note that this is an ANALOG process until the point of digitization. In the case of a CMOS sensor, the digitization may occur at each pixel on the sensor, at the end of each row or column of pixels on the sensor, or off sensor like the CCD. Each approach has advantages and disadvantages, generally trading off noise performance for pixel size.
Image sensors are characterized by a number of factors. Noise, dynamic range, pixel size, and so forth tend to be interrelated. The comment in the article about dynamic range was somewhat simplistic. Dynamic range is primarily governed by the charge capacity of the pixel. A sensor will be characterized by a quantum efficiency as noted above, which means that as more photons strike the sensor, a greater charge will be built up. If a very bright spot exists on the image, that spot will usually fully charge the pixels under that spot, limiting the output at that level. For instance, let's say a pixel has a full-well charge capacity of 30,000 electrons, and that there is no noise. The dimmest pixel possible on the image would be 1 electron (well, 0, but let's say 1) and the brightest would be 30,000, for a dynamic range of 30,000 to 1. Now, in reality there are noise sources in a sensor. Many of them. That will typically mean that the dimmest pixel will have a charge on it, which reduces the dynamic range. Perhaps there are 500 electrons of noise. Now the sensor has a dynamic range of 30,000 to 500 or 60 to 1. Far less. The ways to increase dynamic range are to decrease noise or to increase charge capacity. Unfortunately, charge capacity is directly tied to the physical size of the pixel, so as resolutions get higher, pixel size gets smaller, and dynamic range suffers. It is entirely possible to build sensors with dynamic ranges that meet or exceed those of film, but generally not within the size constraints imposed by sensor size and the perception of resolution as king by most consumers. When was the last time you saw the dynamic range or noise performance advertised on a camera? Even though these are arguably far more important than resolution to most SLR purchasers, these details are glossed over.
I would like to see a basic overview of the guts of a digital camera given. Sensors, data conversion, data processing, autofocus mechanisms, etc. Anandtech seems like a good site to do it. Contact me if you need help or technical details.
Curt - Monday, September 25, 2006 - link
Could you include in your reviews astronomy photos? As an amateur astronomer, I'd be interested in comparing the very low light sensitivy and contrast ratios of the CCD's.Thanks in advance