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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feraltoad - Monday, September 25, 2006 - link
Is providing a single sentence regarding start-up time dwelling? I don't think any camera review is complete without listing startup times and listing shot to shot time. I think it's a bit hypocritical to focus on core architecture, timings and such and then say a length of time I can actually perceive is not relevant. Especially, when you go and provide such a good article. I think you are just trying to make the other review sites seem stodgy and backward or just wrongheaded, and show that AT is "with it". Moreover, you say they speak gibberish like they are jargon slinging photo elitist snobs. Then you provide,IMO, a pretty techical primer, when they probably have some material for novices too. I know you were just saying "We're Cool, We Rule!", but I don't think when ur AT you have to do that. AT is already in my RSS reader because it does quality reviews. I just skimmed the article, and I can't wait to go back and read it in depth. I'me really excited about AT doing photo stuff too. I agree with the above poster that finding some standard meaningful benchmarks with good subjective commentary will have AT ruling the roost in camera reviews. Not to plug another site, but I think Steve's Digicams provides excellent reviews, actually his site is about the only site I really find useful for cameras. I'm glad I will soon have two sites that provide good information. YAY AT!soydios - Monday, September 25, 2006 - link
How does AnandTech review and compare its computer components? With standardized benchmarks and editorial commentary. Compare all the cameras with a good, strong set of standardized tests across the board, and also add a dose of the editorial commentary.In particular, for the sub-$1000 market, I would suggest evaluating the kit as a whole (image quality with kit lens). Personally, I will be picking up a Nikon D50 with the 18-55mm and 55-200mm lenses, and I have researched the heck out of that package, trying to find an AnandTech-esque review.
Venturing above the sub-$1000 (although I would be very intrigued by some reviews of the professional-level equipment) would get very expensive very fast. Perhaps start small, then venture into the almost-pro market (Nikon D200 and Canon EOS 30D, and some of the $500-$1000 lenses), then maybe dip a toe into the professional level, just to let us all see what the real fancy stuff is like (since very few of us will be buying a D2Xs or EOS-1D MkII-N).
Time permitting, I would put out some quick looks at the Nikon D50 and the Canon EOS 350D, with some comparison between the two. A review/comparison of both the Nikon D80 (in the works, good!) and the Canon EOS 400D would be an interesting read.
Again, review the D-SLR market the same way you guys do computer hardware. Avoid the slugfest low-range and the stratospherically-priced high range. Focus on the high-midrange market (the sub-$1000 D-SLR's to start, move up to the $1k-2k market once you gain some feel for differences between cameras). Do across-the-board standardized benchmarks, with some synthetic but more real-world results.
mostlyprudent - Monday, September 25, 2006 - link
Exactly my thoughts. I have spent some time at a number of camera review sites and am always left wondering "Is the Nikon D80 good enough to justify the price difference over the D50?". "What about the Canon EOS 30D? How much better is it then the Nikon D80 or the Rebel XT/XTi?"Maybe these cannot be answered in the same way as CPU and GPU articles, but standardized tests and comparisons would be nice.
Give me some numbers! I don't want to hear "shot-to-shot performance was sluggish compared to higher end cameras"...unless you can quantify that for me.
Lighting is such an improtant part of photography. Standardized indoor lighting under a couple different kinds of lighting situation (i.e. low, bright, fluorescent, etc.). I don't know how to standardize outdoor shots, but it sure would be nice.
bigpow - Monday, September 25, 2006 - link
I'm gonna stick with www.dpreview.com for now if I want to get my digital photography news/articles.AT, stick with PCs, will you?
silver - Monday, September 25, 2006 - link
I don't understand as I usually read more than one site on one subject. For instance I've been reading Tomshardware since it was sysdoc.pair.com and both Anandtech and Extremetech nearly as long.jnmunsey - Monday, September 25, 2006 - link
Geez, you'd think a site like Anandtech would find someone who knows what he's talking about to write this article...soydios - Monday, September 25, 2006 - link
I'm just a photography hobbyist, but I thought that the article covered all the important basics of full-manual general photography and digital photography.I would touch on filters, though. Those can come in handy. Particular onces to focus on: UV ("does it actually do anything, or is it just a lens protector?" debate), Polarizing, and the primary colors (blue, yellow, and red).
soydios - Monday, September 25, 2006 - link
Concerning polarizing filters (I really wish there was an edit functionality for comments): circular polarizing works with autofocus and digital cameras, linear does not.I know AnandTech isn't much of a software website, but a short article on editing software (Adobe Photoshop, beta of Adobe Lightroom, Apple Aperture) would complete the picture. No need to focus on the software or printing, but a photography software article written in the same manner as this one is something that would help me a lot! (I have almost no experience with editing software).
Wesley Fink - Monday, September 25, 2006 - link
We all want to improve, so please provide specifics so we can address them. It would also be helpful if you would provide your photography credentials, so we can know the level of expertise to attach to your comments.kilkennycat - Monday, September 25, 2006 - link
... a first-class and technically-meaty summary of the current status of digital camera technology. Well up to the usual Anadtech standards. Congratulations, Wes. The addition of a Digital Camera section is a superb idea. By all means, use reference charts, lighting and scenes for resolution, optical-distortion, shading and color-fidelity comparison of both lenses and sensors. Just as you have with video cards and CPUs, come up with your own benchmarks if necessary.