I would like to repeat that this tutorial is directed at woodworkers, not photographers. What I will cover relates to how a woodworker can use photography to enhance his/her woodworking. Generally this means photographing stills for a portfolio, website, blog, or even capturing wood grain to use for texturing a SketchUp model. What we will not discuss, and what is not implied in anything I cover, is nature photography, portraiture, sports photography, macro photography etc. The camera, lenses, other accessories, techniques, software et al are often different between photographic styles. Today we are going to focus on the camera, or more specifically the camera body; its features and specifications that make it more suitable for woodworking photography.
Digital Single Lens Reflex – DSLR
The preferred camera, and the only one we will discuss here, is the Digital Single Lens Reflex or DSLR camera. These cameras are very similar to their 35mm cousins, although both SLR and DSLR have replaced largely mechanical innards with almost entirely electronic innards these days. What is important about an SLR is that you see in the viewfinder exactly what the lens sees. In fact, the viewfinder is getting its image by redirecting a portion of the light that passes through the lens to the viewfinder with the aid of a mirror.
Not only does the viewfinder see what the lens sees but it can also see the depth-of-field (DOF) produced by the lens and its f/stop setting. This is accomplished by depressing a DOF preview button, available on most DSLR cameras. This button stops down the aperture diaphragm which allows you choose an f/stop that will produce the desired DOF which can be evaluated in the viewfinder.
Many DSLR cameras have an exposure mode selection that is essentially a DOF priority mode, much like aperture priority or shutter priority. On my Canon cameras it is called A-DEP for automatic depth-of-field. What A-DEP does is automatically choose an f/stop that will maximize the DOF for most of what is in the scene. It then chooses an ISO and shutter speed that will give correct exposure.
In both of these cases, either manual setting of f/stop or A-DEP, you are likely to end up with a small aperture and long shutter speed, because you will want the maximum DOF to ensure your woodworking piece is in total focus. Long shutter speed means camera blur unless a tripod is used, and that is why a tripod was listed as necessary equipment in Part 1. Almost all the photographing we will do as a “woodworker photographer” will be with a tripod.
While we are still on SLR features, many of the new DSLRs have a feature that allows you to see the image on the LCD instead of the viewfinder. On the Canon this is called Live View. Normally, when shooting hand held, I would never use this feature. But it does come in handy when the camera is mounted on a tripod, especially when the height of the viewfinder ends up higher or lower than eye level. It also allows both manual and auto focus. In addition, for manual focus, you can zoom the LCD 5X or 10X for easier and more accurate focusing. This is a really nice feature when shooting on a tripod.
ISO – As In Film Speed
ISO is an acronym for International Standards Organization (more precisely International Organization of Standards). In photography it refers to the standards adhered to by film manufacturers or digital camera manufacturers. Remember when you went to the drug store and bought ASA 100 film for outdoor shooting, or ASA 400 for indoor shooting? Well, ASA and ISO are equivalent arithmetic scales that define the amount of light a film required for correct exposure. ASA or ISO 100 film required twice as much light for correct exposure as did ASA or ISO 200, and four times as much as ASA or ISO 400. When digital cameras came along the manufacturers adhered to the same ISO standards for adjusting the “sense amp” levels on sensors. Don’t let the technical term “sense amp” throw you, it simply means sensitivity.
Three factors decide correct exposure: ISO setting, f/stop setting and shutter speed. Like f/stop and shutter speed, discussed in Part 2, ISO settings come in standard values as shown below:
100, 200, 400, 800, 1600, 3200, 6400, 12800
Some cameras may eventually go much higher than ISO 12800, but for now it is pretty much a useless setting save for emergencies. There are two things that should be obvious from this progression of numbers. First, each one is twice the previous in numerical value. Second, this doubling/halving relationship is very much like shutter speed and f/stop full steps. This is not a coincidence. As you go up in ISO, each step in value requires half the light for correct exposure as the previous value, and just the opposite as you go down. So for any lighting condition there is a very large combination of ISO, f/stop and shutter speed that will satisfy exposure. The photographer chooses different combinations depending on the artistic effect he or she is trying to produce in a print.
As woodworkers we will opt for ISO 100, 200 or 400 combined with a small aperture and long shutter speed. The low ISO ensures little noise or grain in the picture, the small aperture produces large DOF and the long shutter speed is the price we pay, the latter mitigated with the use of a tripod.
Like 35mm SLRs, DSLRs come with a rich set of exposure modes. My Canon 40D has the following:
- Portrait, Landscape, Close-up, Sports, Night Portrait, Flash Off
- P, Tv, Av, M & A-DEP
- Three Custom Modes C1, C2 & C3
Group 1. is called Image Zone or Non-Creative Zone meaning they are pretty much fully automatic. The photographer trusts the camera to produce a reasonable result. Group 3. can also be fully automatic but the photographer has a say in many of the settings, but not at the time of image capture. Group 2. is the creative modes or zones. P stands for Program Auto Exposure, Tv for shutter priority, Av for aperture priority, M for manual and A-DEP for automatic DOF.
We are interested in Av, M and A-DEP. Av allows you to choose an aperture setting and ISO manually. It then determines the correct shutter speed. Aperture priority means you give priority to the aperture and let the automatic exposure system choose a corresponding shutter speed. Of course, if you want to choose all three manually (aperture, shutter and ISO) you can use M. As mentioned before A-DEP, a sort of DOF priority mode, chooses both f/stop and shutter automatically, but gives priority to DOF. The internal microprocessor evaluates the scene and adjusts f/stop until nearly the entire scène is in focus. Then it chooses an appropriate shutter speed. Focusing in any of these three modes can be either automatic or manual and can be achieved through the viewfinder or LCD providing your camera supports it.
File Format or JPEG vs. RAW
No matter what kind of photography I am doing, woodworking or any other, I always shoot RAW. Professional photographers will argue that this is wasteful in terms of file storage, development time, and even capture time if you are shooting sports scenes. But I am not a professional photographer, I am an adult, and I can shoot the way I want. Besides, I think I have good reasons to do so. First, let’s discuss what JPEG and RAW are. Every time you snap a picture with a DSLR an internal microprocessor captures information from the light sensitive sensor (electronic film), manipulates that information according to a number of algorithms and finally stores it on a memory chip according to some file structure. Common file structures are TIFF, JPEG, RAW, and many others I won’t mention here. RAW is actually a general classification of file types specified by each camera manufacturer. For example Canon uses .CRW and .CR2, Nikon’s RAW file is .NEF and Panasonic actually uses .RAW. There is only one quasi RAW standard and that is Adobe’s .DNG for digital negative. Adobe can take almost any RAW format and convert it to a .DNG RAW format with no loss of data. Adobe hopes one day it will be accepted as a standard and will be supported by all cameras so that a conversion isn’t necessary. It hasn’t happened yet.
You can mentally classify each file type by whether it is a compressed file or not, and whether the compression algorithm used is lossy or lossless. Most file formats are compressed to some degree. This helps to reduce storage space and improve transport time. Some compression algorithms compress files a lot, even to the point they sacrifice image content and quality, provided the end result is not too discerning by the eye.
TIFF (Tagged Image File Format) is a compressed file using lossless algorithms. It is used widely in desktop publishing, page layout and faxing applications. Of the three formats it is usually the largest. Many DSLR support or once supported TIFF, but are now focusing (no pun intended) on JPEG and native RAW.
RAW is a lot like TIFF in that it is compressed but using lossless algorithms, that is, the entire image content is preserved. RAW is generally compressed more than TIFF and hence smaller. But while TIFF is a standard, as mentioned RAW is different for each camera manufacturer. Why is that? Well it is probably equal parts of proprietary advantage, and different sensor technologies. Too complex for this tutorial, maybe another time.
JPEG (Joint Photographic Experts Group), like its motion picture equivalent MPEG (you guessed it – Motion Picture Experts Group), is a highly compressed file using lossy techniques. Many DSLRs allow you to choose levels of compression, sacrificing picture quality even more for smaller file size, hence more pictures on a memory card.
In most DSLR cameras RAW files are 3 to 4 times larger than their JPEG equivalent (equivalent in resolution, not quality). This is why JPEG is so popular. But there are a number of drawbacks to JPEG. First, JPEGs are highly processed by the camera. That is, depending on the Image Zone, custom setting, white balance and exposure you choose, the internal microprocessor “develops” the picture for you and then produces a JPEG file. Once the picture is developed, the original information is thrown away by your camera. It is akin to developing 35mm film. Once you put it through the chemical baths and develop it, you can’t go back. If you developed it poorly, sorry, deal with it!
RAW on the other hand is like exposed, but undeveloped 35mm film, but better; it lasts forever. You can develop it with a computer application such as Adobe Lightroom, but the development is non-destructive; the original file is left intact so that you can develop it again with a different “formula”. Try that with 35mm film.
Now some will argue that you can take a JPEG file and redevelop it in Lightroom or some other application. Not so fast! That is akin to taking a processed 35mm film (already developed), copying it via camera or scanner, and then developing that picture into a JPEG. The result is two layers of lost data. The point is, once you loose the information a camera throws away after creating a JPEG, you can’t get it back.
How much information are we talking about? Well there are three types of loses. The first is due to the compression which is lossy. The second is due to the choice of file format. The third is due to the fact that we developed the image, which means we made choices, perhaps bad ones, about exposure, color, contrast etc.
The file format is a big information loss, as is the developing. JPEG images are made up of pixels, the number of which depends on the resolution, e.g 10 megapixels. Each pixel has a Red, Green and Blue channel, and each channel is 8 bits deep. A little binary arithmetic says that is 256 tone levels per channel. RAW images on the other hand, are also made up of pixels with a Red, Green and Blue channel. But RAW images, depending on the camera manufacturer and the model, have from 10 to 14 bits per channel going to 16. My Canon 40D has 14. Again, binary arithmetic tells us that is 16,385 tones per channel compared to 256. Now before you say “Oh my God! I can’t believe the difference.”, even I have to admit not all that difference is perceived. The eye is a logarithmic beast. For example, shining twice as much light on a subject is not perceived by the eye as twice as bright. None the less this is a huge difference especially when it comes to artifacts introduced when we adjust color, white balance, contrast etc.
How this plays out will become more clear when we discuss Adobe Lightroom and image development. In fact, I may break the Adobe Lightroom installment into two installments to cover RAW vs. JPEG in more detail. I really feel strongly about RAW.
The Sensor – Digital Film
Perhaps the most important part of a digital camera is its sensor, that small rectangular semiconductor chip that lies on the focal plane of the camera. That is where the lens focuses the image, it is where the light intensity and color are registered and it is where the ISO speed is determined. More important than all of that, it is where the quality of the image is determined. You may read a lot about CCD (charged couple devices) vs. CMOS (complimentary metal oxide semiconductor) sensors. Go ahead and read it for education purposes, but in today’s technology world, both produce extremely good sensors. If I had to guess, CMOS will probably dominate or even eliminate CCD in the end, if for no other reason than the research infrastructure and manufacturing equipment infrastructure heavily favors CMOS. But as I said, if you buy a DSLR from one of the big guys (Canon, Nikon, Sony, Panasonic etc.) trust them to make the choice in technology. They are good at it.
What you want to look for are reviews by people like Digital Photography Review (www.dpreview.com) focusing on image quality. These people do a good job of quantifying the objective aspects of image quality. That said, here are a few things you can evaluate when comparing sensors:
- Resolution – As stated earlier, 10 megapixel is probably more than you will need. If you go higher make sure the sensor is physically large enough to produce high quality images (more in a moment).
- Bit Depth – Ideally you want 16 bits per channel, but 10 is ok, 12 better and 14 is great. Bit Depth determines the resolution of the sense amplifiers that detect the light falling on the sensor.
- Sensor Dimensions – I am not talking about aspect ratio here. I mean the actual physical dimensions of the sensor. Other things being equal, bigger sensors, or more specifically, the larger the area per pixel of resolution, the better.
The second point above gets to the issue we discussed in the previous section on RAW vs. JPEG. We want a lot of tonal information in our RAW file. This will give us a lot of room to correct all kinds of problems in the final rendering without creating unwanted artifacts common when capturing only JPEG files. I will demonstrate this visually when we discuss RAW files and Adobe Lightroom further.
The first and third points above are similar in some respects. You know that you can purchase a 10 megapixel point-and-shoot camera for around $100. You will also spend about $1,000 for a 10 megapixel Canon 40D. What’s the difference? Well a lot of things including lens quality, body design, shutter speeds and quality, functionality etc. But one of the large differences is the physical dimensions of the sensor. Semiconductor real estate is very expensive. In point-and-shoot cameras the manufacturer can’t afford to use much of it. So the sensors are tiny. However, specs sell, so manufacturers have to offer a 10 megapixel specification, even for a $100 camera. The problem is that the area per pixel is very small, which means there isn’t much silicon (semiconductor) to sense light, hence low signal. However, that same small silicon can be heated more readily by surrounding circuits, hence more noise. This makes the Signal/Noise ratio low, not what you want for high quality images.
Higher end DSLRs use larger area chips to sense the same 10 megapixels. Hence large Signal/Noise ratios, producing higher quality images and higher ISOs. But even in high end DSLRs it is important that you compare square mm/megapixel. Here is an example:
- Canon Rebel XTi, 10 mp, 22.2 x 14.8mm sensor, 12 bit depth, 32.9 sq mm/mp, very good image quality
- Canon 40D, 10 mp, 22.2 x 14.8mm sensor, 14 bit depth, 32.9 sq mm/mp, great image quality
- Canon 50D, 15mp, 22.3 x 14.9mm sensor, 14 bit depth, 22.2 sq mm/mp, great image quality but not as good as the 40D, especially in the higher ISO ranges (see www.dpreview.com)
While there are a lot of other differences between these three cameras, there are two that distinguish them one from another. The move from the Rebel to the 40D had more to do with bit depth. While the sensors were the same size, they weren’t the same sensors. I suspect the processing technology was improved in addition to improvements in the sense amplifier technology. The image quality improved as one would expect.
The move from the 40D to the 50D was kind of like the point-and-shoot tradeoff we discussed. In order to keep manufacturing costs consistent with the price range the silicon cost needed to be the same, hence the die size remained essentially the same. But to compete on specification the resolution was increased a whooping 50%. The image quality was actually slightly less than the 40D (more noise), though only in the higher ISOs. One has to wonder if this was a good tradeoff. Do we really need 15 megapixels in essentially a serious amateur/entry level professional camera? Isn’t image quality improvements with each generation more important? Don’t get me wrong, the 50D is an excellent camera, Digital Photography Review gave it their highest rating. But perhaps it could have been even better.
The last subject in this long camera installment I want to discuss is exposure metering. Most digital cameras have several metering modes, typically Evaluative, Center Weighted and Spot. These modes may have different names in different brands and models, but generally there is one mode that averages the entire scene and makes an exposure decision, a mode that looks at perhaps 30% of the scene around the center and makes an exposure decision and a mode that measures between 2 – 3% at the center and makes an exposure decision.
Spot metering is great. It allows you to choose a specific spot in the scene, perhaps a highlight, and expose for it. You can sample some number of spots and decide for yourself a correct exposure. The point is that it gives you options. The other two modes are more difficult to work with in terms of sampling a specific point or area. That said, the metering system in most DSLRs is quite good these days, so if your camera doesn’t support spot metering it is not a crisis.
In summary, the important features of a digital camera, as far as we woodworkers are concerned, are SLR technology, the ability to set ISO, support for Av aperture priority, DOF priority is a plus, LCD focusing, support for RAW files, a quality sensor and spot metering. It is now time to break. I will see you again in Woodworkers And Digital Photography – Part 4 where we will discuss RAW in more depth, especially as it relates to developing images in Adobe Lightroom.