ADAM Technology is often asked to recommend a camera to use with 3DM Analyst. This page makes a few general recommendations while attempting to explain some of the important points that should be considered.
The software itself will work with images from any digital camera, as well as images from metric film cameras that have been scanned with a high-quality scanner. The results that can be obtained vary depending on the characteristics of the camera used.
The first characteristic of digital cameras that everyone looks at is the number of pixels that it produces. While this is an important measure, it is by no means the whole story.
Another important measure is the actual size of the pixels in the image sensor. Image sensors are made in much the same way as computer chips, and the rules that apply there — smaller means cheaper — apply to image sensors as well.
This means that it is much cheaper to manufacture a 12mm × 8mm image sensor containing 6 million pixels, each 4 microns in size, than it is to manufacture a 24mm × 16mm sensor containing 6 million pixels, each 8 microns in size.
The problem with these small sensors is twofold:
The optical resolution of the camera's lens system is unlikely to be high enough to provide the detail that would make 4 micron pixels worthwhile. Making the pixels smaller than the lens' resolution doesn't increase the amount of detail in the image, the image just gets blurrier. Pixels below about 7 microns need a very good lens indeed.
Pixels in image sensors convert light (photons) into electric charge (electrons) during exposure. A greater charge capacity in a pixel means a greater signal-to-noise ratio, or lower noise in the image. Since the charge capacity of a pixel is proportional to its area, an 8 micron pixel has four times the charge capacity of a 4 micron pixel, or one quarter the noise.
From the point of view of 3DM Analyst, the first problem simply means the image contains more pixels than it really needed to for the information it contains. This is not really a problem, but it does mean that not all 6 megapixel images are created equally and you need to keep this in mind when choosing a camera. The second problem is potentially more serious — noise in the image directly affects 3DM Analyst's ability to recognise the same point in both images, reducing the likelihood that it will correctly identify a common point, and increasing the likelihood that different points will be incorrectly matched.
Which cameras use the larger image sensors? Generally speaking, consumer-grade compact cameras do not — they tend to save manufacturing costs by using small sensors with tiny pixels. The cameras that do use these larger sensors are the Digital SLRs. The cheapest ones are actually cheaper than the most expensive compact cameras, and they have the added advantage of being able to exchange lenses to make them more flexible in use.
Digital SLRs are currently the best readily-available digital cameras to use with 3DM Analyst. The highest resolutions are around 21 megapixels with 36mm by 24mm image sensors, and with each pixel about 6.4 microns in size. Cameras with 12 megapixels are in the same price range as the high end consumer cameras.
The cheapest of the current crop are the Canon EOS 450D and the Nikon D60. Both are over 10 megapixels, and both are available for less than A$1,000 in Australia. The best digital SLR as of 2008 is the Canon EOS-1Ds Mark III (21 megapixels, for around A$11,000).
Despite their shortcomings, there is nothing to stop you from using a consumer-grade compact digital camera with 3DM Analyst. ADAM now uses a Canon EOS-5D for demonstrating the software, but previously we used a 3 megapixel Ricoh RCD-7 with tiny, 3.6 micron pixels, and before that we used a 2 megapixel Nikon Coolpix 800. The small pixel sizes of these cameras meant they suffered from noise and slightly blurry images, but 3DM Analyst coped well. Keep in mind, however, that the extra cost of a better camera may be justified when you look at the total costs of the system.
The Digital Photogrammetry Review website is a great place to look for camera reviews and more detailed explanations of the technology. All of the cameras mentioned above are reviewed there, and many more besides.
If you wish to use images taken by a film camera with 3DM Analyst, you have two options: scan the images, or purchase a digital back for your camera.
While consumer-grade scanners are very cheap and easy to obtain, they generally do not have the geometric accuracy needed to get the best results with 3DM Analyst. To really compete with a high-end digital camera, a photogrammetric scanner like ADAM's own PROMAP ORTHO System 2 is required. (See the Model 1 project on the Samples Projects page for an example.) Unfortunately, photogrammetric scanners are very expensive — several times more expensive than the most expensive digital SLRs — and thus can only be justified when used with large format (230mm) film cameras, which typically run into the many hundreds-of-thousands or even millions of dollars themselves. Unless you have one of these cameras (in which case you need 3DM Analyst Professional) or there is a scanning bureau nearby, it is probably better to go with a digital camera. Not only will this save the cost of scanning, but it will also give you all of the other advantages of digital photography as well — instant turnaround, no film costs, no development costs, etc.
The highest resolution digital cameras available (excluding large format cameras in the million-dollar range) are the digital backs that can be purchased for medium format film cameras. As of 2008 the largest of these are 39 megapixels.
If you already own a medium format film camera, these options are worth considering. 3DM Analyst works fine with them — the Freeport project on the Samples Projects page was taken with a MFDC Hasselblad 555 ELD camera using a 16 megapixel digital back. It would be worth remembering the cost associated with these, however, and comparing the results with the top-of-the-range digital SLRs before buying.