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Canon EOS D30 Digital SLR

Canon's first digital SLR packs 3 megapixels of CMOS sensor into a speedy, compact body! (Smallest/lightest digital SLR as of August, 2000)

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Page 3:Internal Design(!)

Review First Posted: 8/27/2000

Internal Design(!)
We're indebted to Canon USA, Inc. for the following series of photos of the internals of the D30. They reveal some interesting aspects of the camera's design and operation, and hold intriguing possibilities for the future...

First and foremost, a key factor in the D30's design is that it isn't just a modification of an existing film body: It was designed from the ground up to be a digital SLR, which is a significant part of why Canon was able to make it so compact: Not having to dedicate space to the usual film transport and focal plane mechanism, the designers were able to save considerable space. The diagram below shows a schematic illustration of the D30's body in cross-section. You can see from the way the components are stacked that it would have required much more space for the engineers to simply have tacked electronic components onto a film camera's body.

The illustration below expands on the cross-section above, showing how light passes through the D30's body to both the autofocus and flash sensors. As shown by the red lines, autofocus happens by virtue of a partially transmissive region in the middle of the main mirror. A secondary mirror reflects the light down to the base of the camera body, where it passes through a lens, reflects from yet another mirror, and thence into the AF sensor itself. Focusing can thus be continuous right up until the mirror flips up for the exposure itself.

The TTL (through the lens) flash sensor resides at the top of the camera, behind the pentaprism. Here, a small mirror and lens pick off a portion of the light passing to the viewfinder. (Note that this is before the focusing elements of the viewfinder optics, so it achieves more area coverage than you might expect.) The light reflects from a mirror, passes through a lens, and thence to the photodiode that measures returning flash energy. This design requires a pre-flash for metering, but is the same system used by other EOS cameras. This means that all EOS-compatible Canon flash units will be fully functional with the EOS D30. This approach also avoids the difficulties inherent in adapting camera designs based on Off-The-Film (OTF) flash metering. The disadvantage is that the metering occurs a small fraction of a second before the shutter opens. The strong advantage though is that it alleviates problems relating to differences between sensor and film reflectivity. (We found the flash metering of the D30 to be exceptionally accurate.)

The real "guts" of the D30 is a cast plastic optical box holding the lens mount on the front, the pentaprism on top, and the CMOS image sensor on the rear. This compact arrangement is a major factor in the small profile and light weight of the D30 overall.

Here's a look at the D30's optical box from the back, revealing several interesting features, as detailed in the photo's caption:

Overall, modularity seems to be a key word in the design of the D30: Canon's engineers obviously weren't designing with one camera in mind, but an entire family. In our conversations with them, Canon USA's technical folks made much of the component shown in the photo below, the "Engine" that handles the D30's image processing. Again, note our comments in the photo caption below.

The shot below shows both why the D30 has a very rigid, rugged "feel", but also part of why Canon themselves don't claim it to be a "professional" model. The body is composed of heavy gauge stamped metal: Very rugged and rigid, but clearly not in the same class as the die-cast body of the EOS-1V. Still, there's no doubt that this isn't a "plastic" camera!


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