The future of digital SLRs

August 5th, 2008 - 06:04:26 AM:

(Update from August 5th, 2008)

Currently DSLR design still concentrates on packing more pixels onto the sensor and adding features to the camera firmware. As the megapixel race continues, however, it becomes more and more pointless. Most lenses can not resolve enough detail to require tens of megapixels, and sloppy technique often prevents that both lenses and sensors are used to their full potential. So as there is a limit of information that reaches the sensor, there's no point to use more and more pixels to record it. Once the pixel number of the sensor is higher than the total resolving power of the lens-photographer system, there is no advantage of adding more pixels. Also, more and more people will realize that they don't need 20 megapixels even for full page magazine prints. The novelty value of ever larger numbers in sales brochures will soon fade out.

So efforts will shift towards other areas. Mid- and longterm there will be increased emphasis on quality, usability, and getting rid of the past. Let's start with my look into the crystal ball:

Mechanical shutters are on the way out

Current DSLRs use mechanical shutters just like film cameras. That's not because it's the best way to construct a camera. It's because the technology is available and mature, and current full-frame CCD technology requires the sensor to be covered while it's read out. More advanced sensor technology does no longer need a shutter (as seen from today's digicams), but image quality does not reach that of full-frame CCDs. So with the quality-aware buyers of DSLR, mechanical shutters are currently the right compromise.

However, I believe this will change. Sensor technology will improve to the point that image quality can be retained even without a mechanical shutter. Then there's no longer a need to use shutters. This will all of a sudden improve the system significantly:

  • Shutters are high-precision mechanical parts. Or in other words, they are expensive. The money you save on shutters can be used better elsewhere.
  • Shutters are slow. That's why SLRs have a flash x-sync speed that's significantly slower than their shortest exposure time. When you want to use flash at shorter exposure times, you have to use tricks like FP-sync flash or HSS. Without a shutter, none of these tricks are needed. You can use regular flash at full power up to the shortest exposure time. Again, more money to spend on something else.
  • Shutters create noise and vibrations.
  • Shutters sometimes fail. Without shutters you have fewer mechanical parts that can fail.

In future DSLRs there may be a simpler, slower, mechanical shutter that is only used to cover the sensor while you change lenses. But even this may be obsoleted (see below).

Oops, it's not a SLR anymore!

DSLRs still carry a lot of technology from old film cameras, namely the mirror, matte screen, prism and optical viewfinder. Again, this is not because it's the best way to build a camera. It's because the technology is available and mature. Looking at digicams again, you can see that you can build a digital camera without all that, using electronic viewfinders. But again, current technology is not up to the quality requirements of typical SLR buyers, so carrying over old camera technology is the right compromise at this time.

Again, I think this will change. Sensors will be improved to allow readout at high frame rates and at a lower resolution, and display technology will be improved with regard to resolution, speed and dynamic range. This will lead to electronic viewfinders that are just as good as current optical viewfinders. You will no longer need a mirror, matte screen and prism.

Throwing out old stuff can be liberating. Using electronic viewfinders will have the following advantages:

  • The viewfinder no longer needs to be tightly coupled to the camera. It can be tilted up, swiveled and maybe even detached from the camera. You will never need an angle finder again. Alternatively, you can shoot tethered in a studio, using a large computer screen as a viewfinder.
  • Viewfinder image and final image will never be out of sync. They are both taken by the same image sensor. It'll be easy to provide a 100% crop of the image in the viewfinder instead of the current 90-something percent.
  • You have more freedom to manipulate the viewfinder image. Current optical viewfinders offer only a LCD status line and a few highlighted spots in the image area. With electronic viewfinders you can overlay the image with whatever you want. You can see a live histogram, important status messages etc., and the viewfinder image can be automatically displayed brighter when you use DOF preview to compensate for the light loss caused by the closed aperture. You can zoom into parts of the image for precise manual focusing. No need for an extra viewfinder loupe! You will always have a bright viewfinder image even when there is little light.
  • You can record movies. Even advanced amateurs and even professionals may want to do this from time to time.
  • Again, less noise and vibrations from the flip-up mirror. No need for a special mirror lock-up function.
  • Again, fewer mechanical parts that may fail.

What you get will then be no longer a SLR in the literal meaning of the acronym. It will, however, still be a system camera, and it will look and feel like a SLR.

Of course, when you no longer have a mirror, you also no longer need to provide the space for it. Reducing lens registration (distance between image plane and lens mount) makes lens design easier, especially for wide-angle lenses. However, changing the lens mount would also mean that you have to buy new lenses. If you have thousands or even tens of thousands of dollars invested in your lenses, this is likely something that you don't want to do. So camera makers may keep the lens mount unchanged and use the available space for something else. For example, they may insert a protective glass into the space between lens and sensor. Dust would settle on the glass instead of the sensor, far away from the image plane and thus practically invisible. This would also make a protective shutter unnecessary.

Alternatively, makers may offer new lenses for a shorter registration distance, and a special extension tube to be able to use also old lenses that are designed for the longer registration distance.

There's one disadvantage. Without the flip-up mirror, it's no longer possible to use phase detection AF sensors as we know them today in SLRs. Camera makers will have to work hard to improve video AF to a level equal to today's phase detection AF.

Storage media

Today's storage media are the bottleneck of the recording system. The write speed of today's NAND flash can not keep up with the increasing data rate from the sensor. So today's DSLRs need megabytes of image buffers so that at least a few images can be recorded at full speed before the camera has to slow down to write these images to the storage medium. These megabytes of RAM cost money and require power to operate, something that can be used better for other things (like electronic viewfinders). Future storage media will still use common formats like CompactFlash, SD card, Memory Stick, etc., but the technology inside will be something faster.

CPUs help lenses

Future lenses will provide additional information to the camera, for example their level of distortion and vignetting. While it's still best to optimize sharpness and chromatic aberrations in the lens, other things can more easily (and cheaper!) be corrected by the camera. So lens design compromises may shift towards sharpness and chromatic aberrations and away from distortions and vignetting, still yielding better overall results. For old lenses, the camera may either apply no corrections (gaining nothing, but also losing nothing), or cameras may be equipped with a database containing these parameters for older lenses.

Image quality

Sensor technology will concentrate more on improving dynamic range, color rendition and general image quality than on cramming ever more pixels on the same space. Photographers will probably profit most from increased dynamic range, which is one of the more problematic areas of current sensors. The Fuji sensors hint towards what we'll see in the future.

Color accuracy will also be improved. There are already sensors recording four colors instead of three, and this is something that we may see more often.

There's also still room to improve efficiency of current sensors, in terms of sensitivity, S/N ratio, and chip area usage. These improvements can all be done without making chips bigger, i.e. without making them more expensive.


Update from August 5th, 2008

Obviously Olympus and Panasonic have started making the changes described above. They have announced their Micro Four Thirds lens mount, which basically has all the above characteristics:

  • No mirror
  • Half the registration distance
  • Contrast detection AF
  • Electronic viewfinder
  • Movie recording
  • Can use old lenses with adapter

It remains to be seen how the new system will be realized in actual products, especially with regard to the quality of the AF system and the viewfinder. Also, the advantages for lens design will only be seen with new native lenses, not with adapted legacy lenses.

For details see the Four Thirds home page