With the imminent arrival of Canon's EOS 1Ds MIII and Nikon's D3, both full-frame 36x24mm. image formats, it's worth having a look at the pro's and con's of full-frame digital capture.
With smaller formats the only way to improve image quality is to cram in more and more smaller pixels resulting in 'noisier' chips partly negating the improved image.
So one cannot deny the advantages of a larger sensor - more pixels without the noise = better image quality, except that Nikon have opted for a 12.1 mega pixel sensor and seems to be designed for faster work flow and shooting rates whereas, Canon's massive 21.1 mega pixel sensor can produce files well in excess of the quality requirements of top Image Libraries.
Another great advantage of a larger format is a larger, clearer, viewfinder image making focusing so much easier and by comparison makes the D2x or D200 or APS format viewfinders positively dull as the smaller screen and mirror transmit less light causing the manufacturers to utilize focusing screens with very little 'ground glass keying' effect, virtually clear in fact, so difficult to focus precisely and quickly.
That's the good stuff, there are however some not so good aspects that are not immeadiately apparent.
It would be logical to think that all 35mm. format designed lenses would be compatible with a full-frame digital sensor and that you could save a pile of cash by dusting off all your old lenses and sticking them on the new camera and, yes, the covering power or image circle projected by those lenses is adequate. You may well have used these lenses on smaller format digital sensors and got great results but you didn't see the image quality at the image edges because the small sensor didn't utilize that part of the image - cropped out in effect by the small sensor. Applying these lenses to full-frame may reveal some unwanted fuzzyness at the image edge especially with wide-angle lenses.
CCD sensors are not happy with light rays coming at them from an oblique angle. They are prone to Chromatic Abberations similar to a lens's inability to resolve differing wavelengths of light at exactly the same place. Unlike film, which can cope with steep incident light rays arriving at the image edges, digital sensors perform best when light arrives straight on, close to 90 degrees to it. To achieve this the lens must project it's image on a light path that is, or as near as possible, parallel to the lens axis. The lenses that can do this are of a 'Telecentric' design having a large exit pupil with a diameter almost as great as the diagonal measurement of the sensor format and on smaller format sensors work very well at optimising the image quality.
In pursuit of optical perfection then, if the sensor prefers straight on light rays, a telecentric lens design is needed which in turn needs a larger lens flange which would require the camera to have a lens mount or throat equal to that on Pentax 67.
These lenses would be huge, heavy and expensive especially so with 'Anti Camera Shake' technology built in as both Nikon and Canon lenses have as opposed to 'Sensor Shake' technology that enables the sensor to move in tandem with percieved shake that full-frame cannot permit because the sensor would move outside it's image circle.
So what's the answer? The conclusion is not to use older lenses on these new cameras but buy dedicated versions and this really means investing in a whole new bag of kit - again.
Having said all this it's good to see Canon and Nikon pushing at the walls of possibility!
Here is the problem. The diagonal of a full-frame sensor is 43.2mm. The limiting factor against telecentric lenses is therefore the lens mount.
To enable older lenses to fit, Nikon still uses it's 45mm. diameter lens flange and Canon has it's 48mm. equivalent, no where near large enough to house the glass elements needed to project an image of 43.2mm. in diameter.
This dilemma is oddly reminiscent of camera manufacturures problems years ago that could not accept the new retofocus wide-angle lenses that where then becoming popular. Nikon, Canon, Leica et al where all fortunate in having large 'throats' for their lenses enabling them to prosper whereas many other camera marques died.
A secondary problem with utilizing lenses designed for film is the 'Circle of Confusion', lens manufacturers jargon for the tiny discs of light that form an image, that film was also happy with. This Circle of Confusion must not be greater than the space between one pixel and the next otherwise resolving power is poor. Lenses designed for CCD sensors have improved resolving power to combat this.
Lens Mount or Throat
on the New Canon
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