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2nd September 2009, 10:51 AM
#1
A question on CCD size
A mate of mine is into macro photography of bugs and plants and things. I found it quite fascinating and thought I might give it a go. The old Nikon Coolpix 5700 with its fold out viewfinder would be good for this I thought as I wouldn't need to roll around in the mud to use the viewfinder.
The camera my mate used was even older, I think a Canon Cybershot, the one that rotates in the middle and is I think less than 3 megapixels. as far as digital cameras go quite old technology.
Getting to the point and I may have mis-understood here. With macro you're looking at depth of field in milimetres. What he explained was that the small CCD in the old technology Canon meant he had better depth of field, all other things being equal than the larger CCD in the Nikon. Does this sound right ?
Along a similar vein. When comparing zoom lenses for particular cameras is the actual amount of 'zoom' when expressed in focal length misleading as it, the 'zoom', is also a function of the CCD size ?
Is this why you see the term '35mm equivalent' when rerering to focal length in some specs. Does this mean that I need to know the CCD size of a camera before I can compare the effect of lenses between cameras ?
Deano
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2nd September 2009, 12:16 PM
#2
Yes, the larger the sensor, the more shallow the depth of field. This is one of the reasons why the Canon 5D with it's full frame sensor has such a 'cinematic look' compared to a normal handicam with a small sensor. It's also why little P&S type cameras all boast very capable macro modes.
Also you shouldn't think of it as the smaller sensor zooming the lens. You should think of it as cropping the picture. Granted for a 50mm lens, an APS-C camera will have the equivalent angle of view as a 75mm lens on a full frame (35mm film) camera, but the actual focal length doesn't change. The aperture is calculated as focal length / diameter, neither which change because of the sensor.
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2nd September 2009, 06:45 PM
#3
Werdan has provided a very practical and useful explanation, and that’s probably all you need to know. However if I'm allowed to be a bit anal, I'd add that depth of field is not a specific characteristic of the CCD. And if you dig into the math’s you will find many if's, but's and maybe's. Depth of field is not an exact thing. Some of the parameters involved include focal length, sensor size, detector size and fill factor (gaps between detector sights), and of course the circle of confusion (focus, diffraction and aberrations). However the way technology has evolved, most of these parameters have evolved together in such a way that in practical terms Werdan's advice cannot be faulted.
Also 'zoom' is a word exploited by manufacturers. Again it's a system characteristic that can be thought of as magnification, or the ratio of focal lengths, not the absolute lengths, and hence is independant of sensor size.
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2nd September 2009, 09:49 PM
#4
Perhaps 'angle of view' might be a better way of putting it ?
Deano
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11th September 2009, 01:21 PM
#5
depth of field
Let's get some facts right on optics.
Depth of field is determined by 2 basic things: focal length of the lens, and the aperture set on the lens.
A wide angle lens will have a greater depth of field than telephoto lens when used at the same distance from the subject.
For any given lens the depth of field will be increased as the aperture is stopped down. eg. f4 to f5.6.
Most lenses have an optimum aperture, usually 2 stops down that will give the sharpest image across the entire frame.
All lenses have what is known as a hyperfocal distance.
When focused on the hyperfocal distance the depth of field will be from half the hyperfocal distance to infinity.
Regards,
Peter. BA Ph, DipPh.
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