The modes described here are for Canon cameras, equivalent or similar modes but with sometimes slightly different names are available on all modern DLSR cameras from major manufacturers.
The basic camera modes available are
P – Program. The camera selects aperture and shutter speed, and controls flash if a compatible ETTL flash is attached. Effectively turns a DSLR into a “point & shoot”, little value for creative photography.
Tv – Time Value commonly referred to as Shutter Priority. User sets the shutter speed and the camera calculates and sets the aperture.
Av -Aperture Value, commonly referred to as Aperture Priority. User sets the aperture and the camera calculates the appropriate shutter speed.
M – Manual Mode. User sets shutter speed and aperture. Allows the most creative control of the resulting image.
TV mode would be selected when you want to control the speed of the capture this could either be to ensure a very fast shutter speed e.g. bird in flight where you typically want all the image to be sharp or conversely to ensure a slower speed is used, perhaps, to introduce some “motion” into parts of the image.
AV mode is typically selected when you want precise control of the depth of field. e.g to ensure a landscape image is sharp from back to front, using a small aperture, or conversely to ensure a portrait photograph background is blurred by using a wide aperture.
M mode is when you want complete control of shutter speed and aperture. It is often useful to use TV or AV mode to meter with initially in order to give a starting point for manual settings and then adjust as you wish based on a combination of evaluating digital display and / or histogram. Taking multiple exposure can be automated using bracketing, the exposure variation can be set usually in 1/2 or 1/3 stops and the camera will take 3 sequential images. These can be one either side of the default exposure or all either darker or lighter.
Light Metering Modes
Canon Digital Cameras typically have 4 light metering modes.
Evaluative (Or pattern / matrix metering on other cameras) Camera divides sensor into zones and averages the value across the entire image, excellent for evenly lit subjects. On more advanced models “centers” the zones around the autofocus point selected assuming that is the area of the image that is most important. Is generally the default metering mode.
Centre weighted metering, similar principle to evaluative metering but gives more weight to the central area of the image, if the are of interest is not in the centre then use the exposure lock to meter the area required and then re-frame image.
Partial Metering , uses only a small area of the central view finder area (approx 10-15% of the entire sensor area) useful where there are large variations in the contrast across the image. E.g. backlit image where you want to ensure the foreground is visible, however this may result in background being over exposed or completely blown out.
Spot Metering similar to partial metering but uses an even smaller area of the sensor area (2-4%) to get a very precise reading of a small area of the image.
It is the combination of the camera mode and metering mode that determines the final image, spot metering is often used in combination with manual camera mode to provide precise control of exposure for certain areas of an image. e.g. a spot reading is taken in AV mode a meter reading and then the camera is set to the camera is set to the f-stop and shutter speed indicated.
TV mode would be selected when you want to control the speed of the capture this could either be to ensure a very fast shutter speed e.g. bird in flight where you typically want all the image to be sharp or to ensure a slower speed is used perhaps to introduce some “motion” into parts of the image.
The racing car image below was taken in TV mode at 1/800th – slow enough to have some blur on the rotating wheels but combined with panning (following the motion of the car) whilst shooting then the static parts of the car are sharp, the background is blurred due to the panning motion rather than the aperture. Evaluative metering selected as little contrast in the image i.e. even lighting.
The daffodil image was taken in AV mode as I wanted to ensure the background was out of focus and thus limited the depth of field to the nearest daffodil heads. If the background was brighter it might have been necessary to meter for the background exposure and use fill in flash to illuminate the front of the daffodils but on this occasion it wasn’t necessary. Centre weighted metering on the daffodil heads. F7.1 1/640th
In the landscape image below a sharp depth of field was required from front to back of the image so a small aperture of F22 was selected and the focus point was the cactus about 1/3 into the image. Even though a bright day the aperture at F22 meant a 1/6th shutter speed and hence use of a tripod to eliminate any camera shake. Evaluative metering.
For the night shot of the pier full depth of field was required in addition to a lengthy exposure due to the low light conditions. F 16 at 30s seconds making use of a tripod essential to obtain a sharp image, centre weighted metering on the darker part of the image with exposure lock. Some burning of the sky in post processing.
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