HIGHER AND LOWER SENSITIVITY
A camera's sensitivity to light is measured by its ISO( International Standards Orgaanisation).It goes that the higher the sensitivity to light, the faster the shutter speed required. If you switch on the camera and set it to ISO 3000 example , you need a shutter speed and focal length that will balance out the light meter. A slow shutter speed like 4 seconds will allow too much light on to the sensor while a fast shutter speed will allow little light to pass through the sensor. A higher ISO reading is generally used in darker situations to get faster shutter speeds while a lower ISO reading gives us shots with less grain or noise since we are able to open up the aperture wide with less shutter speeds.
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| Image 1: ISO 320 ,50MM,F/5,1/640 |
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| Image 2:ISO 800,50MM,F/5,1/1600 |
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| IMAGE 3: ISO 2000,50MM,F/5,1/4000 |
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| Image 4: ISO 4000,50MM, F/5,1/8000 |
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| Image 5:ISO 6400,50MM,F/6.3,1/8000 |
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| Image 6: ISO 25600,50MM,F/13,1/5000 |
In the Images above, the lowest ISO used is 320 while the highest is ISO 25600. As seen, image no 6 is quite grainy. These shots were taken on a bright overcast day. I realised that setting the camera at higher ISO made it easier to snap a picture because the sensor is more sensitive to light and shutter speed has increased.
Bryan Peterson explains the concept further in page 20 of his book "Understanding exposures", Third Edition.He likens ISO to a worker bee. If a camera is set for ISO 100, in effect there are 100 worker bees and another one set for ISO 200 has 200 worker bees. The job of the worker bees is to gather the light that comes through the lens and make an image. If both lenses are set at the same aperture such that the same volume of light will be coming through the lenses, ISO 200 will record the image quickest since it has twice as many worker bees than ISO 100.
These days, a camera.s ISO ability is part of its selling price determinants, others being frames per second,build quality, and shutter actuations. Called low-light ability, some cameras are able to produce great details even when the ISO is set to high limits where you will expect to see grainy images in other lower camera's. Camera's like the Nikon D4 can produce usable pictures at ISO up 12500.
Image 7 Windstorm:ISO 25600, 70MM,F/25,1/50,notice the graininess at high ISO.
Depending on what a picture will be used for, noise or graininess may or may not matter. I would think that in photo journalism, the photographer will want to go for the decisive moment, in the way of Henri-Cartier bresson. That may not get him to prioritise picture clarity. But a fashion and modelling photographer will care a lot about picture clarity.
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| Image 8:ISO 1000,50MM,F/1.4,1/10 |
In Image 8 above shot in one of the streets of London, used an ISO of 1000 and a low shutter speed of 1/10. But observe that the lens was wide open at f/1.4 implying a very shallow depth of field. No flash was used and as seen, the image is not grainy at ISO 1000. Images generally start degrading above ISO 1600 in APC-S sensor camera's.A mid range Nikon D7000 camera was used for this image.
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| Image 9:ISO 500,70MM,0EV,F/7.1,1/25 |
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| Image 10:ISO 2500,70MM,0EV,F7.1,1/40 |
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| Image 11:ISO 6400,70MM,0EV,F7.1,1/5 |
Images 9 to 11 were taken in my study area at home further explaining ISO. It was much easier taking the second picture Image no 10 when i increased the ISO to 2500, with the shutter speed increasing to 1/40s. As I was about clicking away the third shot, there was power failure with only the blacberry illuminating the room. I cranked up the ISO to 6400 which dropped my shutter speed to 1/5s. A closer examination of this image will reveal a lot of grain.
MY THOUGHTS
Recently I have not been making as much progress as i would like on my OCA exercises lke i have oft mentioned due to work. But I set myself to it. As I was getting set last week to continue, my macbook pro hard disk crashed and i had to take it for repairs. Thankfully I was able to get it back in shape within two days and with my data backed up, there was,nt much problems after wards retrieving information.
I have also been spending a lot of time on the internet researching the works of wildlife photographers. I find myself drawn to this genre of photography admiring the works of bird photographer arthur morris and wildlife photographer moose petersen. In the UK , richard peters is also one heck of good wildlife photographer. I think two major reasons stand out for my interest in wildlife photography. Love of nature and not needing an animals permission before you photograph it. You only need to be very careful approaching wild animals. Another reason why i like nature photography is conservation. I believe photography has an important role to play in bringing to the fore conservation issues such as wildlife protection and preservation of flora and fauna.
Wildlife Photography by Uwe Skrzypczak is one book i have read lately and i truly enjoyed images of the big cats , some of which are quite humorous. I am presently making arrangements for a photo safari to Tanzania sometime in mid 2014. Images of the serengeti have stuck in my memory since childhood and i would like to see in reality. In wildlife photography, the best time to photograph animals is in the golden lights period from 6.30 to 9.00am and in the evenings from 4.30 to 6.00pm. By the time am going to tanzania , i should be in my second course module people and places.
