Lesser Aperture means greater DOF
Ability to maintain acceptable sharpness on nearer and farther objects at same time in same photo is DOF. Shorter the aperture more sharper the farther objects will be in addition to object at current focus.
While this is enough to play with camera, for the curious: read more here.
Tuesday, November 20, 2007
Lesson Three: ISO, Grain and Noise
For lesser noise keep ISO levels as less as possible
ISO level 100 is considered normal and it goes like 200, 400 etc. Higher ISO level means faster films. Faste films mean that amount of light to be collected is not high because you have sacrificed lesser noise for speed. That is you can have faster shutter speeds, lower apertures in dark light, ofcourse you will have higher noise in the picture.
In circumstances like a sports photo in a dark lighting would you want to get higher shutter speeds to freeze shots of a moving object. And you would achieve this by bumping up the ISO.
Grain is the word from film days and finer grain is associated with lower ISO or less sensitive films. By less sensitive means lesser sensitivity to external light.
So, now, we have another parameter added to exposure equation.
Read more here
and here
ISO level 100 is considered normal and it goes like 200, 400 etc. Higher ISO level means faster films. Faste films mean that amount of light to be collected is not high because you have sacrificed lesser noise for speed. That is you can have faster shutter speeds, lower apertures in dark light, ofcourse you will have higher noise in the picture.
In circumstances like a sports photo in a dark lighting would you want to get higher shutter speeds to freeze shots of a moving object. And you would achieve this by bumping up the ISO.
Grain is the word from film days and finer grain is associated with lower ISO or less sensitive films. By less sensitive means lesser sensitivity to external light.
So, now, we have another parameter added to exposure equation.
Read more here
and here
Monday, November 19, 2007
Lesson Two: Playing with stops
If amount of light collected (similar to water in balloon model) in a setting is x.
If we collect twice of that, 2x then we say we have moved a stop.
We can move stops in exposure by moving up on aperture stops or shutter speed. Shutter speed stops are very simple, from current setting of, say, 1 second you have to go to 2 second. That is double the time. For aperture stops it is not the radius but the area which should double. Since area is proportional to radius square i.e. radius*radius, radius should move by square-root(2) i.e. 1.414. And then couple this with unintuitive F number (which is inverse of radius). For aperture to go up by a spot, the F-number should go down by 1.414.
Best way to try this to use Aperture Priority or Shutter Priority modes, where camera allows one of the aperture or shutter speed to vary and other is fixed to get normal exposure. Change one and see other changing by equivalent amount in other direction.
If we collect twice of that, 2x then we say we have moved a stop.
We can move stops in exposure by moving up on aperture stops or shutter speed. Shutter speed stops are very simple, from current setting of, say, 1 second you have to go to 2 second. That is double the time. For aperture stops it is not the radius but the area which should double. Since area is proportional to radius square i.e. radius*radius, radius should move by square-root(2) i.e. 1.414. And then couple this with unintuitive F number (which is inverse of radius). For aperture to go up by a spot, the F-number should go down by 1.414.
Best way to try this to use Aperture Priority or Shutter Priority modes, where camera allows one of the aperture or shutter speed to vary and other is fixed to get normal exposure. Change one and see other changing by equivalent amount in other direction.
First lesson : collecting light
Water Balloon Model
Imagine that you have balloon filled with water. You pierce a hole in it and collect water in a glass. Now three things decide how much water you collect,
1. The size of the hole you pierce
2. The time for which you collect
3. The speed with which water flows, which depends on amount of water in balloon (pressure).
In photography too, the first step is to learn to collect enough light, or say photons. In daylight photography, (3) is given to you. Depending on the time of day, clouds, Sun etc. the intensity of light is given. You are allowed to vary (1) and (2).
In photography terms used are,
Exposure: Amount of light collected
Aperture: Size of hole you pierce
Shutter speed: Time of collection
Now, accept some of weirdness in naming, units of selection. Shutter speed is measured not in terms of speed but time units. If your camera shows a shutter speed 25, that means 1/25s (one-twenty fifth of a second) is the time for which shutter is open. But if it says 3"5, it means 3.5 seconds- wierd:-), just look for presence or abscence of ".
Aperture should ideally be measured in terms of radius of opening, but it is inverse - weird :-), stay on to find more funny things. So apertures are measured in terms of F-number. A F-number of 5.6 is more open compared to 22. So F-number is 1/radius.
And these things are measured in stops. So u can give stops in apertures and take apertures and get the same exposure. So down two stops in aperture (make the hole smaller) and go up two stops in shutter speed (make the time larger) and you get same exposure.
Exposure doesn't have units, its measured in stops. So you say exposure is normal, or two stops under or two stops over.
And it is not enough to know these, it should go into permanent memory as numbers in maths have gone into. If you cannot follow these then you cannot follow any photography discussion.
Revise this lesson with better visuals here.
Imagine that you have balloon filled with water. You pierce a hole in it and collect water in a glass. Now three things decide how much water you collect,
1. The size of the hole you pierce
2. The time for which you collect
3. The speed with which water flows, which depends on amount of water in balloon (pressure).
In photography too, the first step is to learn to collect enough light, or say photons. In daylight photography, (3) is given to you. Depending on the time of day, clouds, Sun etc. the intensity of light is given. You are allowed to vary (1) and (2).
In photography terms used are,
Exposure: Amount of light collected
Aperture: Size of hole you pierce
Shutter speed: Time of collection
Now, accept some of weirdness in naming, units of selection. Shutter speed is measured not in terms of speed but time units. If your camera shows a shutter speed 25, that means 1/25s (one-twenty fifth of a second) is the time for which shutter is open. But if it says 3"5, it means 3.5 seconds- wierd:-), just look for presence or abscence of ".
Aperture should ideally be measured in terms of radius of opening, but it is inverse - weird :-), stay on to find more funny things. So apertures are measured in terms of F-number. A F-number of 5.6 is more open compared to 22. So F-number is 1/radius.
And these things are measured in stops. So u can give stops in apertures and take apertures and get the same exposure. So down two stops in aperture (make the hole smaller) and go up two stops in shutter speed (make the time larger) and you get same exposure.
Exposure doesn't have units, its measured in stops. So you say exposure is normal, or two stops under or two stops over.
And it is not enough to know these, it should go into permanent memory as numbers in maths have gone into. If you cannot follow these then you cannot follow any photography discussion.
Revise this lesson with better visuals here.
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