# DSLR basics: Shutter.



## Gruffs (Dec 10, 2007)

*DSLR basics:*

Right,

This is meant to be a short series of guides to the basics of DSLR usage and the different parameters that can be adjusted to change and/or manipulate and image. Some of it may well be applicable to Compact cameras too.

So, you've pointed your camera at the thing you want to photograph, What happens and what must you do to get a 'good' image?

All the camera does is projects an image that you have pointed it at onto the sensor. That is all. You can adjust how the camera does this to get different effects.

So we'll start with Shutter speed;

The Camera has a lens, a mirror and a shutter in front of the Sensor. As you point the camera at the scene, the lens is focussing the light to a distance which is where the sensor sits. This is called the Focal or Image Plane. What the Shutter does is block or allow the light to 'hit' the sensor or specifically timed periods. The mirror deflects the image up and through a prism to the viewfinder (the image you look at). So when you press the button halfway, the Auto Focus (AF) and the Metering do their thing, the mirror flicks up and the shutter opens allowing a timed amount of light from the scene onto the shutter.

So all the shutter does is allow the light from the lens to hit the sensor for a specific amount of time. Usually displayed as a fraction of a second (1/100) for less than a second and decimal (1.5") for more than a second. Easier for the LCD I think.

So, the effect this has on an image;

If you imagine the lens as a hosepipe and the amount of light as a pump and light itself as water. To correctly fill a vessel (Exposure), you must allow the correct amount of water out of the hosepipe for that vessel. So, imagine the shutter as your trigger on your hosepipe.

So If the pump is turned up high (loads of light, well lit scene) then you will need to hold the hose open less time than you would if the pump is low (low light) to correctly fill your vessel (Correct Exposure).

So for Bright lighting conditions, You have a faster shutter speed. For less light, you have a slower shutter speed.

Now, varying shutter speed has an effect on technique too. If you have a low light situation, then you need your shutter open for longer to expose your image. But if you go wobbling the camera around during that exposure, then light meant for a certain pixel, hits a different pixel and you get blur. So you want to have enought light to allow a fast enough shutter speed to expose your image faster than any blur that you induce can mess it up. Or, You stop the wobble (tripod etc).

I'll continue this later on.

Can you experience guys have a read and PM me any corrections.


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## davies20 (Feb 22, 2009)

Gruffs said:


> Right,
> 
> *So for Bright lighting conditions, You have a slower shutter speed. For less light, you have a higher shutter speed.*


Is this not the other way round? Or am i reading it wrong. I thought it was....

Lots of light - Quick Shutter

Less light - slow shutter


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## bretti_kivi (Apr 22, 2008)

The statement goes like this: 
Bright light --> high shutter speed (1/1000s) with small apertures (f22)
Dim light --> low shutter speed (1s) with large apertures (f2.8)

Another thing to take into account is that the light can and should also affect your ISO settings, which then affect your aperture decisions (which should be affected by your depth of focus field considerations). 

Remember, also, that if you try to capture a fountain at 1/8000, you will get a lot of water drops and no longer a continuous stream.

Following on from this: if you're photographing a moving vehicle and want it to look like it's moving, consider speeds around 1/100-1/150; the same for propeller driven aircraft but for jets it's as fast as you can go with the available light. If you want trails left by objects, leave it to 1/50 or so; if you want to freeze action completely, you need to look at 1/8000. 

Bret


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## Gruffs (Dec 10, 2007)

davies20 said:


> Is this not the other way round? Or am i reading it wrong. I thought it was....
> 
> Lots of light - Quick Shutter
> 
> Less light - slow shutter


Yep, this is correct. I'll amend it. I was trying to rush it out before i had to go out.



bretti_kivi said:


> The statement goes like this:
> Bright light --> high shutter speed (1/1000s) with small apertures (f22)
> Dim light --> low shutter speed (1s) with large apertures (f2.8)
> 
> ...


Hi Bret,

I was going to follow on with movt. etc. later on this evening. Shame we can't 'save a draft' really.


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## davies20 (Feb 22, 2009)

Yeah sorry fella i wasnt fault finding. I think you did explain it right just the wording could have been misconstrued.

Good on you for righting these up btw, alot of people will find this really usefull, including myself.


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## Gruffs (Dec 10, 2007)

No problem,

Helps me understand it too.


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## Gruffs (Dec 10, 2007)

*More Added*

Right,

This is meant to be a short series of guides to the basics of DSLR usage and the different parameters that can be adjusted to change and/or manipulate and image. Some of it may well be applicable to Compact cameras too.

So, you've pointed your camera at the thing you want to photograph, What happens and what must you do to get a 'good' image?

All the camera does is projects an image that you have pointed it at onto the sensor. That is all. You can adjust how the camera does this to get different effects.

So we'll start with;

*Shutter*

The Camera has a lens, a mirror and a shutter in front of the Sensor. As you point the camera at the scene, the lens is focussing the light to a distance which is where the sensor sits. This is called the Focal or Image Plane. What the Shutter does is block or allow the light to 'hit' the sensor or specifically timed periods. The mirror deflects the image up and through a prism to the viewfinder (the image you look at). So when you press the button halfway, the Auto Focus (AF) and the Metering do their thing, the mirror flicks up and the shutter opens allowing a timed amount of light from the scene onto the shutter.

So all the shutter does is allow the light from the lens to hit the sensor for a specific amount of time. Usually displayed as a fraction of a second (1/100) for less than a second and decimal (1.5") for more than a second. Easier for the LCD I think.

So, the effect this has on an image;

If you imagine the lens as a hosepipe and the amount of light as a pump and light itself as water. To correctly fill a vessel (Exposure), you must allow the correct amount of water out of the hosepipe for that vessel. So, imagine the shutter as your trigger on your hosepipe.

So If the pump is turned up high (loads of light, well lit scene) then you will need to hold the hose open less time than you would if the pump is low (low light) to correctly fill your vessel (Correct Exposure).

So for Bright lighting conditions, You have a faster shutter speed. For less light, you have a slower shutter speed.

Now, varying shutter speed has an effect on technique too. If you have a low light situation, then you need your shutter open for longer to expose your image. But if you go wobbling the camera around during that exposure, then light meant for a certain pixel, hits a different pixel and you get blur. So you want to have enought light to allow a fast enough shutter speed to expose your image faster than any blur that you induce can mess it up. Or, You stop the wobble (tripod etc).

So if we assume ther is enough light and we ignore the other factors for Exposure for a second..........................

Using the shutter for Motion effects.

Using a fast Shutter speed allows light in from a split second in time. So for things that are moving at a high speed (think if the classic water droplet photo) you have a fast shutter to 'freeze' the action.

You can use this technique also to induce movement into an image. If you have a look at Autosport, there will be a picture with the background blurred and the car nice and sharp. This is done by moving the camera at the same speed as the car to 'freeze' it. But the shutter speed is longer than is required to freeze the background. This is known as panning and is a method of photography using the shutter.

For really long exposure (classic creamy waterfalls). These are on a tripod. The tripod keeps the camera still to prevent any motion blur in things that are not supposed to move. The water is moving and thats what makes it blur selectively.

So, the shutter control specifically controls the time that light from the lens is allowed to expose the sensor.

*ISO*

ISO was an old film term that has been carried over to Sensors to describe their sensativity to the light.

The lower the ISO number, the lower the sensativity of the sensor to light BUT, the quality of the image produced is better. If you boost the sensativity, you lose quality. This loss in quality can be seen as 'noise' or 'hot pixels' or 'grain' although in film some grain was sometimes acceptable. Digital version seems much less desirable. Newer DSLRs are getting much better at higher ISOs though.

So if you find yourself in a Church where no flash can be used to boost your light levels, you can increase the sensativity of your camera to what light there is by increasing the ISO. Remember, a tripod will help to stop blur from your hands trembling allowing a slightly faster shutter speed and less ISO compensation so higher quality images (it's not always possible but you get the idea).

More later..................


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## Gruffs (Dec 10, 2007)

Right,

This is meant to be a short series of guides to the basics of DSLR usage and the different parameters that can be adjusted to change and/or manipulate and image. Some of it may well be applicable to Compact cameras too.

So, you've pointed your camera at the thing you want to photograph, What happens and what must you do to get a 'good' image?

All the camera does is projects an image that you have pointed it at onto the sensor. That is all. You can adjust how the camera does this to get different effects.

So we'll start with;

*Shutter*

The Camera has a lens, a mirror and a shutter in front of the Sensor. As you point the camera at the scene, the lens is focussing the light to a distance which is where the sensor sits. This is called the Focal or Image Plane. What the Shutter does is block or allow the light to 'hit' the sensor or specifically timed periods. The mirror deflects the image up and through a prism to the viewfinder (the image you look at). So when you press the button halfway, the Auto Focus (AF) and the Metering do their thing, the mirror flicks up and the shutter opens allowing a timed amount of light from the scene onto the shutter.

So all the shutter does is allow the light from the lens to hit the sensor for a specific amount of time. Usually displayed as a fraction of a second (1/100) for less than a second and decimal (1.5") for more than a second. Easier for the LCD I think.

So, the effect this has on an image;

If you imagine the lens as a hosepipe and the amount of light as a pump and light itself as water. To correctly fill a vessel (Exposure), you must allow the correct amount of water out of the hosepipe for that vessel. So, imagine the shutter as your trigger on your hosepipe.

So If the pump is turned up high (loads of light, well lit scene) then you will need to hold the hose open less time than you would if the pump is low (low light) to correctly fill your vessel (Correct Exposure).

So for Bright lighting conditions, You have a faster shutter speed. For less light, you have a slower shutter speed.

Now, varying shutter speed has an effect on technique too. If you have a low light situation, then you need your shutter open for longer to expose your image. But if you go wobbling the camera around during that exposure, then light meant for a certain pixel, hits a different pixel and you get blur. So you want to have enought light to allow a fast enough shutter speed to expose your image faster than any blur that you induce can mess it up. Or, You stop the wobble (tripod etc).

So if we assume ther is enough light and we ignore the other factors for Exposure for a second..........................

Using the shutter for Motion effects.

Using a fast Shutter speed allows light in from a split second in time. So for things that are moving at a high speed (think if the classic water droplet photo) you have a fast shutter to 'freeze' the action.

You can use this technique also to induce movement into an image. If you have a look at Autosport, there will be a picture with the background blurred and the car nice and sharp. This is done by moving the camera at the same speed as the car to 'freeze' it. But the shutter speed is longer than is required to freeze the background. This is known as panning and is a method of photography using the shutter.

For really long exposure (classic creamy waterfalls). These are on a tripod. The tripod keeps the camera still to prevent any motion blur in things that are not supposed to move. The water is moving and thats what makes it blur selectively.

So, the shutter control specifically controls the time that light from the lens is allowed to expose the sensor.

*ISO*

ISO was an old film term that has been carried over to Sensors to describe their sensativity to the light.

The lower the ISO number, the lower the sensativity of the sensor to light BUT, the quality of the image produced is better. If you boost the sensativity, you lose quality. This loss in quality can be seen as 'noise' or 'hot pixels' or 'grain' although in film some grain was sometimes acceptable. Digital version seems much less desirable. Newer DSLRs are getting much better at higher ISOs though.

So if you find yourself in a Church where no flash can be used to boost your light levels, you can increase the sensativity of your camera to what light there is by increasing the ISO. Remember, a tripod will help to stop blur from your hands trembling allowing a slightly faster shutter speed and less ISO compensation so higher quality images (it's not always possible but you get the idea).

*Aperture*

Aperture is probably the hardest to get your head around but has the most rewarding of effects if you get it right.

The Aperture is a hole through the lens that is formed by blades. The number and shape of blades varies from lens to lens according to quality and manufacturer. This Aperture can be opened up or closed down to allow more or less light through the lens according to light availability and the effect desired.

How the Apeture works is difficult to describe but basically, the larger the Aperture (Lower f number), the narrow the Depth of field.

Depth of field is the amount of the picture from the camera to infinity distance that is in focus. The larger the depth of field, the wider the band of focus.

As the Aperture narrows, the Depth of field increases. But, as the Aperture is smaller the amount of light is less.

More on this later...........

*Bokeh*

Bokeh is the term used to describe the quality of the Out Of Focus parts of the image. It is subjective to a degree but very definately there. It's something that photographers notice more than non-togs. Maybe that's just because they know what it is. Bokeh is the product of the lens optics and the Aperture shape.

The easiest example to see is if you see candles or Fairy lights that are out of focus, sometimes they are seen as polyagons rather than blurry circles. This is the blades of the aperture not quite making a circle. The higher quality lens have more blades that are better shaped to porduce smooth circles or ellipses.


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## bretti_kivi (Apr 22, 2008)

Sunstars should be in here, too; remember that they also have different numbers of points depending on the number of blades in use.

Bokeh (yes, you can use this if you want):

this picture is pure bokeh, as there's nothing in focus:










I've also just done some demo images with different shutter speeds so you can see what's going on. I'll process and upload those this evening.

Bret


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## davZS (Jul 3, 2009)

Very informative thread I will be a regular :thumb: thanks.


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## bretti_kivi (Apr 22, 2008)

these are the aperture pictures. They go from f3.2 to f16. Focus point has not been changed. Focus distance is around 600mm, so close to the lower limits of the lens, which is a Sigma 24-70/2.8 on a Pentax K5.
No sharpening has been done, they are simply processed to correct potential whitebalance issues (minimal) and ensure consistent exposure. No curves have been applied.

So:

f3.2:









f4:









f5:









f8:









f16:








For the record, the f3.2 pic was 1/6s, and the f16 4s. ISO is 1000 in these.

Bret


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## bretti_kivi (Apr 22, 2008)

A short comment about how these were done:
- they are taken with a Tokina 80-400mm lens on a Pentax K5. Support is a Manfrotto 055 tripod with 222 head connected to the lens tripod support, NOT the camera.
SR was on, the weather was grey and overcast. 
TAv was used, so ISO is selected automatically to compensate for the changing light. ISO goes from 80 to 3200. Aperture used was a consistent f10. Filters used include a .9 ND from Cokin in a P series holder (filter 85mmx85mm) with a 72mm ring.

Now that's out of the way, here the effect that shutter speed has on one specific genre: movement. The road in question has a 50km/h limit (that's 30mph) and it's around 100m down the hill from me. These were taken at 400mm.

1/8s:









1/20s:









1/40s:









1/100s:








1/125s:









1/500s (note the grain as I'm seriously pushing the limits of the possible in crap light: 1/500, f10, ISO3200)









These two are an example of what you can do if you use a filter to artificially limit the light coming in through the lens. In this case, I've limited it by three (f) stops. That's a discussion for later, this is about the effect the shutter speed has on the output.

4s (with filter)









1/2s (with filter)









- Bret


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## Natalie (Jan 19, 2011)

Subscribed, recently got my 1st DSLR so all this is really helpful. Thanks.


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## Gruffs (Dec 10, 2007)

*More Added*

*Really good to get your input Bret. As you have the images, perhaps you could intersect them into the text? Anyone else who wants to contribute, feel free.*

This is meant to be a short series of guides to the basics of DSLR usage and the different parameters that can be adjusted to change and/or manipulate and image. Some of it may well be applicable to Compact cameras too.

So, you've pointed your camera at the thing you want to photograph, What happens and what must you do to get a 'good' image?

All the camera does is projects an image that you have pointed it at onto the sensor. That is all. You can adjust how the camera does this to get different effects.

So we'll start with;

*Shutter*

The Camera has a lens, a mirror and a shutter in front of the Sensor. As you point the camera at the scene, the lens is focussing the light to a distance which is where the sensor sits. This is called the Focal or Image Plane. What the Shutter does is block or allow the light to 'hit' the sensor or specifically timed periods. The mirror deflects the image up and through a prism to the viewfinder (the image you look at). So when you press the button halfway, the Auto Focus (AF) and the Metering do their thing, the mirror flicks up and the shutter opens allowing a timed amount of light from the scene onto the shutter.

So all the shutter does is allow the light from the lens to hit the sensor for a specific amount of time. Usually displayed as a fraction of a second (1/100) for less than a second and decimal (1.5") for more than a second. Easier for the LCD I think.

So, the effect this has on an image;

If you imagine the lens as a hosepipe and the amount of light as a pump and light itself as water. To correctly fill a vessel (Exposure), you must allow the correct amount of water out of the hosepipe for that vessel. So, imagine the shutter as your trigger on your hosepipe.

So If the pump is turned up high (loads of light, well lit scene) then you will need to hold the hose open less time than you would if the pump is low (low light) to correctly fill your vessel (Correct Exposure).

So for Bright lighting conditions, You have a faster shutter speed. For less light, you have a slower shutter speed.

Now, varying shutter speed has an effect on technique too. If you have a low light situation, then you need your shutter open for longer to expose your image. But if you go wobbling the camera around during that exposure, then light meant for a certain pixel, hits a different pixel and you get blur. So you want to have enought light to allow a fast enough shutter speed to expose your image faster than any blur that you induce can mess it up. Or, You stop the wobble (tripod etc).

So if we assume ther is enough light and we ignore the other factors for Exposure for a second..........................

Using the shutter for Motion effects.

Using a fast Shutter speed allows light in from a split second in time. So for things that are moving at a high speed (think if the classic water droplet photo) you have a fast shutter to 'freeze' the action.

You can use this technique also to induce movement into an image. If you have a look at Autosport, there will be a picture with the background blurred and the car nice and sharp. This is done by moving the camera at the same speed as the car to 'freeze' it. But the shutter speed is longer than is required to freeze the background. This is known as panning and is a method of photography using the shutter.

For really long exposure (classic creamy waterfalls). These are on a tripod. The tripod keeps the camera still to prevent any motion blur in things that are not supposed to move. The water is moving and thats what makes it blur selectively.

So, the shutter control specifically controls the time that light from the lens is allowed to expose the sensor.

*ISO*

ISO was an old film term that has been carried over to Sensors to describe their sensativity to the light.

The lower the ISO number, the lower the sensativity of the sensor to light BUT, the quality of the image produced is better. If you boost the sensativity, you lose quality. This loss in quality can be seen as 'noise' or 'hot pixels' or 'grain' although in film some grain was sometimes acceptable. Digital version seems much less desirable. Newer DSLRs are getting much better at higher ISOs though.

So if you find yourself in a Church where no flash can be used to boost your light levels, you can increase the sensativity of your camera to what light there is by increasing the ISO. Remember, a tripod will help to stop blur from your hands trembling allowing a slightly faster shutter speed and less ISO compensation so higher quality images (it's not always possible but you get the idea).

*Aperture*

Aperture is probably the hardest to get your head around but has the most rewarding of effects if you get it right.

The Aperture is a hole through the lens that is formed by blades. The number and shape of blades varies from lens to lens according to quality and manufacturer. This Aperture can be opened up or closed down to allow more or less light through the lens according to light availability and the effect desired.

How the Apeture works is difficult to describe but basically, the larger the Aperture (Lower f number), the narrow the Depth of field.

Depth of field is the amount of the picture from the camera to infinity distance that is in focus. The larger the depth of field, the wider the band of focus.

As the Aperture narrows, the Depth of field increases. But, as the Aperture is smaller the amount of light is less.

More on this later...........

*Bokeh*

Bokeh is the term used to describe the quality of the Out Of Focus parts of the image. It is subjective to a degree but very definately there. It's something that photographers notice more than non-togs. Maybe that's just because they know what it is. Bokeh is the product of the lens optics and the Aperture shape.

The easiest example to see is if you see candles or Fairy lights that are out of focus, sometimes they are seen as polyagons rather than blurry circles. This is the blades of the aperture not quite making a circle. The higher quality lens have more blades that are better shaped to porduce smooth circles or ellipses.

So, you can probably see from the brief explaination that Exposure is a balance between Shutter, Aperture and ISO. There is White Balance and some other things to consider too but we will get to them later on.

*'Stops'*

So, you will hear and read photographers describing something called a 'Stop'. a stop is a unit of measure that describes a doubling or halving in expposure value (EV). So, one 'stop' up or down in exposure can be achieved in Shutter speed, Aperture size or ISO Value as described here;

SHUTTER SPEED;

Its measured in seconds so if the time doubles then you have gone up a stop, if it halves then you've gone down a stop.
eg. Separations of one stop from less light to more light would be..
1/500s 1/250s 1/125s 1/60s 1/30s 1/15s 1/8s 1/4s 1/2s 1s

APERTURE;

Separations of one stop from less light to more light are for example…
f22 f16 f11 f8 f5.6 f4 f2.8

ISO

As ISO doubles, then you go up one stop, as it halves you go down a stop.
eg. Separations of one stop from less light to more light would be..
50 100 200 400 800 1600 3200

Most cameras will allow you to vary exposure by half a stop! So you may see values in between the ones I've shown here! Don't worry the rules are the same.

Camera Modes;

On my Nikon, I have 4 modes.

S, A, M and P.

Other brands call them something different. I'll stick to these to avoid confusion.

**********
_・Mode P (Programmed Auto)

The camera automatically adjusts aperture and shutter speed for optimal exposure, but the photographer can choose from different combinations of aperture and shutter speed that will produce the same exposure. This is known as flexible program.

・Mode S (Shutter-Priority Auto)

The photographer chooses the shutter speed and the camera automatically adjusts aperture for optimal exposure.

・Mode A (Aperture-Priority Auto)

The photographer chooses the aperture and the camera automatically adjusts shutter speed for optimal exposure.

Notethat in all three modes-P, S, and A-exposure is automatically adjusted for optimal results.

・Mode M (Manual)

The photographer chooses both aperture and shutter speed, providing the greatest latitude for creative expression. Choosing the wrong combination could, however, result in photographs that are too bright (overexposed) or too dark (underexposed). We therefore recommend using the camera exposure indicator as a guide when choosing aperture and shutter speed._

_Taken from the Nikon Website_

*************

That last bit is in the manual but i included it for completeness.

There is an excellent pictorial guide to Depth Of Field here

This is a site that allows you to play with the settings and see it's effects on the image. 
Have A Play Here


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## Gruffs (Dec 10, 2007)

*More added*

*Really good to get your input Bret. As you have the images, perhaps you could intersect them into the text? Anyone else who wants to contribute, feel free.*

This is meant to be a short series of guides to the basics of DSLR usage and the different parameters that can be adjusted to change and/or manipulate and image. Some of it may well be applicable to Compact cameras too.

So, you've pointed your camera at the thing you want to photograph, What happens and what must you do to get a 'good' image?

All the camera does is projects an image that you have pointed it at onto the sensor. That is all. You can adjust how the camera does this to get different effects.

So we'll start with;

*Shutter*

The Camera has a lens, a mirror and a shutter in front of the Sensor. As you point the camera at the scene, the lens is focussing the light to a distance which is where the sensor sits. This is called the Focal or Image Plane. What the Shutter does is block or allow the light to 'hit' the sensor or specifically timed periods. The mirror deflects the image up and through a prism to the viewfinder (the image you look at). So when you press the button halfway, the Auto Focus (AF) and the Metering do their thing, the mirror flicks up and the shutter opens allowing a timed amount of light from the scene onto the shutter.

So all the shutter does is allow the light from the lens to hit the sensor for a specific amount of time. Usually displayed as a fraction of a second (1/100) for less than a second and decimal (1.5") for more than a second. Easier for the LCD I think.

So, the effect this has on an image;

If you imagine the lens as a hosepipe and the amount of light as a pump and light itself as water. To correctly fill a vessel (Exposure), you must allow the correct amount of water out of the hosepipe for that vessel. So, imagine the shutter as your trigger on your hosepipe.

So If the pump is turned up high (loads of light, well lit scene) then you will need to hold the hose open less time than you would if the pump is low (low light) to correctly fill your vessel (Correct Exposure).

So for Bright lighting conditions, You have a faster shutter speed. For less light, you have a slower shutter speed.

Now, varying shutter speed has an effect on technique too. If you have a low light situation, then you need your shutter open for longer to expose your image. But if you go wobbling the camera around during that exposure, then light meant for a certain pixel, hits a different pixel and you get blur. So you want to have enought light to allow a fast enough shutter speed to expose your image faster than any blur that you induce can mess it up. Or, You stop the wobble (tripod etc).

So if we assume ther is enough light and we ignore the other factors for Exposure for a second..........................

Using the shutter for Motion effects.

Using a fast Shutter speed allows light in from a split second in time. So for things that are moving at a high speed (think if the classic water droplet photo) you have a fast shutter to 'freeze' the action.

You can use this technique also to induce movement into an image. If you have a look at Autosport, there will be a picture with the background blurred and the car nice and sharp. This is done by moving the camera at the same speed as the car to 'freeze' it. But the shutter speed is longer than is required to freeze the background. This is known as panning and is a method of photography using the shutter.

For really long exposure (classic creamy waterfalls). These are on a tripod. The tripod keeps the camera still to prevent any motion blur in things that are not supposed to move. The water is moving and thats what makes it blur selectively.

So, the shutter control specifically controls the time that light from the lens is allowed to expose the sensor.

*ISO*

ISO was an old film term that has been carried over to Sensors to describe their sensativity to the light.

The lower the ISO number, the lower the sensativity of the sensor to light BUT, the quality of the image produced is better. If you boost the sensativity, you lose quality. This loss in quality can be seen as 'noise' or 'hot pixels' or 'grain' although in film some grain was sometimes acceptable. Digital version seems much less desirable. Newer DSLRs are getting much better at higher ISOs though.

So if you find yourself in a Church where no flash can be used to boost your light levels, you can increase the sensativity of your camera to what light there is by increasing the ISO. Remember, a tripod will help to stop blur from your hands trembling allowing a slightly faster shutter speed and less ISO compensation so higher quality images (it's not always possible but you get the idea).

*Aperture*

Aperture is probably the hardest to get your head around but has the most rewarding of effects if you get it right.

The Aperture is a hole through the lens that is formed by blades. The number and shape of blades varies from lens to lens according to quality and manufacturer. This Aperture can be opened up or closed down to allow more or less light through the lens according to light availability and the effect desired.

How the Apeture works is difficult to describe but basically, the larger the Aperture (Lower f number), the narrow the Depth of field.

Depth of field is the amount of the picture from the camera to infinity distance that is in focus. The larger the depth of field, the wider the band of focus.

As the Aperture narrows, the Depth of field increases. But, as the Aperture is smaller the amount of light is less.

More on this later...........

*Bokeh*

Bokeh is the term used to describe the quality of the Out Of Focus parts of the image. It is subjective to a degree but very definately there. It's something that photographers notice more than non-togs. Maybe that's just because they know what it is. Bokeh is the product of the lens optics and the Aperture shape.

The easiest example to see is if you see candles or Fairy lights that are out of focus, sometimes they are seen as polyagons rather than blurry circles. This is the blades of the aperture not quite making a circle. The higher quality lens have more blades that are better shaped to porduce smooth circles or ellipses.

So, you can probably see from the brief explaination that Exposure is a balance between Shutter, Aperture and ISO. There is White Balance and some other things to consider too but we will get to them later on.

*'Stops'*

So, you will hear and read photographers describing something called a 'Stop'. a stop is a unit of measure that describes a doubling or halving in expposure value (EV). So, one 'stop' up or down in exposure can be achieved in Shutter speed, Aperture size or ISO Value as described here;

SHUTTER SPEED;

Its measured in seconds so if the time doubles then you have gone up a stop, if it halves then you've gone down a stop.
eg. Separations of one stop from less light to more light would be..
1/500s 1/250s 1/125s 1/60s 1/30s 1/15s 1/8s 1/4s 1/2s 1s

APERTURE;

Separations of one stop from less light to more light are for example…
f22 f16 f11 f8 f5.6 f4 f2.8

ISO

As ISO doubles, then you go up one stop, as it halves you go down a stop.
eg. Separations of one stop from less light to more light would be..
50 100 200 400 800 1600 3200

Most cameras will allow you to vary exposure by half a stop! So you may see values in between the ones I've shown here! Don't worry the rules are the same.

Camera Modes;

On my Nikon, I have 4 modes.

S, A, M and P.

Other brands call them something different. I'll stick to these to avoid confusion.

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_・Mode P (Programmed Auto)

The camera automatically adjusts aperture and shutter speed for optimal exposure, but the photographer can choose from different combinations of aperture and shutter speed that will produce the same exposure. This is known as flexible program.

・Mode S (Shutter-Priority Auto)

The photographer chooses the shutter speed and the camera automatically adjusts aperture for optimal exposure.

・Mode A (Aperture-Priority Auto)

The photographer chooses the aperture and the camera automatically adjusts shutter speed for optimal exposure.

Notethat in all three modes-P, S, and A-exposure is automatically adjusted for optimal results.

・Mode M (Manual)

The photographer chooses both aperture and shutter speed, providing the greatest latitude for creative expression. Choosing the wrong combination could, however, result in photographs that are too bright (overexposed) or too dark (underexposed). We therefore recommend using the camera exposure indicator as a guide when choosing aperture and shutter speed._

_Taken from the Nikon Website_

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That last bit is in the manual but i included it for completeness.

There is an excellent pictorial guide to Depth Of Field here

This is a site that allows you to play with the settings and see it's effects on the image. 
Have A Play Here

So, as you can see, getting the balance right is important. If you have action you want to freeze, you need a fast shutter speed. But, if that fast shutter speed then leads to and under-exposed image, you need to open up your aperture. If that Aperture then results in a DOF that is too narrow or undesirable, you need to go to the maximum aperture you can and increase your ISO.

When practicing with your DSLR, try in M mode to take and image that you are happy with. Then switch the camera to auto and look at the settings the camera has chosen. Are they the same? Why are they different. soon enough you'll not need the Auto and be deliberately looking to move away from these settings to achieve a different type of image.

I hope this is of some use to someone.

Gruffs.


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## bretti_kivi (Apr 22, 2008)

I'll integrate some when I get the opportunity, maybe even this evening.

Bret


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