Aperture & Shutter Speed

[ctorry]

I have a question in relation to the Aperture and Shutter priority modes on my camera (Canon 450D).

Can somebody please explain to me why the camera sets a slow shutter speed when using Aperture mode. Correct me if I am incorrect but I feel that setting a slow shutter speed with a aperture of say f5.6 overexposes the photo.

Vise Versa with the Shutter Priorty mode if I set what I feel is the correct shutter speed (based on below formula in the example - could also be wrong). The shutter sets an aperture of say f16, which I feel underexposes the photo.

Example

From my readings, if say I am using a 70 mm lens and hand holding the camera that my shutter speed should be at least 1/150 to avoid motion blur. I think 1/150 is 6 stops.

This would then allow me to move up 6 Stops in Apeture F8.

Would I be better off changing to setting the shutter speed and aperture manually until I buy a Tripod.

Please forgive me if this question does not make sense or if it has been posted previoulsy.

Your assistance is greatly appreciated.

Craig.

[Scotty72]

Remember, if you are not happy with the shutter speed the camera gives you, you can dial in some negative exposure compensation to give less exposure (and this will raise the shutter speed) or you can up the ISO.

Scotty

[rwg717]

There is a very informative section over in the "new to photography" forum which will help you heaps! A six stops up in Ap or Tv don't necessarily mean a contr-adjustment in reverse! There is a fair bit more than that going on, after all it's all about the light, if there isn't enough you need to add some, if that's not possible then increase the ISO setting.

High ISO (eg.1600) presents its own problems too but adding light is the answer...think you would benefit from the tutorials in AP:D
Richard

[rwg717]

This is the section I wanted to post:-

http://www.ausphotography.net.au/forum/showthread.php?t=24087

Very instructive:)
Richard

[ctorry]

Thanks for getting back to me guys.

Greatly appreciated.

[OzzieTraveller]

G'day Craig

Reading your Q leads me to wonder just a bit more ...
Bear in mind that the camera must set a speed & aperture combination to give you correct exposure at all times. You are asking about speeds (after setting the aperture) and apertures (after setting the speeds)

When you are in Aperture priority mode what aperture has been selected by you? and
When you are in Shutter mode, what shutter speed has been selected by you?

Each of these answers will dramatically affect the 'other' settings used by the meter to correctly balance the exposure
Maybe the sketch below will help ...

http://i28.tinypic.com/2pt192e.jpg

eg- if the camera (on auto or Program) wants to select f11 x 1/125 sec and you then go to Shutter mode where the speed has been set to 1/30 second, the aperture will be set to f22 simply to balance the exposure (and v/v for setting an aperture and letting the camera find a s/speed)

Does this help at all??
Regards, Phil

[arthurking83]

....

Can somebody please explain to me why the camera sets a slow shutter speed when using Aperture mode.

LIGHT!(or more accurately, lack of it)


.... Correct me if I am incorrect but I feel that setting a slow shutter speed with a aperture of say f5.6 overexposes the photo.



Light is the single most important element in photography.
you don't even need a 'proper' camera to capture images that could be regarded as 'photographs' ... as evidenced by someone recently making 1 year long exposure taken with a pinhole camera recently.

but what you do need is light.

A one year long exposure captured in a totally black cave completely removed forom any light source will result in a black exposure. .. ie. not much light will make a dark image.

First and foremost, learn to understand what your camera's meter is telling you to do.
And then read up and experiment on how the different modes work. Modes such as spot metering, evaluative or centre weighted.. and how they make a difference to what your camera's meter wants to expose.

The other aspect that's important to understand before you start playing with under and over exposure compensation, is how much dynamic range is in the scene you want to capture.

[ctorry]

Thanks for your posts.

Ozzie Traveller you are correct and I think I understand the inverse relationship between aperture and speed (i.e. f11 and 1/125 lets in the same amount of light as f5.6 and 1/500 - great easy to undertstand diagram you have posted also).

arthurking83 I think you have hit the nail on the head what I wasn't taking into account in this equation was the surroundinng light.

I would have thought thought that If I am indoors and in a fair light room and have set the white balance correctly and am photographing with an aperture of f5.6 that the camera would set a shutter speed of faster than 1/20. A slow shutter speed of 1/20 makes it almost impossible to avoid motion blur when hand holding the camera (if my understanding is correct this would be mean that the aperture would be wide open letting in substantial light and also the slow shutter speed would let in substantial light). Maybe I just need to invest in a tripod to avoid the motion blur.

Thanks everybody for their much valued feedback.

ctorry.

[maccaroneski]

Or bump up your ISO....

[Beee]

Ozzie Traveller - I really like that diagram. It makes it so clear to see how the two work together.

ctorry - at least if you are using digital you can experiment away without it costing you a thing! Set your camera on Manual, set your aperture to one setting (f5.6 or whatever you had it in Aperture control) and then change shutter speed by increments for each frame in the same light. Or vice versa. The best way to learn!

[arthurking83]

.....

I would have thought thought that If I am indoors and in a fair light room and have set the white balance correctly and am photographing with an aperture of f5.6 that the camera would set a shutter speed of faster than 1/20. .....

This is why it's important to understand the meaning of the term EV (Exposure Value).

Each scenario will have varying degrees of light, which is what EV refers too.

My small(2.5m x2m) basically all white/grey study will produce similar results when I use matrix metering(ie. getting a reading of the entire room with a wide angle), but if I switch to spot metering and that spot is directed at the black PC case, the metering will tell me that I now need 1/6s shutter speed. But I'm smarter than the camera's metering system, but only because I know that I want the black PC to look black and not grey(as the meter wants it too), so I'll dial in a lot of -ve exposure compensation if I use spot metering to ensure that the black PC turns out black.
The room walls are close to white(but not exactly) so if I spot meter on them, I'll use between +1 to +2 EV in the camera. If I spot meter on the large grey work desk, I'll meter with no compensation or I may dial in -0.3 to -0.7Ev in the camera.. depending on how much colour I want everywhere else.

If you want faster shutter speeds AUTOMATICALLY done by the camera, see maccaroneski's reply above!(use AUTO ISO in the camera).

I generally never use matrix(or in Canon speak.. evaluative) metering as I'm not confident I understand 100% OR exactly what it's trying to do.
I do use Matrix metering when I use flash tho.. it's close to brilliant in Nikon circles :th3:

[OzzieTraveller]

G'day again Craig

I've been thinking a bit more about your Q and possible solutions &/or answers
One possibility just off the top of my head

When a camera is set to Auto, it is unlikely that you will be shown any exposure info as the camera designer assumes "auto user == you're not interested"

However, if you set the camera to Program, you will be shown the camera's choices of speed & aperture that it will use when you press the button.
This starts to become useful as you will then see some sort of a pattern in speeds & apertures as you swing the camera around a scene, the light level goes up & down and so do the camera's choice of exposure settings.

Some cameras have a "command dial" near the shutter release, [it gets different names from different camera makers] ... others use the Up/Down keys in the "OKay" block ... find out what your camera does
The beauty of running in Program mode is that (with most cameras) you can rotate the command dial at any time to alter the settings for the next exposure - after that it goes back to Program again
Rotate left (say) and the s/speed goes up, rotate right (say) and the s/speed goes down ... the beauty of this is that [I]you will see the light meter altering the 'other' settings to always keep the exposure in balance ... and hopefully from this, you will get a better idea of how to run the camera [in the future] in either Aperture mode or Shutter mode, depending upon your subject matter

Hope this helps a bit
Regards, Phil

[ctorry]

Ozzie Traveller - Thanks for getting back to me on this, I really appreciated your assistance.

The component I was forgetting in my question, which is the most important the amount of light entering the room.

Thanks again.

I went and invested in a tripod last weekend - much better.

ctorry.