General Photography Rules... (Some help please)

[Amnesia180]

Hi All...

I'm new to photography and would like some confirmation on the few things that I've already learnt in my journey.

Aperture -
A large f/-value such as f/2.8 will give a larger opening, allowing more light in, which will also give a shallower DOF.
A smaller f/-value such as f/11.0 will give a smaller opening, allowing less light in, giving a larger DOF.

Shutter Speed -
Determines the length of time light comes through the aperture.
The slower the shutter speed (the smaller the number), the longer the shutter remains open (such as 1/2).
The faster the shutter speed (the larger the number), the less time the shutter remains open (such as 1/250).

Exposure Indicator -
I can manually adjust this to over/under exposue the photo (to get a brighter/darker photo).

Now... here is me putting the theory above into practice.

A couple of scenarios:
Scenario 1 - Moving stream.
I would mount my camera onto a tripod. Choose a small aperture to keep the a larger DOF. Have a slower shutter speed to give the effect the running stream is actually running.
Here's what I would roughly chose (in natural daylight... good conditions, not overcast etc).
ISO - 200. F/11. 1/4. Am I right in saying this should have a large DOF (keeping lots of the image sharp and in focus) and the running stream will have "motion blur" looking like it's still moving in the final photo?

Scenario 2 - Still bird.
I would chose a larger aperture so the only thing in focus would be the moving bird. By having a larger aperture I would be able to chose a faster shutter speed (because more light is allowed in) meaning I should be able to capture the bird in flight.
Here are the settings (again, assuming natural daylight etc).
ISO - 200. F/2.8. 1/1000. Am I right in saying this should capture the bird in flight, keeping the majority of the subject in focus.



Now, all of what I have said is only in theory, based on my understand on Exposure/Aperture/Shutter Speed.

Here is where it gets difficult - How does changing the focal length affect the DOF? This is where I seem to get confused.

If you check my other post, you can see the errors I am getting in my photos.

Sorry for the long post.

Thanks,
Amnesia

 

[Gary Bagshawe]

Yep the theory is there but in practice..... getting 1/4 sec at f11 at iso 200 on a bright clear day is really gonna give you problems. The best thing to do is go out and practice your theories yourself. Then post a couple of pics explaining what you were after and if you didn't get it quite right ask people what went wrong.

 

[CT]

Hi All...

I'm new to photography and would like some confirmation on the few things that I've already learnt in my journey.

Aperture -
A large f/-value such as f/2.8 will give a larger opening, allowing more light in, which will also give a shallower DOF.
A smaller f/-value such as f/11.0 will give a smaller opening, allowing less light in, giving a larger DOF.

Shutter Speed -
Determines the length of time light comes through the aperture.
The slower the shutter speed (the smaller the number), the longer the shutter remains open (such as 1/2).
The faster the shutter speed (the larger the number), the less time the shutter remains open (such as 1/250).

Exposure Indicator -
I can manually adjust this to over/under exposue the photo (to get a brighter/darker photo).

Now... here is me putting the theory above into practice.

A couple of scenarios:
Scenario 1 - Moving stream.
I would mount my camera onto a tripod. Choose a small aperture to keep the a larger DOF. Have a slower shutter speed to give the effect the running stream is actually running.
Here's what I would roughly chose (in natural daylight... good conditions, not overcast etc).
ISO - 200. F/11. 1/4. Am I right in saying this should have a large DOF (keeping lots of the image sharp and in focus) and the running stream will have "motion blur" looking like it's still moving in the final photo?

Scenario 2 - Still bird.
I would chose a larger aperture so the only thing in focus would be the moving bird. By having a larger aperture I would be able to chose a faster shutter speed (because more light is allowed in) meaning I should be able to capture the bird in flight.
Here are the settings (again, assuming natural daylight etc).
ISO - 200. F/2.8. 1/1000. Am I right in saying this should capture the bird in flight, keeping the majority of the subject in focus.



Now, all of what I have said is only in theory, based on my understand on Exposure/Aperture/Shutter Speed.

Well done you're pretty well right on the money with all of that.

Here is where it gets difficult - How does changing the focal length affect the DOF? This is where I seem to get confused.

That's pretty straightforward really - the longer the focal length of a lens, the less depth of field it will have to start with. Regardless of the focal length though, any lens will have the least DOF when its focused at very close distances (macro is the extreme example of this problem when DOF is just a couple of millimetres or even less) but the DOF gradually increases as you focus further away from the camera.

Extreme wide angle lenses on the other hand (having such a short focal length} have such huge inherent DOF that often you hardly need to focus much at all.

That's the bones of it.

 

[Amnesia180]

Thanks for the explanations.

I'm going to take some photos tonight of maybe running water or something... see what results I can get.

Now, if for instance I couldn't get the shutter speed to react quick enough - by upping the ISO to say 800, that's gone up 2 stops, so I would need to reduce the aperture two stops to allow for a quicker shutter speed? Is that how it works?

 

[Gary Bagshawe]

Pretty much, but the higher the iso the more noise (grain for us oldies) is introduced to the image. This can be used for effect at times to give a more moody gritty image.

 

[rpstewart]

Now, if for instance I couldn't get the shutter speed to react quick enough - by upping the ISO to say 800, that's gone up 2 stops, so I would need to reduce the aperture two stops to allow for a quicker shutter speed? Is that how it works?

Not quite. ISO, aperture and shutter speed work together to form the exposure, for any given scene there is a correct "exposure value" or eV, you need to then set (or allow the camera to set) the three parameters correctly to match the eV required. If for any reason you need to change one of those parameters (a faster shutter speed to freeze action for example) then you need to compensate for that change by altering one or occasionally both of the other two.

In the example you give above if you want to increase the shutter speed then upping the ISO is correct however you don't need to change the aperture as well. Doing that would negate the effect of the ISO change and not allow you to change the shutter speed while keeping the exposure correct.

 

[Amnesia180]

Not quite. ISO, aperture and shutter speed work together to form the exposure, for any given scene there is a correct "exposure value" or eV, you need to then set (or allow the camera to set) the three parameters correctly to match the eV required. If for any reason you need to change one of those parameters (a faster shutter speed to freeze action for example) then you need to compensate for that change by altering one or occasionally both of the other two.

In the example you give above if you want to increase the shutter speed then upping the ISO is correct however you don't need to change the aperture as well. Doing that would negate the effect of the ISO change and not allow you to change the shutter speed while keeping the exposure correct.

It all makes sense now

So by upping the ISO to 800, I've already compensated because what I wanted to do was increase the speed of the shutter?

I understand! Now for the hard part... putting it into practice this evening. I hope the sun still shines for an hour or so after 6pm when I finish.

 

[ShawWellPete]

This is a nice thing to play with.