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JetJock22
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Posts: 612
Joined: Thu Jun 03, 2004 12:13 pm

Basic Photography Help

Mon Feb 05, 2007 11:05 am

There is one thing that I just get plain confused about when it comes to taking photos. Can someone kindly explain the difference between AV mode and TV mode for canon digital cameras in simple terms? I am really trying my best to learn and think if I have that extra little push so to speak, I might just get the hang of it. Thank you for any help you can give.
 
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dvincent
Posts: 1592
Joined: Mon Jan 01, 2007 9:53 am

RE: Basic Photography Help

Mon Feb 05, 2007 11:32 am

Av Mode = Aperture priority. You set the lens aperture, and the camera calculates the proper shutter speed.

Tv Mode = Shutter Priority. You set the shutter speed, and the camera picks the appropriate aperture.

It works just like Auto/Program exposure except you can influence one of the variables. You're not on the hook for the whole exposure - you're just helping to direct what kind of shot you want.

Generally, you use Av mode when you value a specific depth of field, and Tv mode when you want to freeze action or show motion blur. Want to freeze a baseball player hitting the ball? Use Tv and 1/1000s. How about a portrait? Use Av and f/2.8. Those are just a few examples.

Canon has a very good online guide explaining these features of their cameras, I'm sure you'd like to read it.

http://www.photoworkshop.com/canon/index.html
From the Mind of Minolta
 
ClueLessInFra
Posts: 32
Joined: Fri Nov 25, 2005 6:58 pm

RE: Basic Photography Help

Mon Feb 05, 2007 11:41 am

In Tv you have to select an exposure time, the camera will choose a proper aperture.
In Av you have to select an aperture, the camera will choose a proper exposure time.

Exposure time depends on focal length. A simple rule is to use
Exposure time = 1 / focal length
or (if Rebel or 20D/30D is used)
1 / (focal length * 1,6)
IS comes handy for low light situations for it will allow you to use longer exposure times. IS doesn't help (well, most of the time) fixing fast moving object.

Aperture depends ... well ... it's more complicated. Simply spocken: The smaller the aperture number is, the smaller your Depth of Field (DOF) will be for a given distance. A simple DOF-calculator will be found at www.dofmaster.com

Ciao, Walter
 
JetJock22
Topic Author
Posts: 612
Joined: Thu Jun 03, 2004 12:13 pm

RE: Basic Photography Help

Mon Feb 05, 2007 11:47 am

Thanks for the help guys. I will definately check out the links. For aircraft shooting in lets say in normal sunny conditions, would I use av or tv mode? I have a 75-300mm lens if that helps...thanks again for your patience.
 
ClueLessInFra
Posts: 32
Joined: Fri Nov 25, 2005 6:58 pm

RE: Basic Photography Help

Mon Feb 05, 2007 12:09 pm

Both is possible and both has pros and cons.
Take your time to find out which one suits you better.
I would suggest to start with static planes from near and from far using Tv mode and 1/500 s shutter speed (for 300 mm). See formula above for calculations. Your mileage may vary. You will soon find out how DOF and aperture are working together and - based on a better knowledge why and how a camera is working - will be able to judge on that base.
Don't worry!

Ciao, Walter
 
JetJock22
Topic Author
Posts: 612
Joined: Thu Jun 03, 2004 12:13 pm

RE: Basic Photography Help

Mon Feb 05, 2007 12:22 pm

Ok, 1 more question and I promise that is all for now - when in av mode, the numbers that scroll up and down, ex. 8.0 up to 11.0, etc, those are the f stops correct? And if I am correct, what does that control? Thanks again.
 
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dvincent
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Joined: Mon Jan 01, 2007 9:53 am

RE: Basic Photography Help

Mon Feb 05, 2007 12:55 pm

Quoting JetJock22 (Reply 5):
Ok, 1 more question and I promise that is all for now - when in av mode, the numbers that scroll up and down, ex. 8.0 up to 11.0, etc, those are the f stops correct? And if I am correct, what does that control? Thanks again.

You guess correctly; those are the f/stops. It controls the opening of the iris in the lens. A larger number (f/8) is a small opening, which lets in less light while a small number (2.8) is a large opening that lets in more light. When you use a smaller aperture, you let in less overall light, requiring longer exposure times for a similar exposure.

EG, if you meter 1/500s time at f/4, you would need 1/125s at f/8 for an "equal" amount of light to hit the sensor. The difference will be that the background will be blurrier at f/4 as opposed to f/8. The narrower the aperture, the larger depth of field you will get, which means the larger the area of focus.

For a heads-and-shoulders portrait, you'd want to use f/2.8 (or sometimes even less) to keep just the head and shoulders in focus, while blurring out the background. In a situation where you want to have a lot in focus, like a landscape (or an airplane landing on a runway), a smaller f/number like f/8 is more useful to keep more in focus.

By controlling what is in and out of focus, you emphasize the subject over unimportant details. The best way to get a feel for this is to go out and play with your camera; take pictures of the same subject at different f/stops (a flower is great for this) and you'll see the difference. Digital makes experimenting painless and fun, so give it a go and you'll get the hang of it quickly.
From the Mind of Minolta
 
CalgaryBill
Posts: 618
Joined: Thu May 04, 2006 12:27 am

RE: Basic Photography Help

Mon Feb 05, 2007 3:24 pm

Picking away at "learning photography" one question at a time is going to leave a lot of big holes in your knowledge (not to mention the mis-information you'll get from well-meaning photographers that learned the same way you're trying).

Go out and buy the book "The Camera" by Ansel Adams, it will give you a solid foundation of what's going on in that little, black box. When you're done with that one, read "The Negative" also by Adams, it'll teach you a heck of a lot about exposure (it might be about film, but most of the same rules apply to digital).

B

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