TV and AV explination?

[rossw82]

Hey guys,

 

I have just recently found the web site and im really enjoying everything so

far. I haven?t had much experience in photography (other then 1/2 a year at

school about 11yrs ago) and im really enjoying my recent punches of a EOS 300.

 

My question is about TV and AV values.

TV ranges from 2000 to 30" and AV 22 to 4.0.

I am kinda getting used to the AV (although I thought I would have less

background detail in my photo of the dog in my gallery). Can someone give me a

guide to approximate exposure times for tv? i.e. 30"= 30min? And would 22 in AV

give more and 4 less unfocused detail? And does +/- AV change this even more?

 

As I said, this is all still pretty new for me!

 

Thanks in advance for all your help

 

Ross<div></div>

[ken munn]

Av fixes the aperture you shoot at and the camera chooses the best shutter speed.

 

Tv fixes the shutter speed you shoot at and the camera chooses the aperture.

 

Aperture is the size of the variable hole in the middle of the lens. The wider the aperture

(paradoxically, the wider the aperture, the smaller the aperture number) the less

foreground and background around your focus point will be in focus. So for Fido without

too much background detail, shoot with your lens wide open - a number like 2.8, 3.5 or

5.6 depending on which lens you have.

 

Shutter speed has no affect on 'depth of focus' but it does dictate how blurred the image

may be in other ways. Too slow a shutter speed (represented by a number either with a

0" in front of it, or going up to about 60, and unless you're shooting with a solid support

like a tripod or table top, there's a risk that camera movement will blur the photograph,

just because you cannot hold the camera still enough. Also, if Rover is moving, you need a

faster shutter speed to 'freeze' his movement and make him look sharply focussed (see his

tail). The rule of thumb for a shot without photographer-induced blur is at least 1/xth,

where x is the focal length in mm of the lens you're using. So a minimum speed of

1/100th of a second, with a 100mm lens, 1/200 with a 200mm lens, etc.

 

My recommendation. If you're shooting Prince rushing about, set Tv at 250th. If on the

other hand he is sitting still and looking beautiful, set Av at 5.6.

 

Here endeth the first lesson - someone else can explain why ISO matters, and why you'll

get more background blur with a telephoto lens than with a wide angle one.

[zigzag]

You need to do a bit of reading about aperture, shutter speed and ISO. There is both a little and a lot to know. Read about 'Understanding Camera Lenses' at <a href="http://www.cambridgeincolour.com/tutorials.htm">Cambridge In Colour</a>. read about 'Understanding Depth of Field' at <a href="http://www.luminous-landscape.com/tutorials/">Luminous Landscape</a>. Read about technique and getting good photos at <a href="http://philipdunn.blogspot.com/">Philip Dunn's Blog.</a>

[zigzag]

Just a little more: Your Tv (fixed shutter speed) values go from 1/2000s to 30 seconds, the Av (fixed aperture) values (for that lens) go from f/22 to f/4. f/4 is the widest aperture which will give you the shortest depth of field. Depth of field is the near/far distance around a plane of focus within which a subject appears to be in focus (from where you are viewing it.)

 

Simplistically, depth of field is determined by three things: aperture, distance to subject and (perceptually at least) focal length of your lens. As you pick smaller 'f' numbers the depth of field becomes shorter. As you get closer to a subject (at the same setting) the depth of field becomes shorter and as you use a longer lens the apparent depth of field becomes shorter.

 

If you have your dog in focus and the background behind him is close to him then it is possible that the background will be in focus too - so for an out of focus background and an in focus dog you need to get separation between your dog and the background.

 

The thing about digital is that it costs nothing to try stuff. Get an empty card, set the camera to Av mode and try every setting from f/22 to f/4. Shoot somethiing like a fence, trees or line of objects that move away into the distance. Take note of how the shutter speed changes, record the settings and then examine the photos and see how the depth of field changes. Use the calculators to see what you should expect.

 

Try a similar thing with Tv - you need good light to get 1/2000s and night to get 30 seconds but see how aperture changes.

 

Read the links and try things.

[kari v]

Read your camera manual (search one online if you don't have it), borrow some basic books from the library and search the net. You really have some reading to do.

 

Some tips.

 

Aperture: You shouldn't shoot smaller than f11 (f16, 22...) unless you really know you must, image quality will degrade due to diffraction.

For 35mm (and APS-C) f11 provides enough DoF for most situations and often there's not even enough light to shoot at smaller apertures handheld.

 

Handholding: Basic rule is to shoot *at least* at 1/focal lenght to avoid camera shake, eg. 50mm 1/60s, 85mm 1/90s... People are different, of course, but this is a good starting point.

 

Did you scan that dog picture yourself or was is done by a lab? Seems awfully grainy for that size and there's a color cast.

[akajohndoe]

It is all about the intersection of the curves traced by the possible values of the aperture and shutter.

 

There are a number of pairs of values that will yeild "correct" exposure. These sets of Aperture/Shutter pairs are called "Exposure Values" or EV for short.

 

Depending on what your intention is (e.g.: stop action, blur action, shallow depth of field (DOF), Deep DOF) dictates what values you choose.

 

There is a bit more explanation on various websites, including my own, <a href="http://www.akajohndoe.com">AKAJohnDoe.com</a>. Once you understand the relationship between these and learn how to apply Exposure Compensation based on the 18% gray reflectance of in-camera metering systems, you will be well on your way!

[winn]

Try this lik:

 

http://www.shutterfreaks.com/Tips/Exposure/exposure111.pdf

[William Michael]

I explain the the relationship bewtween the three exposure parameters in this post. It might be helpful to understand how the three are related:

 

 

http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=00Leff

 

(Jun 29, 2007; 01:06 a.m.)

 

WW

[mendel_leisk]

As others have said, the explanation of TV and AV values is explained in detail at the back of the manual. One thing that might help is to try to get away from Canon's (and others?) dorky acronyms:

 

TV = Shutter speed

 

AV = Aperture

 

One grumble I have is with Canon's display of shutter speeds between 1/4 second and 1 second. I don't think I'll ever get comfortable with them being displayed in 1/10 of a second intervals. Would much prefer it to go:

 

1/4 second

 

1/2 second

 

1 second

 

And never mind dividing it any finer.

[chchance]

Canon has an excellent explanation of the type the things your asking.

http://web.canon.jp/imaging/enjoydslr/part1/1B.html

[rossw82]

Thanks guys... Its all good stuff. And yes, i have a lot of reading to do!

 

With my photos, they were all done at the lab. I'll get my next film developed somewhere differnet to see if they give me better quality pics.