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Canon uses "Av" (aperture variable) for the automatic exposure mode that entails the user choosing the aperture and the camera body choosing the shutter speed. This mode is called "A" by Nikon, and I think other manufacturers (Panasonic comes to mind, see this review of the GF1).

The mode generally called "S" (shutter priority) is called "Tv" (time variable) by Canon.

Do any other manufacturers use the same designations as Canon?

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1  
Audio/Video Television :P –  Nick Bedford Jan 22 '11 at 22:04
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FTR I'm pretty sure it's "aperture value" and "time value", not "variable", because in these modes, that's the factor that's fixed, not variable. –  mattdm Feb 21 '11 at 3:48
    
@mattdm, it depends on the context. If you talk about 1/200 Tv then it is Time value. But, if you are referring to the dial setting, Tv means vary the Time (shutter speed), while keeping the Aperture constant. So to think of Tv as meaning Time variable is a useful memnonic to mean vary the Time. So when, for example, I set the dial to Av, I know immediately that the Aperture is the variable quantity. This, at least is true on my camera, a Pentax K7 –  labnut Feb 21 '11 at 19:28
    
Really? On my K-7, in Av, the aperture stays constant at what I set it to and the shutter speed varies. And in Tv, the shutter speed stays the same and the aperture changes freely depending on the metering. –  mattdm Feb 21 '11 at 19:42
    
@mattdm, I hate to argue with someone who owns such a fine camera :) But it seems to me we are saying the same thing but attaching different meaning to words. When I say 'Tv means vary the Time)', I mean that I, the photographer, am varying, or controlling the time. You use the word 'set' the time while I use the word 'vary' the time. We both mean that the time is actively controlled by the photographer but use different verbs to describe the action. We both agree that the camera chooses a resultant Aperture. Which is variable? I have defined variable to be the quantity I actively control. –  labnut Feb 21 '11 at 20:10

4 Answers 4

up vote 13 down vote accepted

A quick review of photos of control dials shows the following:

Tv, Av, P, M
Pentax, Canon

S, A, P, M
Nikon, Sony, Olympus, Panasonic, Ricoh, Samsung, Fuji, Sigma

Leica has its own nomenclature.
I had always thought of Tv and Av meaning Time variable and Aperture variable.

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Tv does indeed mean "Time Variable", as Av does indeed mean "Aperture variable". –  jrista Jan 23 '11 at 7:37
    
Thanks, edited the question! –  gerikson Jan 23 '11 at 12:23
    
Interestingly, I'd rather consider the exposure time variable when shooting in Av since I select an aperture and the camera varies the exposure time. Of course, both are variables, but somehow it feels odd that it's more variable when I'm the one who varies them ;-) –  Joey Jan 23 '11 at 12:50
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@jrista: why do you say that it means "... variable"? I just looked in the manual for the Canon 7D, and it says "<Av> stands for Aperture value"..... –  mattdm Feb 21 '11 at 3:52
    
My Canon manual used the term "variable", and many of the books I've read use the same term (others are based on Nikon gear, which seems to use A and S for the same things.) It makes logical sense, given that when set to that mode, you have the control to "vary" a setting. If you are using Av, the Aperture is a variable setting controlled by a dial, and the same goes for Tv. –  jrista Feb 21 '11 at 5:08

It seems that Pentax in general uses the same terms.

pentax k-x review

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+1 They have a couple of others - Sv (Sensitivity) and TAv (Shutter/Apperture) on the semi-pro line. –  John Cavan Jan 22 '11 at 21:00
    
Sv sounds like P mode on a Canon. TAv would be like manual mode, assuming ISO is always independently controlled like on a Canon. –  jrista Jan 23 '11 at 7:39
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@jrista - Sv just allows ISO adjustment using the dials, Pentax also has a program mode, but I'm not sure of the similarity to Canon there as most reviewers seem to think Pentax's implementation is unique. The TAv mode is essentially the same as Canon's manual mode with auto ISO (though, not entirely), in Pentax manual mode is totally manual. They are convenient to have on the mode dial, it's a faster access to some settings without going to the menu. –  John Cavan Jan 23 '11 at 14:37

My first SLR was a Pentax MZ-50 (film camera). It used Av and Tv on the control dial.

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Ooh! Through the power of random Wikipedia link following, I came across an answer to this question. There was a never-caught-on system for calculating exposure called the APEX system, which uses "Ev = Av + Tv = Bv + Sv" — where Av is aperture value and Tv is time value.

However, the scale used by Canon and etc. now is not the base-2 log scale required by APEX. So, while it's likely this is where the term came from, I think it's actually {{citation needed}} if one is going to get really picky.

The Wikipedia article refers to this article by Doug Kerr, which provides some interesting reading.

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