From: the_niner_nation on
As per title, what is the difference between these 2 shooting modes?
According to the manual, both allow you to define or set your own aperture
whilst the camera sets a shuuter speed to deliver a correct exposure...if
thats the case, then why are there 2 modes ro do almost the same thing?

Thanks!!



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From: Alan Browne on
the_niner_nation wrote:
> As per title, what is the difference between these 2 shooting modes?
> According to the manual, both allow you to define or set your own aperture
> whilst the camera sets a shuuter speed to deliver a correct exposure...if
> thats the case, then why are there 2 modes ro do almost the same thing?

"P" mode makes an initial selection for you of both aperture and speed
(based on metered light, ISO setting, max lens aperture and Canon's
particular P algorithm) and then lets you "program shift" as desired in
either aperture or speed.

"Av" locks the exposure speed according to your chosen aperture (and ISO
setting). You vary the aperture only.

On top of both of the above is the exposure-compensation that you enter
to offset for the metering.

Cheers,
Alan.

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From: HEMI-Powered on
the_niner_nation offered these thoughts for the group's
consideration of the matter at hand:

> As per title, what is the difference between these 2 shooting
> modes? According to the manual, both allow you to define or
> set your own aperture whilst the camera sets a shuuter speed
> to deliver a correct exposure...if thats the case, then why
> are there 2 modes ro do almost the same thing?
>
P generally meaning "programmed auto", attempts to reach a best
compromise between shutter speed and aperture so that you don't
get camera shake from a too low shutter speed nor too shallow DOF
due to a too wide aperture. But, it is a compromise.

Av means "aperture priority" which assumes you know that you know
the correct aperture for the effect you want, e.g., really broad
or really shallow DOF, and it adjusts shutter speed to create a
correct exposure.

Tv means "shutter priority", which assumes you know what effect
you want from shutter speed, e.g., some blur to show motion or
absolute stop-action, and it adjusts aperture accordingly.

To use Av and Tv effectively, you have to keep a close eye on the
shutter and aperture shown in the viewfinder to ensure that it
will be "correct" for what you want to achieve. It REALLY helps
if you have a good founding in the principles of photography so
that you can reasonably estimate the shutter speed or aperture to
any given effect you want to achieve. Could they be combined?
Yes, but it is simpler to think in terms of what you want to
control and let the camera do the math on the other setting. A
true combination does exist - P.

I find with my Rebel XT that when I try to out-think the camera
with Av, I usually blow it, so about the only time I use it is
when I have a specific DOF effect I want to achieve. I don't
shoot things that move, so I've never tried Tv. All things
considered, I think the Rebel does a damn fine job of balancing
shutter and aperture on P.

--
HP, aka Jerry
From: HEMI-Powered on
Alan Browne offered these thoughts for the group's consideration
of the matter at hand:

> the_niner_nation wrote:
>> As per title, what is the difference between these 2 shooting
>> modes? According to the manual, both allow you to define or
>> set your own aperture whilst the camera sets a shuuter speed
>> to deliver a correct exposure...if thats the case, then why
>> are there 2 modes ro do almost the same thing?
>
> "P" mode makes an initial selection for you of both aperture
> and speed (based on metered light, ISO setting, max lens
> aperture and Canon's particular P algorithm) and then lets you
> "program shift" as desired in either aperture or speed.
>
> "Av" locks the exposure speed according to your chosen
> aperture (and ISO setting). You vary the aperture only.
>
> On top of both of the above is the exposure-compensation that
> you enter to offset for the metering.
>
I added Tv because it is a natural adjunct to the OP's overall
question. You correctly amplified my remarks by noting that ISO
modifies how all 3 modes will compute, and the camera's AE can be
overridden to at least +/- 2 stops. I don't do that much, but isn't
that EV?

--
HP, aka Jerry
From: Alan Browne on
HEMI-Powered wrote:
> Alan Browne offered these thoughts for the group's consideration
> of the matter at hand:
>
>
>>the_niner_nation wrote:
>>
>>>As per title, what is the difference between these 2 shooting
>>>modes? According to the manual, both allow you to define or
>>>set your own aperture whilst the camera sets a shuuter speed
>>>to deliver a correct exposure...if thats the case, then why
>>>are there 2 modes ro do almost the same thing?
>>
>>"P" mode makes an initial selection for you of both aperture
>>and speed (based on metered light, ISO setting, max lens
>>aperture and Canon's particular P algorithm) and then lets you
>>"program shift" as desired in either aperture or speed.
>>
>>"Av" locks the exposure speed according to your chosen
>>aperture (and ISO setting). You vary the aperture only.
>>
>>On top of both of the above is the exposure-compensation that
>>you enter to offset for the metering.
>>
>
> I added Tv because it is a natural adjunct to the OP's overall
> question. You correctly amplified my remarks by noting that ISO

eh? I answered first, so you're the one amplifying... ;-)

> modifies how all 3 modes will compute, and the camera's AE can be
> overridden to at least +/- 2 stops. I don't do that much, but isn't
> that EV?

I didn't mention Tv as I thought the OP could make that leap of
connection by himself...

In the Canon world EV seems to be what everyone else calls "exposure
compensation". In the real world EV is "Exposure Value" which is
basically aperture & speed for ISO 100. (eg: Sunny-16 is EV 15
regardless of actual aperture and speed combo to achieve it).

Your post correctly pointed out that P sets the shutter speed (or
should) to reduce camera shake as well as the other factors I mentioned.

Every time I use a Canon camera I am frustrated by its exposure system
and it takes me many minutes to adjust. Minolta and Nikon is straight
nuts and bolts terminology and usage. Pentax too IIRC.

Cheers,
Alan.

--
-- r.p.e.35mm user resource: http://www.aliasimages.com/rpe35mmur.htm
-- r.p.d.slr-systems: http://www.aliasimages.com/rpdslrsysur.htm
-- [SI] gallery & rulz: http://www.pbase.com/shootin
-- e-meil: Remove FreeLunch.
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