EC and Shutter Speed

[riz]

<p>Suppose I am in Aperture priority mode and I increase Exposure Compensation, by doing this my shutter speed will decrease and let more light to come in. My question is, is there any benefit of using +EC in the Aperture Priority mode?</p>

<p>And how can I avoid camera changing the values of Shutter Speed and Aperture on changing the EC value.</p>

<p>Thanks in anticipation,</p>

<p>Riz</p>

[bueh]

<blockquote>

<p>My question is, is there any benefit of using +EC in the Aperture Priority mode?</p>

</blockquote>

<p>Absolutely! It's what we all do! Only rarely there is a scene that is "medium grey" as the reflective light meter sees it.</p>

<blockquote>

<p>And how can I avoid camera changing the values of Shutter Speed and Aperture on changing the EC value.</p>

</blockquote>

<p>Uh, what would be the point in using exposure compensation if not to change the amount of light hitting the sensor? Or do want to have something like "ISO priority"? Some cameras have a mode like this, check your manual if yours has it, too.</p>

[tommyinca]

<p>"In there a benefit in Exposure Compensation in A mode?"<br>

One example is for backlight situation. You may want to dial in some +EC to lighten up the subject if thats what you want. Another is where the background is snow or ice, some +EC may be needed to make then look like what they are. Or if the background is total darkness or use of spot lighting some -EC will help.</p>

<p>"How to Apply EC without changing shutter or priority."<br>

ISO vaule is another control you have beside shutter speed and aperture. You may be able to trick the camrea let you doing that with autoISO. But then, it is a lot easy to do M manual metering and also changing ISO. </p>

<p> </p>

[andrewg_ny]

<p>Adding +EC by definition is a request to effectively increase the exposure. This can be done only three ways: longer shutter duration, wider aperture, or increased sensitivity (ISO).</p>

<p>On a film camera, sensitivity was fixed with the film loaded, so the only way to increase exposure with Av (aperture priority) mode is to increase the shutter duration.</p>

<p>On a digital camera, the sensitivity can be adjusted from shot to shot; so in theory you could fix the aperture and shutter and increase sensitivity in response to a request for greater exposure.</p>

<p>How this can be done depends on your camera. On some, it may not be possible. The most straightforward implementation of this that I'm aware of is on Pentax; several of Pentax's more recent digital SLRs include a "TAv" mode, where shutter and aperture are given priority (fixed) and ISO is changed to provide 'correct' exposure. In this case, exposure compensation would only cause ISO to change. Alternatively, some cameras (maybe some Nikon?) may also allow 'Auto ISO' to be enabled in Manual mode. If you can enable auto ISO in manual mode with your camera, I would expect it to behave roughly like Pentax's TAv mode; I think many cameras do not allow this however.</p>

[dbcooper]

<blockquote>

<p>"My question is, is there any benefit of using +EC in the Aperture Priority mode?"</p>

</blockquote>

<p>Yes - it's the only way you can vary exposure (i.e. lighter or darker).<em> In Aperture-priority mode</em>, the camera (and not you) automatically sets the shutter speed to agree with the camera's internal light meter reading; the lens aperture is 'locked' in per your selection.</p>

<p>You could vary the shutter speed by changing ISO, but since the shutter speed is varied to agree with the camera's internal meter using your aperture selection, even though the shutter speed would change, the overall exposure would remain the same.</p>

<p>The only way to vary the exposure would be to use the Exposure Compensation control.</p>

[bebu_lamar]

<p>The short answer is YES there is benefit and NO there is no way to change the EC setting without changing either aperture or shutter speed.<br>

But here is the long answer. The term Exposure Compensation is often misunderstood by people who started out using a camera in auto exposure mode. Exposure compesation really means biasing the meter so that the camera would make a different setting in exposure by changing either shutter speed or aperture or both. Is there any benefit? It allows you to change the exposure (by changing aperture of shutter speed) from that set by the meter in auto mode. However, I never use this feature because it's much easier and faster for me to simply switch to manual mode.<br>

For the second question the only way to change the amount of exposure on your sensor without changing either shutter speed and aperture is changing the amount of light on your scene (i.e. put some more light on your subject). You can get a brighter or darker image by changing the ISO sensitivity setting but this does not change the amount of exposure given to the sensor. Without changing the subject brightness, aperture or shutter speed the amount of exposure doesn't change. However, with the same amount of exposure you can tell the camera to adjust the gain from the sensor when it does the readout by changing the ISO setting.</p>