M vs AV Mode Metering

[green_photog]

<p>I just did an experiment with my Canon 5D2:</p>

<p>1. Av mode, evaluative metering=1/30 F2.8<br>

2. M mode, evaluative metering=1/10 F2.8</p>

<p>This was done on a white blank wall uniformly illuminated by tungsten light. I chose the same focu point focusing on exactly the same part of the wall. My question is why would Av mode and M mode give me different settings?</p>

<p> </p>

[personalphotos]

<p>Is the EV -/+ set to zero for both images? </p>

 

[green_photog]

<p>Hi Peter, yes, EV set to zero.</p>

[personalphotos]

<p>If the camera was in the same metering mode, the camera didn't move and the light didn't change, then I don't know what is going on. </p>

[john_deerfield]

<blockquote>

<p>white blank wall uniformly illuminated by tungsten light</p>

 

</blockquote>

<p>Can you post the picture? A uniformly lit white wall is pretty tough to do! With that in mind, I would certainly be using the same focus point AND a tripod, otherwise, you don't <em>know</em> if you are picking the same exact point on the wall (if it's a white wall, what's your target?!). And I would set the white-balance to tungsten: lock down as many variables as possible. </p>

<p>All that said, when handholding a shot, I can see two-thirds to a one-stop difference when I am in class. But almost two stops is a lot. Also keep in mind, you have just discovered the value of an incident light meter. TTL can be fooled, it isn't perfect. Not that you MUST use a light meter, but you have discovered the value of one.</p>

[picturesque]

<p>Did you have the flash mounted and on? If so, it is probably NEVEC. If not, don't know. :^)</p>

[Marcus Ian]

<p>We haven't seen enough data yet to present a plausible hypothesis (other than outright guesses).<br>

In addition to the questions already asked, I'd ask a few more:<br>

What did the images look like?<br>

Was it the same lens? What lens?<br>

If it was a zoom, was there any change in focal length?</p>

 

[jody_stowitts]

<p>Are you sure you don't have 1/3 stop + or - set from a previous shoot on one of the modes? Could be also that camera displays different fractions of EV in the two different modes. Or, light changed just a bit between the two exposures. If all else fails diagnostically, pick which of the two exposures you like the best and "go with it". One third of a stop is also probably within acceptable parameter going from mode to mode If no settings error, my guess is the second instance. The AV mode, remember, is "stepless--i.e., the shutter speed is much more finely divided than just 1/3 of a stop. Y our AV shutter speed could have been 1/17 of a second or so, and the "closest fraction" is used to represent that speed on the display.</p>

[dan_south]

Question 1: What ISO value were you using?

 

Question 2: Please clarify what you mean by "gave you" different settings. What did M mode give you? And how did you determine the exposure in M mode?

[green_photog]

<p>Thank you for all your responses. I found the culprit, last night I had the Pocket Wizard attached to my hot shoe when I did that experiment. Without flash attached, Av, Tv and M mode all give the same exposures (when the exposure needle in the center).</p>

<p>However, with a flash attached to the hot shoe and turned on, the M exposure is exactly 1 stop slower than the Av and Tv exposures.</p>

<p>For example, Av and Tv = f2.8 1/200. M=f2.8 1/100. This is done using a 35mm prime focusing on a off white bedroom wall illuminated by tungsten light bulb. I think Av and Tv expose for the ambiance and M is not so maybe that's why there's some differences in the exposures. Looking at the JPG, I think the slower M exposure results in better picture.</p>

<p> </p>

[sherman_peabody]

<p>Well, in M the shutter speed is one stop slower, but the exposure is therefore one stop greater.<br>

Yes I think this is typical behavior and done on purpose. On a non-5D2Canon camera with a popup flash, the exposure in Av mode will be one stop less when the flash is popped up than when it isn't. I think this is in recognition that the flash, even as fill, will be adding some light even to the background. At least my XT did that, and I haven't checked it, but my T2i probably does too. But of course in M mode, it just shows you the actual reading whether a flash is present or not.</p>

<p>So if you stay in Av mode on your 5D2, you should get a one-stop difference in exposure depending on whether something is in the hot shoe, all else being equal. I think that's completely normal for Canons.</p>

 

[michael.gregory]

<p>I think that you will find that the Shutter synchronization range for flash is between 1/30 and 1/250 second. If you have a flash attached the 5D2 will default to a shutter speed somewhere in this range. At speeds slower than 1/30th there is significant risk of a blurry image due to subject motion being partially illuminated by ambient light. In manual mode the photographer the flash does not set a shutter speed upper or lower bound and the photographer has full creative control of the camera and the flash. The difference in metering will change if you change your composition, but there will still be a difference almost every time.</p>

 

[zack_zoll]

<p>Good answer, Michael.</p>

[picturesque]

<p>As I said, look up NEVEC.</p>

<p><a href="http://eosdoc.com/manuals/?q=NEVEC">http://eosdoc.com/manuals/?q=NEVEC</a></p>

<p>The difference will vary according to the ambient light levels, not just 1 stop.</p>