Exposure time and shutter speeds

<p style="margin: 0in 0in 0pt;" class="MsoNormal"]<span style="font-size: small; font-family: Times New Roman;"]I just noticed that my new 5D Mark II is recording slightly different exposure time and shutter speeds for any one particular shot.<span style="mso-spacerun: yes;"] For example, the EXIF data will show a 1/125 shutter speed and 1/128 exposure time.<span style="mso-spacerun: yes;"] Not that this makes any difference in the real world, but I am curious as to why.<span style="mso-spacerun: yes;"] I noticed my old 30D does not record a difference.<span style="mso-spacerun: yes;"] Any insights?
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<p style="margin: 0in 0in 0pt;" class="MsoNormal"]<span style="font-size: small; font-family: Times New Roman;"]Larry

There are two sets of data that are recorded into the Exif data. One set is the exposure time/F-number, which records the values shown on your camera when you're taking the picture (i.g. 1/320s f/5.6); the other set is the actual value that's been used by the camera. (i.g. 1/332s f/5.7) The camera actually times its shutter speed and record the exact value of the shutter/aperture combination to monitor its own behavior in order to make sure that it's functioning properly. If you try 15s long exposure, the camera will actually do 16s exactly, I guess that's somehow related to its binary system which does not know how to get an odd number for exposure time. I don't exactly know how, but I'm pretty sure that this is normal and it won't affect anything IQ wise.

Something to do with its binary system? Do you have any good reason to say that? Cause otherwise, it doesn't make sense to me at all.

No, i don't. I'm just guessing - that's why i said i don't know how. Would some one be bothered to explain? I'll listen.

<p style="margin: 0in 0in 0pt;" class="MsoNormal"]Hmm, even and odd from the binary system.<span style="mso-spacerun: yes;"] To my meager knowledge, it doesn&rsquo;t matter in a binary system.<span style="mso-spacerun: yes;"] In the photo below
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<p style="margin: 0in 0in 0pt;" class="MsoNormal"]Exposure time = 1/100 sec
<p style="margin: 0in 0in 0pt;" class="MsoNormal"]Shutter speed = 1/99 sec.
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<p style="margin: 0in 0in 0pt;" class="MsoNormal"]The odd/even is reversed from the photo I noted in the original post
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<p style="margin: 0in 0in 0pt;" class="MsoNormal"]Further questions.<span style="mso-spacerun: yes;"] I have now noticed the &ldquo;aperture value&rdquo; and &ldquo;f-stop&rdquo; can be slightly different.<span style="mso-spacerun: yes;"] Huh?<span style="mso-spacerun: yes;"] And, I have now noticed that the exif data shown using Elements 7 says the exposure mode was auto, and I am absolutely certain I had it set on aperture priority.<span style="mso-spacerun: yes;"] That is how I shoot most of my shots.
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<p style="margin: 0in 0in 0pt;" class="MsoNormal"]By the way, DPP gives only shutter speed and aperture value at 1/100 and f4.5.<span style="mso-spacerun: yes;"] It confirms the shot was made with aperture priority,
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<h3 style="margin: 0in 0in 0pt;" class="MsoNormal"]http://roffee.org/experiment_files/I...1_edited-1.jpg</h3>

I have no idea what's going on here.


I can say, though, that a number is a number is a number, regardless of binary, decimal, or hexadecimal. binary 01001101 = hexadecimal 4d = decimal 77 (I think)


I suppose you can use a calculator insteadtrusting me working ona post-it, or just ask Daniel, who probably knows off the top of his head. [:)]

This might be a good question for Chuck Westfall. My 10D doesn't record different numbers, but I know the 40D does record different numbers.

When I look at the EXIF on Flickr for pics taken with my 50D or XSi they both show an increase in target exposure time. Apetures all look the same.


Example: XSi Exposure .003 1\400, Target exposure 1\403


XSi Exposure .002 1\500, Target exposure 1\501


Example: 50D Exposure .01 1\100, Target exposure 1\101


50D Exposure .001 1\1000 Target Exposure 1\1002

Wes, just a wild shot here but what I think you're looking at is that your equipment is manufactured to function within a certain tolerance of the targeted value... with what you posted your worst case is +1% of the target value, which can be considered reasonable accuracy for most applications. It appears your accuracy is a bit better with the higher shutter speeds where you're seeing +0.2% for either body. You should try with a couple dozen shots at various shutter speeds and see what happens. I'd be willing to bet that an average of less than +/- 1% of the target value is simply an acceptable manufacturing tolerance, since you'll never actually notice a difference in the finished product.





Then again, I could be wrong...

IAMB you are most likely correct. Those were just examples of a couple thousand shots and they tend to be in the % you posted. Just kind of strange it reports like that. Doesn't bother me in the least.