Exposure time and shutter speeds

[TheRoff]

<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?
<p style="margin: 0in 0in 0pt;" class="MsoNormal"]<span style="font-size: small; font-family: Times New Roman;"]
<p style="margin: 0in 0in 0pt;" class="MsoNormal"]<span style="font-size: small; font-family: Times New Roman;"]Larry

[Benjamin]

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.

[Oren]

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.

[Benjamin]

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.

[TheRoff]

<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
<h3 style="margin: 0in 0in 0pt;" class="MsoNormal"]<o:p></o:p></h3>
<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.
<p style="margin: 0in 0in 0pt;" class="MsoNormal"]<o:p></o:p>
<p style="margin: 0in 0in 0pt;" class="MsoNormal"]The odd/even is reversed from the photo I noted in the original post
<p style="margin: 0in 0in 0pt;" class="MsoNormal"]<o:p></o:p>
<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.
<p style="margin: 0in 0in 0pt;" class="MsoNormal"]<o:p></o:p>
<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,
<h3 style="margin: 0in 0in 0pt;" class="MsoNormal"]<o:p></o:p></h3>
<h3 style="margin: 0in 0in 0pt;" class="MsoNormal"]http://roffee.org/experiment_files/IMG_012101101_edited-1.jpg</h3>

[Colin]

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. [:)]

[ShutterbugJohan]

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.

[Wes]

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

[IAMB]

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...

[Wes]

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.