EXIF question: EV and Distance

[dinora_de_rivera]

<p>I am looking at some EXIF data and I see something like</p>

 

<blockquote>

<p>1/100, f/5.6, ISO 100, +0.3 EV.</p>

</blockquote>

<p>So what I'm wondering is if I'm in aperture mode, then the camera adjusted either the shutter speed or the ISO. Which one did it change? And is what is written in EXIF what is the final version of parameters or are the values the uncorrected ones?</p>

<p>Another question is about the parameter of distance, which some files have. One shows 11.9 m, the other -1.0 m. What does it tell? How do you focus on 11.9 m or -1.0 m? I presume the last one is hyperfocal distance, but the first one baffles me.</p>

<p> </p>

[mark_sirota1]

<p>The values written are the final values.</p>

<p>Whether the camera adjusted shutter speed or ISO is not recorded, but every camera I've seen will adjust shutter speed in this case.</p>

<p>For the last, what EXIF field(s) are you talking about, and what EXIF viewer are you using? The fields are called SubjectDistance and SubjectDistanceRange. The former is the distance to the subject in meters, the latter is simply 0, 1, 2, or 3 which translate to "unknown", "macro" (<1m), "close view" (1-3m), and "distant view" (>3m).</p>

<p>There are also GPS-related fields, GPSDestDistanceRef and GPSDestDistance. The firmer indicates the units (kilometers, miles, nautical miles) and the latter is the distance in those units.</p>

<p>Different EXIF viewers may display these fields differently, but I don't see any where -1.0m would be a sensible value.</p>

[lex_jenkins]

<blockquote>

<p>"Which one did it change?"</p>

</blockquote>

<p>Depends on the camera and settings. Some cameras, in full auto-everything mode including auto ISO, may adjust the ISO to accommodate exposure compensation. For example, in aperture priority mode with auto-ISO enabled and the camera set to limit the slowest shutter speed, dialing in exposure comp will adjust the ISO before it chooses a slower shutter speed. I tend to set the slowest default shutter speed to 1/60th, the slowest I can reliably handhold. Auto-ISO adjusts to accommodate the lighting at the default metering and with my exposure compensation adjustments. Once the maximum ISO is reached, then the camera will force a slower shutter speed.</p>

<blockquote>

<p>"And is what is written in EXIF what is the final version of parameters or are the values the uncorrected ones?"</p>

</blockquote>

<p>In my cameras, the metadata shows the actual exposure data, including when exposure compensation is used. However the EXIF data doesn't reveal whether the camera chose to apply the exposure compensation to the aperture, shutter speed or ISO. That might be useful info. But I just run some quick tests to determine how my cameras tend to adapt to exposure compensation so I'll have a rough idea of what to expect. If I'm concerned about high ISO noise I'll set the ISO manually so the camera will force either aperture or shutter speed adjustments to accommodate exposure compensation (depending on whether I'm shooting in program, aperture or shutter priority mode).</p>

<p>No idea about the distance metadata, I've never really paid attention to that.</p>

[Andrew Garrard]

<p>I'd guess "-1m" was focussed at infinity, but I could be wrong. Otherwise, it'll be the distance between the camera and the plane of focus (though whether it's from the camera's film/sensor plane or from the lens nodal point I couldn't tell you without checking). The lens doesn't focus on an object - there's a plane that's some distance from the camera, and any subject that is positioned on that plane will be in focus. Effectively, it's where the image of the sensor is projected into space by the lens.<br />

<br />

As for shutter and ISO, my experience is that cameras normally let you specify that one changes before the other. Can you deduce what happened from the camera settings? [Edit: As Lex suggested.] I'm not sure that the ISO would say <i>why</i> some settings were so, just what they are.</p>

[keith reeder]

<p>Andrew might well be right about -1m, but it's equally likely that it's camera shorthand for "<em>sorry, I haven't a clue</em>" - distance to subject Exif is notoriously unreliable, especially if third party lenses are involved, but in my experience it's often wrong with Canon lenses mounted to Canon bodies too.</p>

<p>In fact it's a source of amusement to me that Photo Ninja, my favourite Raw converter, will report a distance to subject, followed by the word "<strong><em>guess</em></strong>"!</p>

[mark_sirota1]

<p>The Exif specification does have a way to specify infinity and unknown, but that doesn't mean that cameras or Exif readers are handling it according to the specification. (SubjectDistance is recorded as a ratio; numerator=0 means unknown, numerator=0xFFFFFFFF means infinity.)</p>

[dinora_de_rivera]

<p>I was using FastPictureViewer and it just says "Dst".</p>

[mark_sirota1]

<p>Try using something else -- <a href="http://regex.info/exif.cgi">here's an online one</a>. See what that says for the same file.</p>

[dinora_de_rivera]

<p>It says nothing.</p>

<p>I want to ask something about white balance and altitude in the GPS data: if it says both manual and cloudy, is it manual or cloudy? Preset or really manually set, but in the range of cloudy? The GPS altitude is the altitude above mean sea level?</p>

<p>Does Jeffrey's Exif Viewer keep the images on his server or only temporarily and deletes them?</p>

[mark_sirota1]

<p>WB: Not sure. What fields are we talking about?</p>

<p>Yes, altitude in GPS terms is altitude above sea level.</p>

<p>Jeffrey's viewer does not store the file.</p>

[mark_sirota1]

<p>I looked up white balance in the EXIF specifications.</p>

<p>The tag WhiteBalance can be 0 for auto or 1 for manual.<br>

The tag LightSource is also an enumeration with the following possible values:</p>

<ul>

<li>unknown</li>

<li>Daylight</li>

<li>Fluorescent</li>

<li>Tungsten</li>

<li>Flash</li>

<li>Fine Weather</li>

<li>Cloudy Weather</li>

<li>Shade</li>

<li>Daylight Fluorescent (D 5700-7100K)</li>

<li>Day White Fluorescent (N 4600-5500K)</li>

<li>Cool White Fluorescent (W 3800-4500K)</li>

<li>White Fluorescent (WW 3250-3800K)</li>

<li>Warm White Fluorescent (L 2600-3250K)</li>

<li>Standard Light A</li>

<li>Standard Light B</li>

<li>Standard Light C</li>

<li>D55</li>

<li>D65</li>

<li>D75</li>

<li>D50</li>

<li>ISO Studio Tungsten</li>

<li>Other</li>

</ul>

<p>So assuming these are the fields you're seeing, it was probably set manually to the "cloudy" setting.</p>