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The Fairy Tale about Learning from Exif

People often ask for the Exif data or settings in forums and groups, which is quite understandable on one hand, that you want to know how a photo was made. One part of that story is the Exif meta data.

Exif Logo

Furthermore there is hardly anyting secret in the Exif. Therefore, to me, it is not understandable why some photographers are reluctant to disclose their Exif data. Some of the meta data may well be private, like the real name, serial numbers, gps position and exact date and time. So on the other hand it is understandable, that photographers strip off the Exif before digitally publishing photos. But the settings? What is secret about the settings?

However, if a group has  a rule in place, or just common habit, to publ ish the settings along with the images, then I strongly suggest to tell the full story about creating the photograph, so that people can really learn something. Further down in this article I describe what I mean by that, although I do not beleive that this list is remotely complete. You might be surprised how few information is in the Exif and what else is crucial to understand the making of the little peace of art that you are interested in. I bet you'll never ask for Exif alone again.

In parallel you will understand how handy Exif may come when trying to find any mistake, that you or others may have made. So when ever you'll ask for assistance in a forum of any kind, don't forget to post or link the image in question in full resolution, as it came out of the camera, along with all relevant Exif data. (ExifTool can be helpful to wipe out only those metadata that you do not want to share.)

About Exif

Exif is a standardized data structure for saving meta data along with the image information within the same file. Exif is supported for JPEG, JFIF, PNG, TIFF, lots of RAW formats, and more.

Amongst other information in Exif is stored the aperture, exposure time, film/sensor speed, focal length, distance to the subject (focal pane), camera model and brand, serial numbers, shutter count, geo position, ...
Not included in the Exif standard but often provided in proprietary format embedded in the manufacturers notes section of Exif is the lens, its serial number, firmware version and more settings that may or may not be part of the official Exif standard.

Exposure

Aperture

The aperture is usually a disk, made of several blades, that form a hole in the middle, a hole of variable size. The hole's diameter is crucial for the amount of light that passes though the lens within the exposure time. The standardized aperture value, e.g. f/2.0, is a relative value. 2.0, which stands for the factor 1/2.0, means that the (average) diameter of the hole is half of the focal length.

Exposure

(d/f = aperture value, f - focal length, d - diameter of the hole in the aperture)

As important for the perfect exposure is the exposure time and the film/sensor speed. If you now take the same ISO value, time and aperture that some other photographer used for the photo you like, then you may get the same result only - and only - if the light set/situation is exactly the same. Same type of the day, same weather, same lamps, same intensity of flash lights, same softboxes, reflectors, etc. pp.

It is just ... all of that is not included within the Exif data.

Exposure Value

Combinations of aperture and exposure time (but not ISO) stand for an exposure value (EV). All combinations of these values, that create a similar exposed result in the given light situaion with the same ISO, are associated to the same exposure value. E.g. EV 12 stands for f/5.6 at 1/125s. Or f/4 and 1/250s. Or f/8 and 1/60s. So what you really need to know is this not even included in the Exif file.

Depth of Field

Besides its importance for the exposure does the Aperture influence the depth of field (DoF).
When fockussing on the main sujet everything with the same distance to the camera is sharp alike, that is the focal pane. With a small depth of field only milli- or centimeters before and after the focal pane is sufficiently sharp. The further an object is away from the deptht of field, the more blurry it will be in the image. With a small depth of field this blurriness grows rapidly with the distance of the sujet from the focal pane.
With a large depth of field it is the opposite. When the depth of field lasts from some minimal possible distance to the horizon, for a given aperture, then we speak of the hyperfocal distance.

The depth of field is smallest with the aperture wide open and it is maximized with the aperture closed to its maximal extend.

You might think now that an image gets sharper the further closed the aperture is. Unfortunately it is not that simple.

Diffraction

When the hole in the aperture gets smaller, the diffraction gets stronger. The diffraction causes some increasing blurriness overall on the picture, regardless of the distance of the object. So by closing the aperture you do gain sharpness where you want it to be but you loose some sharpness overall.

Well, there is more that influences the depth of field.

Film/Sensor format

Long story short: The smaller the film or sensor format is the deeper is the field of sharpness. An f/11 on a medium format camera does produce significant smaller DoF than an image with the same perspective and view angle on an MfT body.

For more details on this effect refer to my article "Sensor and Depth of Field"

Well, there is more that influences the depth of field ...

Reproduction Scale

It is not only the aperture but the focal length and the distance, that influences the DoF. Focal length and distance combined care for the reproduction scale. That is the scale in which the image of the sujet is projected onto the film or sensor. The larger this scale is, the smaller the DoF is. Macro photographers suffer from that strongest.

And the reproduction scale is not part of the Exif. In most cases modern cameras do include the distance to the sujet in focus within the Exif. You might be able to calculate the reproduction scale from that information or use one of the DoF calculators in the web.

Exposure Time

The exposure time is the third factor in the magical triangle of ISO, aperture and time. It is as easy as that: The longer the film or sensor is exposed to the light that comes through the lens, the more light arrives on the sensor pane, the brighter the image is. (and vice versa)

Furthermore the time may does have some impact on how the image looks like. Things in motion may appear blurry with longer times. Well, when the sujet in motion is moving towards the photographer or in the opposite direction, then this effect is much smaller than any motion in 90° to the photographers direction of view. You may see or guess this from the image. However, that information is not included in the Exif data, too.

A handheld photo shot will likely look shaken when the time is too long. Very short times may have other unwanted effects. 

Be honest to yourself: Somebody who can take all that information out of an image by looking at it, does not really need the Exif data to kinda produce similar results.

Flash and Exposure Time

It gets even more complicated when the photographer uses flash lights. When the flash is the only or dominating source of light, then the effective burn down time of the flash light is most important, not that much the exposure time given in the camera. (Unless HSS sync was used - just to add more complexity.)
In some cases the Exif contain information about the flash being used. However, when external flashes are used, no eTTL/I-TTL etc, then the Exif contain the wrong information that no flash was fired, just because the camera does not "know" about it. Exposure time is then likely a common Sync-Time from 1/60s to 1/250s.

Most important for the image is then, how many flashes have been used, where they were positioned, how far away, settings on the flash, softboxes etc.

None of that is - usually - contained in the Exif data.

Again, if you can "read" all of that out of the image by looking at it, then you don't need the Exif at all.

Speed and noise

 

 

Well, finally the ISO setting must be important so that you can learn from that. You have read and understood already, that the color noise in the image will get worse the higher the ISO setting is. (Exception are LOW-Settings like 50 ISO on a camera that normally supports 100 ISO)

 

I don't want to stress my opinion about the importance of noise of modern digital cameras here because I already wrote about that aspect.

 

How much the noise actually raises with ISO values depends very much on the camera make. Older and cheaper camera models tend to make more noise. (Just a rule of thumb)

 

So far so good. The ISO is usually given in the Exif and it is correct.

 

However, the artists may have used some de-noising software, either in the post processing or already provided by the camera's firmware, so build-in. Exif may give a hint about de-noising techniques used within the body (data varies from manufacturer to manufacturer and may not be read our properly by 3rd party Exif readers).
The Exif does not give any hint whether de-noising stuff was used in the finishing.

 

Expose to the Right and Noise

 

The Exif does not tell anything about the photographer using the Expose-To-The-Right (ETTL) method. With this method an image is over exposed and darkened in the finishing, if the image contrast allows for that. It is the nature of the signal noise that it appears relatively strong in the darker areas of the image. By over exposing the shadows, without the lights burning out, the photographer moves the whole histogram (all tones within the image) to the brighter side / right side of the histogram. By darkening that image later the noise within the shadows gets significantly flattened, nearly removed in the best case.

 

So finally we have to take ISO (ASA, DIN respectively) off the list of useful Exif data.

 

Bracketing (HDR, Stacking)

 

Perfectly useless are Exif when it comes to bracketing of any kind. HDR increases the dynamic range significantly and can be used to reduce the noise. (Could be used for the opposite though :-) ) Focus stacking is a method to extend the DoF with macros well beyond the physically possible.

 

In the best case the Exif contains the exposure values of one of the images of the series. Which one is rather random.

 

Some maker include more information about the bracketing series within the non-standard manufacturer details, which is hardly supported by 3rd party Exif readers. And it is only contained in the case that some build-in bracketing/HDR-function was used, but not when the photographer does the bracketing manually.

 

This information, and the "why", you can really get by asking the photographer only.

 

Hardware

 

Focal length

 

Now we are getting closer. There is hardly any setting or lens characteristic respectively more important for the image as the focal length along with the perspective. Along with the sensor/film format, you can take from the focal length which field of view (angle) the image was taken with. (Only of course if the photographer did not cut the image, because cutting effects are not stored in Exif)

 

The good part is that the focal length is usually quite reliable and contained within the Exif. Unless, of course, when the photographer uses some manual lens. And the perspective is rarely contained in the Exif. Sometimes the GPS data is accurate enough to provide you some information about where the picture was taken in outdoor situations. However, you cannot know if and how accurate it is - if contained at all.

 

I am not going to stress the crop factor in this article. You can get an impression of the various common sensor/film formats in this blog post and see, which different angles the same focal length can produce when attached to different bodies.

 

You might have guessed already, that neither, the field of view nor the sensor format is stored within the Exif data. You could go for the camera model and then google it sensor size. But again, the image may well be cropped, either in the finishing or already within the body itself. (APS setting on full frame bodies, digital zoom on some compact cameras and mobiles, ... )

 

Alright. So the focal lengt is off the list, too.

 

Body

 

As described above, the information about the body may well be interesting in combination with other data. However, please do not remotely think, that you can simply make the same nice photograph by buying the same body and lens. :-)

 

Lens

 

Fact is, that the lens influences the overall quality far more than a body can do. Problem is, information about the lens being used is NOT part of the Exif standard. It is, however, usually stored within the manufacturer notes, but some Exif viewers are not exactly good at determining the correct lens, especially when the lens is from some 3rd party manufacturer. And that is not the programmer's fault. The information about lenses being used is sometimes ambiguous.

 

The lenses quality issues may well be reduced with editing software. There are - sometimes even build-in - tools available to fix a lenses diffraction, vignetting and even chromatic aberration. The same applies to the overall sharpness.

 

Therefore the lens is off the list of useful information. (Exceptions apply)

 

Filter, Hood

 

Filters are mean to those who want to learn from Exif. Although they can be quite destructive, especially Sky-, UV- or protect-fiters, some may well be useful and have some significant impact on the image. Such as Polarizers, grey (ND) filters or even graduated ND.

 

A hood does not influence the image in the best case. It may well add significantly to the contrast, and therefore to how sharp an image appears to be, and to the reduction or removal of lens flares.

 

And the problem is: Nothing of that will ever make it into the Exif data.

 

Tripod, Monopod

 

Needless to explain in detail, how important tripods and monopods can be. Needless to explain, that the Exif data does not give a clue about the usage of tripods of any kind.

 

Post Processing, Finishing

 

Typical process steps are the white balance, contrast, saturation, brightness, - even partly - , noise reduction (as discussed), reduction or adding of vignetting, ...

 

Some of that stuff is already done within the body. And more. Such as picture styles, HDR, even focus stacking. If done within the body then the Exif may give details about hat - given that your Exif viewer does read well the non-standard manufacturer notes.

 

Conclusion

 

Talk to the photographer. Don't even look at the Exif. Don't ask for Exif nor settings. Just ask how the image was taken. You will certainly learn from the anwser - if given - and you will learn about the important stuff, that what really matters.