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Thread: Over 2500 images: average focal length = 72mm

  1. #1

    Default Over 2500 images: average focal length = 72mm

    I'm not sure how many here have done this, but I just ran an EXIF data survey on 2500+ images, and found that my photos were shot at an average focal length of 72mm. (115mm w/ 1.6 crop). It was kind of interesting to see where I spend most of my time shooting. Analyzing my photos this way is a good way to guide future lens choices. I'm probably going to put off buying the 10-22mm anytime soon since it will most likely end up collecting dust.

    **I deleted the results of images taken with P&S cameras and only included the images from the D30 and 20D.

  2. #2
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    Not sure how the program works, but from a statisitics viewpoint basing your lens choice simply on the average focal length calculated from your previous pictures seems a little...well...simplistic.

    Don't you want to look at the distribution of the focal length also?

    Take an extreme example. If I have a bipolar shooting habit, such that I either use very wide angle say at 18mm or telephoto range such as 200mm, would the program analyse all the EXIF data and then tell me the average focal length is 105mm?

    Can I then base on that to draw a conclusion that I can to throw away my lenses and buy a 105mm prime instead?

    It is strange to me that you would rely on such a program to tell you your shooting habits. The program will not tell you that your average focal length is 15mm if you don't even own a lens in that range. That does not mean that you should always keep away from wide angle shots right?

    The data is defnitely heavily dependent on the gear you have currently. Why let that limit yourself from exploring different shooting styles?

    Reminds me of an old friend of mine. He swears by the DOF calculation formular and went to the extreme of programming his calculator to compute DOF and he used that for almost every shot. Can you imagine doing an outdoor shoot and telling the model to wait while he calculates the required exposure setting to achieve a certain DOF? I asked him why don't he use the DOF preview and his response was "do you trust your eyes?"
    As complexity rises, precise statements lose meaning and meaningful statements lose precision.

  3. #3

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    Quote Originally Posted by roygoh
    Not sure how the program works, but from a statisitics viewpoint basing your lens choice simply on the average focal length calculated from your previous pictures seems a little...well...simplistic.

    Don't you want to look at the distribution of the focal length also?

    Take an extreme example. If I have a bipolar shooting habit, such that I either use very wide angle say at 18mm or telephoto range such as 200mm, would the program analyse all the EXIF data and then tell me the average focal length is 105mm?

    Can I then base on that to draw a conclusion that I can to throw away my lenses and buy a 105mm prime instead?

    It is strange to me that you would rely on such a program to tell you your shooting habits. The program will not tell you that your average focal length is 15mm if you don't even own a lens in that range. That does not mean that you should always keep away from wide angle shots right?

    The data is defnitely heavily dependent on the gear you have currently. Why let that limit yourself from exploring different shooting styles?

    Reminds me of an old friend of mine. He swears by the DOF calculation formular and went to the extreme of programming his calculator to compute DOF and he used that for almost every shot. Can you imagine doing an outdoor shoot and telling the model to wait while he calculates the required exposure setting to achieve a certain DOF? I asked him why don't he use the DOF preview and his response was "do you trust your eyes?"

    I am sure that itís possible to understand and interpret the results in a much more meaningful way than I did. I used a program called Exifer. Basically you tell it to look at certain files, it reads the image exif data and it spits out a *.csv file. After opening the file in Excel, it looks like a nightmare of a spreadsheet. This particular file had 3200+ rows and 242 columns of data. Again, I'm not an engineer or statistician, so I wasnít exactly sure how to analyze the data. You are right; I HIGHLY simplified the results for one of the columns. I simply inserted an *average* function at the bottom of the column that gave me the focal length info. The exif data came from using the following equipment: 28-135 zoom, 15-30 zoom, 17-85 zoom, 70-200 zoom and a 50 prime.

    Bottom line is youíre right. I shouldnít let this make my gear decisions or shooting styles. Thanks for the slap in the face, it was 1:30am and I was delirious. Good thing Cathay wasnít open at 2am last night; I would have ran out, bought a 72mm lens and sold all my other lenses.
    Last edited by taiwanapurasteve; 23rd March 2005 at 09:41 AM.

  4. #4

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    hey hey steve! been a long time since we last saw you from photoaid, hows life man?

    Anyway you can give me your lens instead of selling them

  5. #5

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    maybe u can create a chart that displays how many shots are taken for each focal length, that might be more accurate on how u use your lens

  6. #6

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    Quote Originally Posted by quekky
    maybe u can create a chart that displays how many shots are taken for each focal length, that might be more accurate on how u use your lens

    Good idea. I'll have to read up on how to use Excel better. I'm sure a pie chart, bar graph or something like that can be done. I'll figure it out and post the info.


    btw- here's a link to Exifer

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    It is still interesting to look at the data and maybe discover something you don't know about yourself.

    You can generate a distribution of the focal lengths in Excel using the FREQUENCY array function.

    Once you have that you can then use it to generate histograms (bar graphs) or pie charts.

    It is probably more interesting also if the subject of the photos can be taken into consideration. For example, analyse the focal length used for portraits and see what focal lengths you tend to use and then ask yourself if you should experiment more with other focal lengths if the data shows a high concentration in a particular focal length range.

    Otherwise you can crunch the data as much as you like and it will not tell you anything useful.
    As complexity rises, precise statements lose meaning and meaningful statements lose precision.

  8. #8

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    Quote Originally Posted by quekky
    maybe u can create a chart that displays how many shots are taken for each focal length, that might be more accurate on how u use your lens

    roygoh: In my immediacy to find a result, I looked for a simple answer. I am sure a more critical look into the focal length of different subject types (portraits, landscape, sports shots) would give me more pertinent information.



    My feeble attempt at creating a chart.

    One more thing to note: Since the exif data contains the camera type I also ran a statistical analysis through the mainframes at MIT, Texas A&M, NORAD and the Pentagon and concluded what kind of camera I need to buy. I used a Canon D30 and a Canon 20D. I added the two cameras and divided by 2 and came out with a Canon 2D5. So now Iím off to CP to go and purchase my new Canon 2D5. Nothing like poking fun at yourself.
    Last edited by taiwanapurasteve; 23rd March 2005 at 11:11 AM.

  9. #9

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    Nice chart... but mebbe you could try changing the Focal Length to the x-axis and the number of shots to the y-axis. make more sense.

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    Quote Originally Posted by RossChang
    Nice chart... but mebbe you could try changing the Focal Length to the x-axis and the number of shots to the y-axis. make more sense.
    Also, it looks like a cumulative chart - it should be a histogram kind of chart, which is more meaningful and helpful in making decision.
    I love big car, big house, big lenses, but small apertures.

  11. #11

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    Quote Originally Posted by smallaperture
    Also, it looks like a cumulative chart - it should be a histogram kind of chart, which is more meaningful and helpful in making decision.
    Okay, okay, I give up. I'm not a numbers freak and have little idea about creating a perfect and meaningful graph. My depth of knowledge on graph creation is strictly limited to the preset options given in Excel. I am more than happy to send anyone the csv file and they can create a more meaningful graph. Small?....Ross? I would be happy to host the new file and insert it in place of the other graph.

    Any takers?

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    A normal distribution curve should give you a better idea.

    Normal distribution curve

    Quite usefull finding

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    Quote Originally Posted by singapurasteve
    Okay, okay, I give up. I'm not a numbers freak and have little idea about creating a perfect and meaningful graph. My depth of knowledge on graph creation is strictly limited to the preset options given in Excel. I am more than happy to send anyone the csv file and they can create a more meaningful graph. Small?....Ross? I would be happy to host the new file and insert it in place of the other graph.

    Any takers?
    PM me the link to your file and I will take a look at it.
    As complexity rises, precise statements lose meaning and meaningful statements lose precision.

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    I like numbers based on the cumulative frequency chart, u took most pics at 28mm focal length, followed by 70, 50, 200, 85.

    The 17-85 would cover your needs ~75% of the time. for the rest, ~20% is covered by the 70-200. so, if you intend to stay on digital, u may need only these 2 lenses. but since u take quite a lot of pics at 50 (3rd highest frequency), keep the prime. A ~70mm prime would only cover u for ~20% of ur shooting so far (assuming u use ur legs to "zoom" a bit).

    u very likely could chuck the 75-300 as it's seldom used.

    But it'll be good to do the analysis based on the type of pics u're taking. I have a list of scenarios (e.g. weddings, fashion shows, travel) and put down the lenses I would usually use for each scenario.
    Last edited by mpenza; 24th March 2005 at 07:22 AM.

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