Same settings, different result

Discussion in 'Photography Beginners' Forum' started by eagledad, Feb 24, 2020.

  1. eagledad

    eagledad TPF Noob!

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    Out taking shots along the ocean at a lighthouse last Saturday with a Canon 7d. I took two photos of the same shot, in aperture priority mode, using f20, iso400, 30 mm focal length, -0- exposure compensation, and in one the camera selected 1/80 shutter speed, which was heavily overexposed, and the second it chose 1/250th, which provided a nice photo. I made no changes to the metering settings on the camera. Is there an easy explanation for this?


     
  2. SquarePeg

    SquarePeg hear me roar Staff Member Supporting Member

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    What type of metering at you using? If spot then you may have moved slightly and spotted on something dark increasing your exposure needs and slowing the ss selection.
     
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  3. SquarePeg

    SquarePeg hear me roar Staff Member Supporting Member

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    And may I ask...f/20? What were you trying to achieve?
     
  4. eagledad

    eagledad TPF Noob!

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    Evaluative metering
     
  5. eagledad

    eagledad TPF Noob!

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    A good question. I chose the "beginners" forum because I struggle answering questions like this. I"m all ears though.
     
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  6. Soocom1

    Soocom1 Been spending a lot of time on here!

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    Depends on the shot and location.
    if possible I would post both photos to view so we can determine whats going on.

    As for F20, if its set to auto, the camera will adjust the aperture to whatever it wants because if automatic, the lens has no real stepping involved.
     
  7. vintagesnaps

    vintagesnaps Been spending a lot of time on here!

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    Was it really sunny? If it was, and you were near water which was reflecting sunlight, the camera may have been trying to adjust because of the 400 ISO. That much light sensitivity in sunlight is too much (an ISO of 100/200 would be more likely). So the camera may have readjusted trying to set a combination that would work. At 400 the 1/80 of a second shutter speed may have been too slow, and let in light for too long so it was overexposed. So the 1/250 would've cut back on the amount of light.

    That f20 is a really small aperture and a somewhat unusual setting. Usually most photos are probably more midrange in aperture, closer to f11 to f4 for many light conditions. I shoot with manual settings, I'd usually use a smaller aperture like f16 if it's bright and sunny. (The aperture numbers are fractions, so the f16 is 1/16 of the focal length, f8 is 1/8th, f2 is 1/2, etc.) A larger aperture like f2 is going to have the lens more open and let in more light.
     
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  8. Original katomi

    Original katomi TPF Supporters Supporting Member

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    At f 20 you are going to get diffraction and it will make the image soft. You don’t say what lens, so I would suggest you look up the reviews on it and find what is called the sweet spot as others have said this is often around the f8 to f16.
    I have just run your camera on an app I have and at f20 you are into the red as far as diffraction is concerned.
    A crude explanation of diffraction is that light rays spills over the edges of the photo cells. Have a look on the web for more detailed and correct explanations
    For reference the app is from Martin Bailey photography
    Photographers friend
     
  9. Derrel

    Derrel Mr. Rain Cloud

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    A very slight change in framing might have been enough to cause the evaluative metering to set 1/250 of a second for your second photo....if there were specular highlights on the water, that could have played a factor. 1 /80 to 1/250 , is not "that" much of a difference.
     
  10. Original katomi

    Original katomi TPF Supporters Supporting Member

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    E72A3F21-9107-40E9-BCE1-42DB4638B6FC.jpeg I do panaramas, often requiring 20 or more shots. I learnt the hard way that on any of the semi auto settings that a simple thing like a bit of cloud can alter exposure.
    As you are digital, when you next have chance, go out and take 20 shots on AV , 20 on TV and on 20 in manual using an average setting from either of the first 20.
    You can pan round or use the same spot.
    Later look at the images and read the exit data, see what you think, and please let us know. If iam talking out of my
    Behind, well let me know that as well.
    Digital means as photographers we can experiment, try ideas and worry less about the cost of processing, with the bonus of having the info about the pics in our hands not relying on hasty scribbled notes.
    For example this image is the result of nearly 90 attempts, making adjustments until I achieved this result E72A3F21-9107-40E9-BCE1-42DB4638B6FC.jpeg
     
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  11. Original katomi

    Original katomi TPF Supporters Supporting Member

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    073444F0-7AAA-4D1F-874D-916BF170F558.jpeg
    This is an earlier attempt straight out of camera, at this stage I was still altering strobe frequency, output power
    And finding focus point in near darkness. The plastic work man sign is focus point, I had to try and aim coins at it using just the light from the flash and remote trigger LEDs
     
  12. SquarePeg

    SquarePeg hear me roar Staff Member Supporting Member

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    The reason I asked why you chose that aperture is because I was wondering sincerely what you were trying to achieve with the photo. If you’re taking a typical landscape scene and there’s no special circumstances then I would agree with what is posted above F 11... F-16 maybe. If you were trying to do something with motion and the waves then maybe you would need a longer shutter speed so you might have to adjust your aperture accordingly to let in less light.

    I don’t use aperture priority very often. I like to choose aperture and shutter speed. If you’re not sure what settings to choose and you’re not trying to achieve a certain look like shallow depth of field or motion blur the I found a good learning technique when I was starting out was to take a photo in full auto mode and look at the settings and figure out what I needed to change to get the look I wanted and then adjust aperture and shutter speed from there.
     

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