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Thread: Dragonflies

  1. #21
    Join Date
    Dec 2007
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    1,760
    you can get picasa3 from google free...even works on raw pics

  2. #22
    Join Date
    Mar 2005
    Location
    Cambridge, UK
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    686
    Been out 2 hours, broken my sunglasses by riding over them, bitten by a swan and seen 1 dragonfly that kept landing on a reed over the lake about a meter away

    Spoke to a fisherman and he said that he had only seen one or two all morning.

    I will take a look at picasa3 SONYNUT as I am posting more photos these days and my website is getting full of other things.

  3. #23
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    Mar 2005
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    Cambridge, UK
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    Went out again but later today - no improvement on sharpnes.

    Similar distance on these and about the same size crops. Took about 50 photos at different settings ( no filter ) and I was not happy with any of them.

    AF point on all of them was on the body just behind the eye.

    Think I will take my A650 out later and see what I get from that.

    ISO200 F11 1/50


    ISO200 F14 1/25


    ISO400 F11 1/100


    ISO200 F11 1/250
    Last edited by Anthony; 07-23-2010 at 02:55 AM. Reason: Added EXIF data text

  4. #24
    Join Date
    Nov 2008
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    Monmouthshire, UK
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    2,152
    Do you have a back focus issue?

  5. #25
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    Mar 2005
    Location
    Cambridge, UK
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    I have looked into Back focus and carried out a test:

    ISO100 F5.6 55mm 1/640


    ISO100 F11 55mm 1/160


    The front of the lens was roughly 0.5m from the center point.

    I had assumed that the lens DOF was a 1/3rd in front 2/3rd behind.
    It looks on the original CR2 images that it is about equal in front of and behind.


    Focus test/
    To use the chart you set it up at 45 degrees to the axis of the lens as shown below. In this configuration (at 45 degrees) the 1, 2 and 3cm marks are correct. They are actually spaced at 1.41, 2.82 and 4.23cm from the focus line, but when viewed at 45 degrees these distances are modified by the Cosine of the viewing angle (Cos 45 = 0.707).
    Last edited by Anthony; 07-23-2010 at 08:17 AM.

  6. #26
    Join Date
    Nov 2008
    Location
    Monmouthshire, UK
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    2,152
    Quote Originally Posted by Bonzo View Post
    I have looked into Back focus and carried out a test:
    [IMG]
    [IMG]
    The front of the lens was roughly 0.5m from the center point.

    I had assumed that the lens DOF was a 1/3rd in front 2/3rd behind.
    It looks on the original CR2 images that it is about equal in front of and behind.
    Focus looks OK.
    Some people don't like that test method. See this thread.

    The DOF 1/3..2/3 rule of thumb doesn't work at higher magnifications when it's more like 50/50.

  7. #27
    Join Date
    Mar 2005
    Location
    Cambridge, UK
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    686
    Using the alternative test the results look similar in fact I would say there was slightly more in focus at the front than the back.

    F5.6


    F11


    All I can put it down to is operator error ?
    But its strange I get the same effect on every image and the area that I am focussing on - body - is still not great and at F11 it should have been spot on.
    Last edited by Anthony; 07-23-2010 at 09:46 AM.

  8. #28
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    Nov 2008
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    Monmouthshire, UK
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    Well, the images certainly seem to be back focused even though the test belies that.
    Maybe the image sensor is displaced to one side and you're not focused where you think you are. I'm assuming you were using the centre focus sensor.

  9. #29
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    Mar 2005
    Location
    Cambridge, UK
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    Yes I was using the center focus sensor and I was focusing on the body area behind the eye on 3 out of the four above. But that is a good point: how big is the focus area - how accurate is it with the spot and box on the display with the sensor was there enough contrast on that area.

    AF point on one of the images:


    Perhaps I should have used the wings as the focus point which looking back on it I did on some of the first photos I took. The first image I posted looks a lot sharper than any of my latest ones.

  10. #30
    Join Date
    Nov 2008
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    Monmouthshire, UK
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    How big is the focus area? I don't know I don't have (never did) a Canon.

    If you tape a strip of paper to a window, you can slowly pan the camera towards the edge of it until it decides to acquire focus. That will give you an idea of where the sensor actually is in relation to the centre markings.
    Last edited by Peekayoh; 07-23-2010 at 10:57 AM. Reason: apelling

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