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Should the Canon 28-105mm f/3.5-4.5 USM II lens report focal length information to a Canon 430EX II flash?


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<p>Sometimes, my Canon 430EX II flash recognizes the focal length being used on my Canon 28-105mm f/3.5-4.5 USM II lens, and sometimes it does not.<br>

<br /> <br /> Does this mean my flash is somehow defective, some contact isn't always being made, some setting has been incorrectly adjusted, or something entirely different?<br>

<br /> <br /> Given the relatively limited power of the 430EX, it is useful for the flash to know when I am using the lens out at 105mm. Also, I have only had the flash for a few days, so it should still be possible to return it if this represents a defect.<br>

<br /> <br /> Many thanks for your help,<br>

<br /> Milan</p>

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<p>I have observed the following behaviour with the 430ex:<br>

When zooming from wide to tele, the flash will follow immediately. When zooming from tele to wide, the flash will follow immediately if you had used AF recently (in the last few seconds). If that was not the case, the flash stays where it was ... until you engage AF ... then it will set the correct focal length immediately again.<br>

One other thing: The flash will only adjust to focal length, if it is set to point forwards ... if you set it to point upwards by just one click, it will switch to a fixed setting.</p>


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<p>"The flash will only adjust to focal length, if it is set to point forwards ... if you set it to point upwards by just one click, it will switch to a fixed setting."<br>

<br /> That explains it.<br>

<br /> It is a bit odd, however. I thought the whole point of getting a flash like the 430EX was to be able to bounce it off things.</p>

<p>Thanks a lot for the information.</p>

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<p><em>"I suppose there is no way for the flash to know how high the ceiling is, and thus how much to adjust the spread of the beam so as to properly illuminate the subject in focus."</em></p>

<p>Correct, the flash does not do this but it doesn't need to. Think about it logically... when the flash fires at the ceiling, the light automatically bounces off the ceiling and onto the walls, floor and whatever else is in the room including the subject you are trying to photograph. It doesn't matter whether you're taking a picture inside a telephone box or in the Royal Albert Hall... the light will bounce around naturally and when your camera has detected that it has enough light to correctly expose the subject it tells the flashgun to stop pumping out light. If all goes well, the photo will be perfectly exposed. The only difficulty arises when the flash cannot pump out enough light to light the subject sufficiently... this usually occurs when the room is too large or the ceiling is the wrong colour and can't reflect the light enough (e.g. a black ceiling instead of white) or you're not using a high enough ISO or have the aperture set too small.</p>

<p>To keep things simple, put the camera in program mode, tilt the flash head towards the ceiling and let the camera do the work for you. If the result is too dark, increase the ISO.</p>

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<p>My thinking was that for a simple bounce off the ceiling, the focal length would still be useful information. The aim is to prevent light from being wasted on things outside the area being photographed. If the spread of a flash is sufficient when aimed straight forward, it should be more than sufficient once it has bounced off something and become effectively 'larger' (though less bright).</p>

<p>In any case, I am relieved to learn the flash is working as designed.</p>

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