BetterPhoto Q&A
Category: Problems with Photo Equipment - Tips & Tricks

Photography Question 

Francine Elenga
 

Auto focus makles lens focus and then return to or


I love my camera but recently I have been having problems with the auto focus. When I try to take a natural light photo the lens focuses and then returns to the original position and will not take the photo. It will continually try to focus back and forth but will not do so. I have found this is true of distance photos and close up photos alike. I thought maybe it was the battery but I changed that and it didn't make any difference. HELP!!!!


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July 12, 2004

 

Jon Close
  Autofocus is not perfect and needs a minimum level of light to function. In dim light or with a subject that does not have good contrast it will not work reliably. Many accessory flashes have a red autofocus assist light that will project a pattern that the lens/camera can focus on in low/no light, or the camera's built-in flash will flicker to provide light for focusing. Depending on what make/model camera you have you may be able to set it so that the camera can activate the AF assist light without firing the flash.

The camera will also hunt and not find or lock focus if the maximum aperture of the lens is too small. Many autofocus SLRs need a lens with maximum aperture of f/5.6 or larger (smaller f-number) to function reliably. For example, if you are using a 28-300 f/3.5-6.3 or 100-300 f/4-6.7 zoom, the maximum aperture in the 200 to 300 zoom range is f/6.3 or f/6.7 which is too small AF is going to be iffy at those settings in any but the brightest light.


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July 13, 2004

 

Francine Elenga
  Thank you, Jon. I have been trying everything I know to remedy this problem. It happens in bright sunlight. I was up in the mountains taking photos of the landscape with a lake in the foreground. Also tried to take close-ups of some wildflowers with the macro but to no avail. Thanks again. Maybe I need to just use the manual focus in these situations.


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July 13, 2004

 
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