F505V can not auto focus red object

There are two main types of autofocus sytems, active and passive. Active systems use a beam (usually IR) to calculate focus and the passive systems (which is what the F505 uses) use contrast differences. Both systems have weaknesses. The Active systems have limited range and can be fooled by shooting through glass which reflect the focus assist beams. Passive systems need good vertical lines to compare and they can be fooled by bright light behind the subject. In this case, you can see the sunlight just behind the flower and that probably attracted the attention of the AF system. One thing you can do to help in a difficult situation is to hold the camera at an angle (even 90 degrees) lock the focus and then return to the correct angle. In this case, a repositioning of the photographer to eliminate the backlighting would probably work as well.

Hello Ruchai - Do you mean specifically that it will not focus on these object specifically when in DIM light, or do you mean that it will not focus easily on red objects at all? This is important, because many of the flowers in people's gardens, including my wife's garden, are red. I shoot these all the time, and I have no trouble focusing at all. Now, if you are talking about dim light, it may be that the problem is the dimness of the light more than the color of the object. Pondria has done some interesting work studying that the camera's focus system may be 'seeing' everything as a b&w or grayscale tone in order for its autofocus system to work properly. I do not know if this the truth or not. But it the red color truly is a problem, perhaps there may be a workaround. Focus the camera upon a nearby portion of the plant -- the leaves, a stem, another flower of a different color, etc. Then half-press the shutter button. Finally, reframe the shot and fully depress the shutter button. I will try this today in my garden to see my results with red flowers and autofocus. I will attempt both the regular Autofocus as well as our lauded Spot-focus technique. :) Thanks for more interesting comments.