QUOTE(Seng_Kiat @ Mar 6 2009, 10:44 AM)
Ok. Nice explanation. I got it.

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here come the question.. which should I get? ..

.. my situation, I have A300 with single kit lens + sigma 70-300mm (with Macro at 200-300). So, the question is, to get better picture quality for macro purpose, which one 1 buy 1st, a flash gun or a macro lens? I know, get both is the best but my budget says big big NO for it.

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A few pages back, a lot of peoples talking about flash, cobra, etc. What actually cobra can do that others can't? Thank you all.

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If you're on a budget, then I would suggest you get the F42 flash and DIY an alien gun fix-on attachment for macro lighting. Just ask ryzan about the alien gun. The F42 can do wireless and you do not really need the strobe or the 'cobra' action of the F58 for macro.
Big question here is are you really into macro? If you are, then only consider getting a macro lens. For now use the Sigma to practice first.
If you are not on too tight a budget, then go for the F58 or cobra.
Why is it called a cobra? Because the F58 can move its head and neck to the left and right just like a snake lor... this is more for portraiture shoots. Imagine the F58 facing you directly. The F58 can move 90 degrees left or right until the flash head plus the neck is like lying on its side either to the left or right. Other flashes need to have separate bracket to do that.
Hard to explain lar using words. Don't have picture....