I am using full flash, fill flash and natural light for my macro work. and how I differentiate and decide which one to use (some how this related how I get my BG as discuss in
http://liewwk-macro.blogspot.com/2009/02/macro-pp2-how-i-control-background.html...ok let discuss
always follow rules below
1. Natural Light is my 1st priority
- if environment light is good
- environment allow me to use monopod (for 1" - 1/30) and tripod (>1")
- wind (this is main killer for my NL)... I will discuss how I over come this in future post
- bug is not move or move slow
Why ?
- NL will bring more BG color compare to other
- will not scare the bugs away
sample of fill flash
i. sample one to compare

ii. this is how I get the clean BG
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2. Fill Flash
- what this mean using manual flash (small normally I refer to 1/32-1/128) to fill in the minor under exp
- if environment light is good
- environment allow me to use monopod (for 1" - 1/30) and tripod (>1")
- wind (this is main killer for my NL)... I will discuss how I over come this in future post
- bug is not move or move slow
(same as above and why I need fill ?) - there are occasion, I still use flash but all above requirements meet where I should use NL instead .. why ?
i. shadow ..a sample I got for this
- a sample of shadow I refer
with fill flash

NL
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ii. some bug (dark color)tend to have too much shadow while shooting NL so I will fill the light onto it's body to resolve the shadow concern
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this dark blue beetle is a good sample but too bad I failed to capture it without flash
iii. fill flash object tend to be more saturate in color. this is not really my good reason as I can easily add saturation @RAW-->Jpeg
a same sample across 3 methods I discuss
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3. Full flash, some time I mean using TTL , eTTL ... and this don't matter what FEC [flash exposure compensation](hmmm this is CANON term and not really sure what other call ... ) ... as long as we let the body decide what do use mean it is call Full for me ...
- this is good to freeze the moment where include wind, handshake, bug move ...
- need small aperture for more DOF so slower Shutter speed
- tend to more sharp ? (not really but then as more DOF and avoid those movement so picture definite look sharper)
- lost BG , just like below

anything else ? may be I missed out something you want to know .. always drop me a message so I will reply you