flash for macro

[stl]

is an external flash a must for macro photos? why is it i seen people taking macro with external flash? what's the reason leh?

[denizenx]

cos usually too close to lens, get blocked, and/or flash too powerful due to being too close causing exposure probs...
external MACRO flash surrounds the subject and hence can have balanced exposure, OR bounce an external flash for same reason, and solve the location prob too..

[stl]

Quote: Originally posted by denizenx cos usually too close to lens, get blocked, and/or flash too powerful due to being too close causing exposure probs... external MACRO flash surrounds the subject and hence can have balanced exposure, OR bounce an external flash for same reason, and solve the location prob too..

what if i dun use built-in flash? what does the bounce flash means?

Quote: Originally posted by stl is an external flash a must for macro photos? why is it i seen people taking macro with external flash? what's the reason leh?

The primary purpose of flash is to provide sufficient supplementary light to achieve proper exposure of one's scene. The main reason why macro photography tends to require flash lighting is that the shallow depth of field yielded by macro (and close-up) lenses often necessitates the use of small apertures, which in turn will require slower shutter speeds if no additional light were to be supplied. Since such shutter speeds are often too slow for freezing one's subject and/or handholding, it is generally preferred to employ flash in such situations.

Having said that, this is certainly not a hard and fast rule, so you shouldn't feel obligated to use external flash just because "lots of other people do it". Try it out yourself and learn the strengths and limitations of various approaches and techniques, and then decide for yourself. Like in so many other aspect of photography, one should choose one's tools to fit the task.

[jasonpgc]

If the flash is the main light source marco, use external flash with a matching shoe cord.

The reason why people uses external flash is due to the length of the marco lens. The built in flash is not high enough. When you move very close to your subject, part of the flash light will be blocked by the long lens. A shadow will appear on your picture. I call this "lens shadow".

I always use a shoe cord, hold the flash and the lens with my left hand. both pointing towards the subject. This will shorten the distance between the flash and subject, and also avoid lens shadow.

Another reason is due to the higher power (also known as Guide Number) from external flash. For marco, you would want all or most of your subject to stay within the DOF. However, by increasing the DOF you have to reduce the aperture size. Thus, you'll loss half the range of your flash with every stop of aperture reduced. The formula for getting the effective range for your flash is

At ISO 100

Effective Range=(Guide no)/(Aperture Size)

At ISO 200

Effective Range=(Guide no)/(Aperture Size)*2

and so on for ISO 400(*4), ISO 800(*8)....

For example,

With f22, using the built in flash(GN 12m at ISO 100), your effective range is only 12m/22 = 0.545 meters at ISO 100.

For an external flash with GN 42m, the effective range is 42m/22 = 1.91m at ISO 100.