Macro Lenses

Macro photography begins at the maximum magnification you have with a normal lens.  If you set your lens at its shortest distance (most lenses have a life size of 1:4) and look at your subject, the insect is still small in the view finder.  A macro lens is essential because it has an extra lens group to correct color and sharpness.  Macro lenses deliver a life size ratio of 1:1, meaning that a subject of 1 cm will project as 1 cm on the CCD sensor.  Many digital cameras have a magnification of 1.5 X, so this gives you a ratio of 1.5:1, which is useful for shooting insects.  

When I’m selecting a brand of lens, I always start with a 90 or 105 mm macro lens.   Sigma also has 150 and 180 mm, but these are difficult to use because even a small movement takes the insect out of the view of your camera.
 

Depth-of-Field: The zone, or range of distances, within a scene that will record as sharp.  

A Tamron 90 mm macro lens at the shortest distance to the subject (ratio 1:1) gives a depth-of-field of 1.6 mm with an aperture of F/5.6 and 4.6 mm at F/16.  You’ll need a high aperture setting of F/16 or higher to get sharp details of an insect, but you’ll also get a large shutter speed.  Most people would automatically say, “Oh, then you resolve it with high ISO of 400 or even 800.”  But high ISO creates drama in macro photography.  The noise will be large, the colors become unreal, and the image loses detail.  My advice: never use a higher ISO than 400; the lower, the better the quality your photos will be.  You can use a ninja noise plug-in in Photoshop to reduce the noise when shooting at 200 – 400 ISO.

You can download a free depth-of-field calculator at: www.dofmaster.com.

Exposure metering is a very important key in photography.  You need to understand how to use light.  The metering mode selection on a digital camera decides how the cameras exposure sensor will react when a photo is taken. 

There are three metering modes available.
1.  Center-Weighted Metering mode,

Center-weighted metering mode: this metering mode will not take care of badly exposed corners.  It’s more likely to address the average of the entire scene with an emphasis on the center area.  Also, the percent of the exposure calculation area grows to 75%.  This means that you’ll want to use it if your subject is centered (basically in portraiture) and no other parts of the background are essential to the message.  However, it’s probably the mode used least often.  Professional photographers choose it when Matrix Evaluation fails due to the complexity of the light in the proposed scene; it has the great advantage of no overexposed areas.

Matrix/multi-segment metering mode: the picture area is divided into different sections that are then metered with different cells.  For example: the light values from the center and the four other points in the frame are used to determine the exposure.  The center of the picture is given more “weight” than the other parts of the composition because the subject or the position in the frame that’s the most important is in the center.  Even in contrast lighting, this method produces correct exposures in many cases.

Spot metering mode: this metering mode can provide excellent results for high-contrast scenes.  It archives them by measuring the light in the center of the scene--about 1% to 3.5% of the image area--resulting in under/overexposed corners.  For example, when I’m shooting insects in backlighting, I use this mode to achieve the correct exposure.

Exposure meters, or light meters, are light sensing devices that are good at doing what the human eye can't--quantifying light.  With an exposure meter you can relate the brightness of light reflected from a subject toward the camera, or the brightness of the light illuminating the subject, to the sensitivity of the film.  The meter expresses this relationship in terms of lens openings and shutter speeds.

You can find more info concerning exposure meters at www.sekonic.com.