This time I’d like to talk about a topic which is only indirectly related to microscopy: macro imaging. Taking high-quality macro images can be quite a challenge and can involve quite a bit of trial and error until one has found the ideal conditions. The pictures of the rose have been taken with a Sigma 70-300mm DG APO objective and a Canon EOS 450D camera. No artificial light was used, the exposure times were therefore quite long.
In order to obtain good looking macro images one has to take several measures:
- A solid, stable tripod: A heavy and stable tripod is absolutely necessary. Even the slightest vibrations (people walking, wind, shutter vibrations, etc.) will translate into a blurry image. I used a tripod designed for heavier video cameras.
- High f-stop values: Macro images generally have a low depth of field. In order to increase the depth of field it is necessary to increase the f-stop values. This again results in longer exposure times.
- Reducing shutter vibrations: Shutter vibrations can be minimized by using the mirror-lock up function of the camera. When the live-view feature of the camera is enabled, the mirror is in the “up” position. During release, the mirror does not have to swing up (because it is already up) and this significantly reduces vibrations. Not every SLR camera has a mirror lock-up feature, however. In this case, one can use a trick to completely eliminate shutter vibrations. Adjust the camera to have a long exposure time (let’s say 20 seconds). Cover the objective with a black cardboard, without touching the objective. Then release the shutter and wait 1 second for the system to stop vibrating. Then remove the black cardboard, this starts the exposure. One second before closing of the shutter cover the objective again. The opening and closing of the shutter (and mirror swing) will then take place while you have the black cardboard in front of the objective. Amateur astronomers use the same technique for taking vibration-free images of the night sky. They cover the telescope aperture with a dark cloth (without touching the telescope, of course).
- Long exposure times: This may come as a surprise for some. Long exposure times can result in more steady images because the duration of the vibrating camera/tripod system (after release) are much shorter than the total exposure time during which a steady image reaches the sensor of the camera.
Composition, artistic aspects etc.
- Sufficient ambient light: To prevent hard shadows, I decided to use the natural, indirect light of the room to take the picture of the rose. This results in longer exposure times, which makes a very stable tripod a necessity.
- Contrast: Make sure that the main object is set off from its background. This can be achieved either by blurring the background, or by making sure that the background has a distinctly different color.
- Exposure time: If you use a black background, then the camera may expose longer than necessary. The black background “fools” the camera into thinking that the image is too dark. This may result in the object being overexposed. Underexpose by 1-2 stops if the main object is too bright.
- Post processing: Crop the image and adjust the colors so that the background is completely black (if you use a black background). This will increase the impact of the picture.