articles/Nature/extrememacro-page4

Extreme Macro - part 4 of 1 2 3 4 5 6 7

by Mike McNamee Published 01/10/2010

This procedure sounds difficult; is very difficult to write about, but is actually quite easy once you have done it a few times.

Setting Up

Test shots are fired off before the specimen is introduced to confirm the= exposure and particularly to check for any glare and reflections from the many glass interfaces that are kicking about. We usually find that 1/4 power is OK at 200ISO, f16 and around 1:1 magnification. You can fine tune the exposure (for the thickness of the insect for example) using the aperture, moving the guns nearer or further away or by going back to the flash guns and reducing the setting on the manual flash power. We rarely use TTL metering.

The lower powers also give faster recycling times for the flash. At 1/16 you may shoot at 6fps for 8 frames; at 1/128 for 40 frames. Very short flash durations are a boon in macro photography; conversely vibration is an ever-present problem. The mirror slap of an SLR is very detrimental but at magnifications greater than 5x, the focal plane shutter is also a problem. The modern SLR shutter with a fastest speed of 1/8000s is moving at just short of the speed of sound at the end of its travel.

Small wonder then that stopping it produces vibration. At higher magnifications only leaf shutters are used on microscopes and sometimes the only way to control vibration is to work in a darkened room with the shutter already open and then to expose by triggering the flash, or turning the lights on and off for the required duration. It is not an issue for the type of work described in this feature but even the building foundations of microscope rooms have to be isolated from the rest of the laboratory if another room contains moving machinery. However, for our purposes mirror lock-up, fast flash and an electronic cable release are about all that is needed, but don't move about during the exposure!

On the modern camera, using Live View has brought benefits. Live view is present on most of today's modern DSLRs (see list) and when activated the mirror is locked up and the image is focused on either the camera screen or with a satellite monitor connected to the camera. It is an excellent way to work although there is a certain delay in shutter activation.

Lenses

Sadly the macro lens as a species has seen a population decline for quite a few years. Both Nikon and Canon madespecific lenses for use on bellows. They were usually simple 6-element Gauss designs which performed optimally at higher magnifications but lacked any of today's sophistication such as automatic diaphragms and exposure through-the-lens assistance. Without digging too far down memory lane the Nikon PB-4 bellows unit cost £96 in 1978; a good quality PB-6 unit today may be purchased second hand for around £500!

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