Which microscope objective should I start with?

Your microscope is set up and ready. Your specimens are tiny. Why wouldn’t you switch to the highest magnification objective straight off the bat?

While the highest magnification might seem best, most people find the opposite – in the end, it’s faster to start off at the lowest magnification.

This may sound counter-intuitive, but there are good reasons to start small.

Field of view

As you increase magnification, you’re able to see more less and less of your sample. Like holding a photograph up to your eye, you can only get a good look at a small section of the larger image.

Unless you strike it lucky and manage to zoom in on the exact part of the sample you want to observe, searching for your target at higher magnifications is going to turn into a chore. 

You’ll be scrolling around for far longer than it would have taken had you started at a lower magnification where you could see the whole sample.

Focusing time

At high magnifications, you’ll be using the fine focus controls. (The coarse focus controls will move the stage too much and you can easily ram the objective lens into your sample slide.)

But the fine focus controls are just that – they’re meant to be used for fine, precise adjustments to compensate for minor differences between objectives.

Using them to bring your target into focus from scratch will waste time, especially if your specimen happens to be way out of focus.

Working up is faster than you think

The standard procedure for microscopy work is to start with the 4x objective and work your way up through the objectives until you reach the magnification that you’re after.

While it sounds like more effort, it’s surprisingly easy thanks to parfocal lenses.

Most modern microscopes have parfocal objective lenses. What this means is that when one objective is in focus, all the other objectives are also in focus. (In practice, this isn’t always the case because of minor differences between the objectives, but it’s generally close enough that you only need to make very small adjustments to the focus.)

With parfocal lenses, it’s quick and easy to use lower magnifications to find your specimens, then simply switch to the higher objectives. You’ll find your specimens remain in focus and ready for inspection.

So, don’t be afraid to start at the bottom. You’ll be glad you did.