Comet Labs WN591 Bedienungsanleitung PDF herunterladen (Seite 16)

Help! There is a comet in my computer! 13

3.4.1 And I measured my comet at 400× magnification...

While we are talking about lengths, scaling factors and related topics, let us discuss a

common misconception about “magnification”. We recorded an image of a comet and now

we want to publish it. For publication, we need to quote the scaling of the image. Let us

say that we observed the comets under the microscope, using a 40× objective and 10×

eyepieces. We looked at the comets under a microscope at 400× magnification, because the

laws of optics state that the final magnification of the image observed equals the product of

the magnification of the objective and the magnification of the eyepiece (40 × 10 = 400).

Then we recorded an image. Can we now write in the caption of the printed (published)

image “at 400× magnification”? No, because this is wrong. In a microscope, the optical

path that leads from the objective to the eyepieces is different to that from the objective to

the camera (Figure 2C). There may be several lenses of different magnification inserted in

the objective-camera optical path. A camera is mounted on a microscope with an adapter,

and the magnification of commonly used adapters are 0.63× or 1×. Hence, to describe the

scaling of an image, we need to insert a scale bar (Figure 7).

The same principle applies to writing the Materials and Methods section of scientific

publications. We can mention the magnification of the objective that we used (40×), but

not write “Images were recorded at 400× magnification”.

Figure 7. Scaling of a printed image. Printed images should contain a scale bar. This image was

recorded using a 40× objective, at the scaling factor of the original image 0.36 µm per pixel. In an

image editing program (e.g. Adobe Photoshop), we can add a scale bar to the original image,

which is exactly 56 pixels long to represent 20 µm (20 µm / 0.36 µm pixel

-1

= 56 pixels). We then

save the image containing the scale bar. Now, we can enlarge or shrink the size of the image - the

scale bar always represents the exact current magnification. If printed on A4 paper, the size of the

scale bar for the image on the left is 16 mm and for the one on the right 6.5 mm. Hence, in the

printed version, the left image is shown (printed) at magnification 800× and the right one at 325×

(16mm / 20 µm = 800; 6.5 mm / 20 µm = 325).

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Comet Labs WN591 Bedienungsanleitung Seite 16