7/6/99
Can anyone give me their formula or direct me to a reference on how to
accurately calculate the size of scale bar on photomicrographs?
Thanks,
Ruth
Ruth Yamawaki <yamawaki@leland.Stanford.EDU>
1. Think of a value for your scale bar, e.g. 1 micron (this should
always be a round figure, or reasonable fractions thereof),
2. Multiply this by the final print magnification of the micrograph,
3. This value is the length of the scale bar, in this case in microns.
Example:
If final print magnification is 22 300x,
and if you choose to have the scale bar representing 1 micron,
then scale bar length = 1 micron x 22 300 = 22 300 microns.
Then, as there are 1000 microns in a mm, the scale bar length on
the micrograph will have to be 22.3mm.
Clearly, depending on the magnification, sometimes you may
choose an impractical figure for the scale bar to represent.
If, for example you choose 1 micron for a magnification of 400x
then the scale bar would only be 400 microns (0.4mm) long. This is
crazy so how about choosing 20 microns? The scale bar would
then have to be 20 microns x 400 = 8000 microns = 8mm.
At the other end of the scale, if you have a magnification of
120 000x then a 1 micron scale bar would be 120mm - much too
long - so how about a 0.1 micron (or 100 nm) scale bar? Yes,
much better because then the scale bar would be 0.1 micron x
120 000 = 12 000 microns = 12mm.
PLEASE do not fall into the trap of doing it the other way around
and calculating what a bar of given length will represent. This
leaves you then with all your bars the same length (very neat, yes)
but representing crazy figures like 0.23 micron, 66 nm, etc!
Thanks for asking about this. Now, having written out the answer,
with examples, on the many occasions when I am asked the same
question by our users, I can simply pass on copies of this
message rather than do the explanation over and over again on the
board!
Good luck
Robin
Robin H Cross
Director : EM Unit, Rhodes University, Grahamstown, South Africa
R.Cross@ru.ac.za (or eurc@giraffe.ru.ac.za)
tel: +27 46 603 8168 - fax: +27 46 622 4377
http://www.ru.ac.za/emu/index.htm
I have found it quite useful to print out an Excel spreadsheet table with
values on it. One axis can have magnifications in 1,000s (eg
1,2,3,4,5,6,7,8,9,10,20,30,40,50,60,70,80,90,100,200,300,400,500) and the
other axis can have fixed values to be represented (eg
10,20,50,100,500nm;1,2,5,10,20um). The table can then contain the values in
mms.
It's almost foolproof and easy to run off copies for students, especially
when they realise that you can add bits together on the magnification side
to give you a scale bar length for say 13k = 10k + 3k so just add the two
entries in the table to get the length for a 2um bar. I imported this into a
word document because I wanted to shade bits of the table to give
recommended lengths for scale bars but it works fine.
I may have the Word 6.0 for Windows PC document somewhere. If you want a
copy post an e-mail to me (see e-mail address at bottom)
Malcolm
Malcolm Haswell
Electron Microscopy
School of Sciences
Fleming Building
University of Sunderland
SUNDERLAND SR1 3SD
Tyne and Wear
UK
Tel (0191) 515 2872
e-mail: malcolm.haswell@sunderland.ac.uk