Scale Bars - for Ken

[gpmatthews]

Following Ken's recent comments on scale bars, here is a summary of how I use them.

I keep a library of images of a stage micrometer (a microscope slide with rulings of known pitch, like a mini ruler) for combinations of ocular and objective for each of my microscopes, taken under fixed camera conditions of resolution and optical zoom (I only ever use digital zoom for focussing purposes).

Using an image editor I create a second transparent layer in each library image of the stage micrometer and create a scale bar in this layer. The image is then saved in an image format that preserves the layers. I can then copy the scale bar from the relevant layer, without the micrometer rulings, and paste it into any picture taken under the same conditions of ocular, objective, camera and camera zoom.

Here is an example from my library. Original image size is 2592 x 1944 pixels.


Microscope: Zeiss Standard GFL
Ocular: Olympus P15
Objective: Leitz x40 NPL Fluotar ICT
Camera: Canon Powershot S50
Zoom: Setting 5 (Focal length 14.7 mm)
Stage micrometer: 0.1 & 0.01 mm rulings (100 microns and 10 microns)

[rjlittlefield]

Graham,

A very clear description & illustration -- thanks for posting!

Ken, using the stage micrometer, I measure the field diameter in this image as 241 microns. Jahn's procedure would estimate 267 microns, assuming that "Olympus P15" means a 15X ocular giving 600X total. When I first looked at the description, I casually assumed that the ocular would be 10X, from which Jahn's procedure would give 400 microns. So even a careful estimate would be 10% off, and my mistaken assumption would make it 65% off. Scale bars to the rescue!

--Rik