Trying to figure out the magnification of micrographs with no bar marker is a major pain in the neck. Trying to compensate, adjust, decipher and trust bar markers when they are actually present is hard enough, but when the don’t exist at all (typical get-around is the phrase “original magnification 177,000 or something like that which is absolutely useless in terms of measurements) it is even more difficult. Case in point, trying to figure out the size of the SP-D molecules, and those coshadowed with collagen, in a paper by Crouch et al. JBC, 1994.

To see whether i could find rotary shadowed type I collagen to compare their micrographs with i did find one image with a bar marker (who knows if that is accurate?) and found the collagen to have a diameter of about 5.4nm. This is pretty close to the limits of measuring anything with traditional TEM especially when the grains of the shadow material are almost that large. But regardless, I am going to use 5.2 as a collagen (and collagen like domain) measure to see if the images of rotary shadowed SP-D from Crouch et al will be similar to other preparations. (the leads to the comment — for whom are the publications really made…. for knowledge and as a resource, or just for building CVs of great length).

If the 5.2nm (or close… 5.3 or 5.4nm ) width for collagen type I measurement is applied to figure 3 of Crouch et al JBC, 1994, then a measured SP-D dodecamer (picked because it was clear and easy to draw a circle around that touched three CRDs) the molecule came out at about 136 nm which was better than i had hoped.