[Taxacom] Digital herbarium

Sean Edwards sean.r.edwards at btinternet.com
Mon Feb 22 07:29:59 CST 2010

Yes, thanks Fabian, I agree.

But possibly some more useful points and responses though.

1. Yes you are right, I should have mentioned diffusing the light sources. At Manchester when I left we used 'white bank', that very thin paper that herbariums use for folders, it comes in very large sheets, double the size of herbarium sheets of course, and the set-up was jury-rigged into a very large hardboard box. Our lights then were special white balanced units. But white balance is so easy to deal with now as you say, almost whatever your light source is.

2. You are right about the lack of  'problems' using DSLRs, I guess that the fact I listed four of them made them seem more important than they are. So forgive me for giving two of them more space here:
a. You will find some lateral chromatic aberration (colour fringing at the edges) in macrolenses, agreed hardly significant, but is so easy to correct that you might as well build it into your workflow whatever your equipment. 
c. Dust. Well, if you always leave the lens on, why not use a fixed-lens digital camera, as we did (do?) at Manchester. Cheaper, and the results were excellent even then, six years ago. We did a series of tests to find the focal length that gave neither pincushion nor barrel distortion. No need to tie up an expensive DSLR. Some of the DSLR problems are now admitted to come 'endogenously', from spray from the mirror and other lubricated internal parts, but you will only notice this in photomicrography or very small-aperture extreme macrophotography: little 50 micron droplets that are quite visible when enlarged. I can personally vouch for this, and the only solution is a 'wet' clean. But I don't think you will need very small apertures for most herbarium sheet work (maybe only for the most bulky of specimens?), and even with full-frame f/8-11(-16) should be more than enough. Smaller apertures will take the edge off sharpness (diffraction), not much but why lose any detail? Do a test series.

I think these points need to be made, but in summary, as Fabian said: "I would consider advantages in handling and speed of [digital cameras] getting an image as far superior to scanners...."



Sean Edwards, email: sean.r.edwards at btinternet.com

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