Hi, I've been offline for some time, now I am back at TN to share my photos and to learn from others.
I've been calibrated some of my lenses recently to know magnification scale of my photos. The key is to know distance from matrix/film surface to photographed subject, you can measure and write it down while taking photos. But I have discovered recently that my DSLR with Canon lens attached writes focusing distance to subject in EXIF metadata (unfortunately only with system lenses...)! If I know that value and have my lens 'calibrated' (a series of measure photos done) I can calculate magnification scale of photo for given lens model (amount of pixels/mm) and there is no need to measure and write down distance to photographed subject. So, less work to do 'in the field', quite better.
Of course, this is less complicated (less to measure while calibrating) with prime lens, but I've calibrated also two of my zoom lens at their max focal length with good accuracy.
Here is a little demonstration - a photo with scale ruler on its edges. This is important for documental photography. The plant is Common AgrimonyAgrimonia eupatoria (Rosaceae) -- fruiting stem.
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Présentation pour le moins originale mais le sujet apprait suffisament détaillé pour que l'on apprécie la finesse des détails et la délicatesse des couleurs.
A bientôt sur TN pour de nouvelles aventures.