Through my travels in the universe, a small practice, done mostly by scientists who work in the outdoors has really begun to bother me: using a DSLR lens cap as a photo scale.
I understand the appeal: I use to do it myself. You have a DSLR, the cap has to come off while you take the photo and you need a reference in your photo so you know how big everything is. It’s like a marriage made in heaven, except for one small problem: lens caps come in different sizes.
I’ve currently got in my kit lenses with 52mm, 55mm and 72mm lens caps…and the size markings don’t show up in photos easy (they are generally printed on the back of the cap). Lens cap sizes can range from around 30mm to over 100mm. They vary so much, and it’s not like there aren’t any alternatives.
Go buy a proper photo scale, go find a ruler in your desk drawer, carry a 50 cent coin (they have a unique shape that makes them easy to distinguish from other coins)…or be like me and have a photo scale built into your business cards: just skip lens caps; it will make life a bit easier when you or someone else is looking at your photo’s later.