Often do I hear my students admitting they never change the lens on their DSLR because of their fear to get dust in the camera. I do find this case rather absurd given that one of the benefits to use a DSLR is the ability to use the most suited lens for a given scene. One would be better off investing in a compact camera or use a mobile phone.
While the above video is more an humoristic rant, some simple steps will enable you to swap your lenses despite the rain, sand or dust.
It is obvious that if you are under the rain, your first try is to find some kind of shelter to change your lens. If you are in the outdoors then, a tree can be an alternative. If there are none then the old under the jacket method or from inside your camera or plastic bag will do. There is nothing difficult about changing a lens so you should be able to do it blindly. Since rain falls vertically or about 80 degrees due to the wind, it is a good practice to point your DSLR to the ground. Don’t be afraid to wet the outside of your camera body. Even if it is not weather resistant like the pro models, drizzling rain is harmless.
Sand or dust
Sand only moves with the wind so if there is no wind, you can swap your lenses without much care. If it is windy, you can follow the steps mentioned in the above video and point your camera away from the wind. unlike rain, fine sand and dust can float in the air in all directions. Pointing your DSLR towards the ground is not a smart choice since neither sand nor dust cares much for Newton’s gravity law. I suggest that in a windy condition you follow the same process as with rain using your jacket or a bag. Some camera bags do include an inner bag to protect your gear from the element, such as the Lowepro Flipside Sport 20L AW I reviewed a few years ago:
Please stop living in fear of dust, sand or rain. Despite following the above steps you are bound to get some dust on your sensor and in your lens at some stage. While in the lens it will most likely never be an issue, when you get some on your sensor, simply get it cleaned. I would recommend against doing it yourself. There are photography stores or show that offer cleaning service sometimes for free during special events. Keep your eyes open for those and shoot in peace with the most appropriate lens for the scene.