The Optical Marsupial
Anyone who owns two lenses and one camera has a problem - at some stage of the game they are going to have to change whatever is on the camera for whatever they are carrying in their camera bag. If they do not have a camera bag they have two problems, and if they are trying to do it in a hurry on in the twilight in the deepest part of the bush surrounded by tiger snakes...well they have more than two problems.
Here are a few suggestions to ease the situation:
1. Do not go into the bush at twilight in snake season, or if you do, ask for someone to drop a daisy-cutter bomb about 5 minutes before you enter the area.
2. Get yourself a lens-changing pouch. This will save you from dropping one or both of your lenses into the dirt.
The two smaller pouches seen in this post are made by Think Tank and Lowepro. They are both equipped with a belt loop to fix them to your off-side. The Lowepro has an additional shoulder strap.
The Lowepro is a traditional flap-top design with thick padding inside. There is a secure zipper around the edge of the lid - it is fairly water-resistant.
The Think Tank design has a purse-top that closes with a draw string. There is a separate compartment under the pouch with a waterproof cover.
The idea of these is that you can carry your spare lens in it for your venture, but as you are gently juggling the camera and optics out there in the field, you have somewhere to literally drop the one you are changing while you attach the new one. Wise photographers will keep some sort of a strap on their camera to sling it round a neck or shoulder while they do this.
The same sort of idea appends to the Lowepro Passport Sling II bag - you can sling it over a shouldeer then rotate it forward around your waist to give the effect of a secure kangaroo pouch in the front. Open it, extract the new lens, drop the old one in there - all safe and sound and not too much of a war-dance to do it.
Remember - make it easy on yourself and take it easy when you shoot. No-one benefits from over-complexity - ever.