I have been doing a lot of backpacking recently, and the more I do, the more I feel the need to carry more focal lengths. One problem is that backpacking is never compatible with carrying more than a few lenses.
My usual combo comprises a Zuiko 28/f2.8 + Zuiko 50/f1.8 + Zuiko 100/f2.8 (with an Olympus OM-2N 35mm SLR); I am particularly fond of the 28mm right now. These make an extremely light combination since all of these lenses weigh around 200 grams each. Even though I am happy with this combination, I have always wanted to have an ultra-wide angle for landscapes and other dramatic effects (I am considering to buy a Zuiko 21/3.5).
Thus my main question is:
Is a 21mm + 28mm a useful and worthy combination for backpacking purposes?
I mean, these lenses are all very lightweight, and I am willing to carry them all if worthy; but so am I, so the slightest extra dead-weight will definitely slow me down, or make me suffer on the long run (especially for an upcoming 40-day backpacking trip that I am planning).
Also, the Zuiko 21/3.5 is not cheap, so I want to make a smart investment. I ask all of these questions because I have never used an ultra-wide angle and I know no-one around me who has (so actual testing and comparison is impossible).
Are 21mm + 28mm too close of focal-lengths to carry around together? Will I end up using only one of them on the long run? Or do they each serve their own particular purposes?
I am looking for experienced feedback and advice on the matter.