It sounds like a bad idea. What if the shadow areas are dark rock? Or green foiliage when you are using a red filter? Both have substantially lower reflectivity than your palm (I'm assuming you are caucasian since you are from Sweden). The problem is that to get good shadow detail you don't need to know how much light is hitting your subject - which is what metering your palm will roughly tell you - but how much light is being reflected from your subject, which depends both on the incident light and on the reflectivity of the subject.
I'm also not sure what you mean be metering your palm if you have only an incident meter? An incident meter records the amount of light falling on the subject, not the amount of light reflecting off something (like your palm). For that you would need a reflective type meter. But if you have this then why not just meter the shadow area directly, and then adjust to place it in zone III or wherever you want it depending on the contrast range of the scene?
Last edited by andrew.roos; 04-08-2012 at 04:08 PM. Click to view previous post history.