Reading a thread about someone struggling with graduated neutral density filters I thought I would post up a simple technique I have been using since film days with some success.
First of all I will point out that this is only practical for long, multi second, exposures on a tripod. As most of my work is landscape and I usually carry strong neutral density filters it suits my needs very well.
In simple terms the technique is to use something dark to block the light from part of the image for part of the exposure. The advantage of this over graduated ND filters is that the transition does not have to be a straight edge and can accommodate curved or even projecting horizons.
With my background in printing in the darkroom it came naturally to me to use my hand so I use a black glove, but I have more recently seen the method described as the "magic cloth" technique.
First of all I make a couple of exposures to determine the exposure required in different parts of the image. (I used to use a spot meter in my film days.) Let's say for example that the foreground needs 8 seconds but the sky only needs 2 seconds.
I start the 8 second exposure with my hand, in glove, close to the lens, obscuring the sky area and then smoothly withdraw my hand for the last two seconds. To find the right position I used to use the viewfinder which was a bit hit and miss but with my latest camera I use the Live View feature which is much more convenient.
The longer the exposure the more flexible the technique of course. Sometimes I find myself dodging different parts of the frame in complex lighting conditions.
This is not as flexible as HDR or exposure blending methods of course but it does sometimes allow you to get an image in one frame without complicated post processing.
Don't delete your original test exposures because if it doesn't work out you still have the exposures you need for a manual blend in the computer.
I don't know how useful you will find this info. It will depend on you style of photography I suppose but I thought it might be an interesting method to share.