I want to model a locomotive, and hope to achieve a little specular effect using a normal map. You can see the very small bumps and indentations that make the loco bodyside bumpy and nonuniform. This would obviously be a huge waste to physically model, but would be interesting to see with a normal map.
How would I achieve these very slight dents without manually manipulating vertices? I hope there’s some modifier, but if not, it’s OK.
Some options.
Add a texture (cloud texture ?) to your material and use as a bump map.
Subdivide your object with multires modifier, use sculpt tools to make deformations. Make these deformations to a normal map and use with the original lower poly model
Subdivide the mesh with subsurf modifier and use a texture (cloud texture or other) with a displace modifier to create ‘real’ deformations instead of faked with normal map
Based on your reference image I would go with the bump map approach. Just plug a cloud texture into your Cycles material bump output. Play with the scale value and maybe add a color ramp for variation.
The bump approach is good for objects that will be viewed straight-on or at a distance. If you need to actually see geometry pop out from the side, or more close-up detail, then the Displace Modifier with a texture is the better approach to take.*
*Requires detailed geometry such as what you get after adding a SubDiv Modifier. So put your SubDiv before Displace in the stack.