Instruction: First, identify the target attributes from the provided list. Then, scan the product title, description, feature, and brand to extract the values associated with each target attribute. Finally, create a list of dictionaries, each containing the extracted attribute, its corresponding value, and the source where it was found.

Input:
Product title: Leica 011-081 Summicron-T 23/f2 ASPH Lens
Product description: Format favored by Leica photojournalist
Product feature: Equivalent to 35mm in 35mm format, Compact in size, Maximum aperture of f/2
Product price: $76.30
Product brand: Leica
Target attributes: Zoom Focal Length
Answer: attribute: zoom focal length
value: None
source: None