NASA’s Spirit Rover is providing a lesson to aspiring digital photographers: Spend your money on the lens, not the pixels. Anyone who has ever agonized over whether to buy a 3-megapixel or 4-megapixel digital camera might be surprised to learn that Spirit’s stunningly detailed images of Mars are made with a 1-megapixel model, a palm-sized 9-ounce marvel that would be coveted in any geek’s shirt pocket. Spirit’s images are IMAX quality, mission managers say.