Does megapixel matter for black and white photography?
It all comes down to how big you want to print it. Good photo printing would be ~180 to 300 pixels an inch (the more ppi, the more quality). So if you have a 3.2 megapixel photo, you’re looking at a maximum print size of 8×10, with really high quality only going up to 5×6 or so. If you have a 6 megapixel, you could go up to 11×16 on decent quality, or ~8×10 on really high quality. For printing just 4x6s, I would recommend least 3 megapixels. Also: cropping. If you take a picture of a storefront from across the street, with a lower resolution camera you might not be able to make the text. With 6 megapixels, though, you could crop down to a fifth of the image and have a nice 640×480 close-up for putting on the web.
In PS, my preferred method is to go to the Channel Mixer, set it to Monochrome, and then tweak the different levels of red, green, and blue, making sure that the values of all three add up to 100%. I just wanted to repeat this, because it really is the best way to turn color into B&W. Mainly because it lets you replicate the effect of the color filters (particularly red) that are often used in traditional B&W photography.
