why buy one if you can print one?

for anyone who still doesn´t know this comes very handy:

Free Lens Hoods

Printable PDF documents to make your own lens hoods

This site contains PDF documents that can be printed and cut out to make lens hoods for a variety of 35mm and digital SLR camera lenses. Lens hoods give better quality photographs by reducing flare caused by nonimageforming light.

www.lenshoods.co.uk

on and offline version of a very nice calculator

Depth of field scales are elegant tools for quickly and easily calculating depth of field and hyperfocal distance. Unfortunately, lens manufacturers don't engrave scales on lenses anymore. Now you can use DOFMaster to make your own scales.

Use DOFMaster to make depth of field scales for use in the field. Just set the focus distance, and read the near and far focus distances. Easily calculate the hyperfocal distance for your lens at any aperture.

www.dofmaster.com/dofjs.html

The Photographer's Screwdriver

The Photographer’s Screwdriver is a tool to calculate the depth of field (dof), hyperfocal distance, angle of view (aov) and the number of frames required for creating panoramic images. The Photographer’s Screwdriver is a Java program designed to run on mobile phones. It is available to be downloaded for free.

www.curved-light.net/software