The value for money is very good but it's still an additional tip. I mounted on the base 18-55 Canon, we must rise to 20 ~ 21 not to see vignetting (dark corners rounded). Warning to the objectives of the game in the axis of the moving parts, vignetting may appear off-center, so apparent to about 24mm (for the centering will leave a bigger one side vignetting).
If you buy this product, you are probably in APS-C and not full sized, remember the crop factor (1.5 for most SLR, 1.6 in canon). A 18mm (like my 18-55), you will have a 13mm: 18 (long. Mini focus) * 1.6 (crop factor) * 0.45 (tip bought) = 13mm (not an 8mm).