>Is there not perhaps a difference in 'in-lens' vignetting opposed to >vignetting because of an external filter? My experience with putting a Cokin >filter holder on my 20-35/2.8 (before I cut the last two slots out) was that >vignetting definitely got worse as you stopped down. The Vignetting was not >visible through the lens at all while focusing (never tried DOF preview) and >all my slides had their corners badly blacked out. I had the same effect >once when I accidentally put the lens hood on without lining up the little >red dots.
If you think of vigneting as the relation between light that "should" reach the film, and light that "really" reaches the film, the vigneting will always decrease as you stop down. A different question is how "bad" is vigneting. It not only depeds on the vigneting amount, but on how is its distribution. Let's consider two cases of 1 stop vigneting (half the correct amount of light reaching the film). In the first case, vigneting is distributed all over the image. There is a 1 stop loss, but it can be compensated with an exposure increase. There is vigneting but you cannot see it. In the second case, vigneting is only in the outer region of the image circle. You get dark corners for half the area of the image (1 stop) and the rest of the image becomes unnafected. In that case no compensation can be made. In practice you don't get such extreme cases. As you stop down, the total vigenting decreases, but the outer regions of the image become also darker as the hood, filter, etc.. go in focus. That's why vigneting, in fact, decreses as you stop down and (sometimes, not always) image gets also worse stopping down. >Regards >Thys Best regards Vicente * **** ******* *********************************************************** * For list instructions, including unsubscribe, see: * http://www.a1.nl/phomepag/markerink/eos_list.htm ***********************************************************
