Keeping it clean
by Rod Barbee
As you may know, Iíve been using the Tokina 12-24mm wide angle zoom lens. So far, itís a great lens for me. There is just one really big thing to look out for when using these ultra-wide lenses, and thatís the crap that gets on the front element of the lens or on any filter youíre using. At a 15 mm focal length and an aperture of f/22, the hyperfocal point is around 2 feet. This means that if you focus there, everything from about 1 foot to infinity will be in focus. That one foot is measured from near the center of the lens. So really, anything thatís about 10 inches from the front of your lens to infinity will be in acceptably sharp focus.
At 12mm, things get even closer. By using hyperfocal focusing, everything from about 6 Ĺ inches from the front of your lens will be in focus. Thatís really cool when youíre photographing near-far landscapes. Whatís not so cool is that things even closer than this will also be sort of in focus. Maybe not sharp focus, but in focus enough for you to see. So if thereís anything at all on the front of your lens or filter, guess what? Itís going to show up in the final image. Just look at this picture from Bellevue City Park to see what I mean. Iíve been bitten by this more than I care to admit. Anyway, this means I need to keep an eye on the front of my lens and the blower bulb handy.
Here's another example.
This little fiber or hair or whatever landed on my polarizer. Now, I checked the depth of field (using my depth of field preview button) before starting this series of pictures, but I didn't check it before every picture, otherwise I would have seen this. This is just one more thing I need to remember to do when using this lens. It's not difficult to do, I just need to remember.
Solutions? Well, check the DOF preview button often. And keep an eye on the front element of the lens and any filters you add. Look out for scratched filters as well.
Sometimes, with these wide angle lenses, you don't really need to shoot at f/22. If you still need lots of depth of field but your foreground is five or six feet away (or farther), you can probably get away with f/8. Would this flying snake have shown up at f/8? I don't know, but it certainly would have been less visible.
This isn't the first time this has happened. Using this lens in Death Valley one morning, just a little bit of direct light hitting the polarizer caused some dust on the filter to be visible. This even when using the lens shade. The solution here, besides making sure everything is clean, is to look at the front of the lens to see if any direct light is hitting it. If it is, you'll need to stick a hat or hand or something out there to shade the lens. (workshop students make for very effective lens shades, by the way....)