But I have news!!!! I have a NEW LENS!!!! a telephoto! a NICE telephoto!
like my Sigma lens, this one is Prime (no adjustable zoom), 200mm f/2.8L. With the factor built into my camera that's like 320mm. Which is pretty good.
The f/2.8L part is what sold me on this particular lens (well, that and the fact that it was on a pretty significant sale). These numbers mean that the aperture is about twice as big as can be expected with this degree of telephoto (that's less than thousands of dollars, anyway) - all the other telephoto lenses I was looking at had apertures higher than 4, most at 5.6). The L part means it's canon's top-of-the-line.
SO: with this lens, my camera can take pictures of areas about as big as the top section of my thumb appears when my arm is stretched all the way out - better than with ANY other lens! Awesome, huh? Yeah it was a nice sale, but I'm still not telling how much it cost.
Here's an example of some sandhill cranes that would've looked like specks with my other lenses.
and
See the moon there? that gives a good idea of what 320mm means in terms of telephoto.
See that the moon is also out of focus? I was confused about this, because the cranes were really far away, so I thought that every picture taken that was focused for more than 300 meters away was easily focused for infinity as well. I was wrong.
After noticing this, I started reading up on lenses and focal planes and something called the "hyperfocal distance." Now I know so much more about why this happens. (and if you follow the link, so will you. But I explain it all below as well, so you don't need to.)
Basically it's because I was using such a big aperture... I was using the maximum aperture of 2.8 because I knew that with such a smaller area being photographed there is much less total light coming through the camera, so increasing the aperture would decrease the risk of me blurring the shot by holding the camera unsteady. That is true.
BUT WHAT I DIDN'T KNOW was that when the aperture goes up, the space in front and behind the focal plane (the distances away from you that are in focus, or "field") narrows considerably (for example, think about this picture taken with my sigma lens (very large aperture, smaller focal length):
Now, see how the nearest crust of the pizza is out of focus? Then a little bit farther out, the pizza is in focus. this is the start of my "field" in this picture. On this particular picture, just before the cut on the pizza is where the focal plane is, that is, where it is MOST in focus. Then it goes for another inch or so, and the field ends, and it is blurry from there on out. This lens had a aperture of 1.4 when I took this, and so the field was about 2 inches wide when focused that close (it would have been wider if everything was farther away). Had I made the aperture something smaller, say F/8 or something, the whole pizza would have been in focus, (but I would have had to use a tripod because of the limited light coming through, and I didn't have a tripod, so the whole thing would've been blurry. But that's beside the point.)
Now these "hyperfocal distances" are the nearest point to you that you can focus on AND have your horizon also in focus. You can look these up in a table for different lenses and apertures, but basically the higher the focal length and the bigger the aperture, the farther the hyperfocal distance. For my ultra-wide, the farthest hyper-focal distance is about 6 feet, which is why EVERYTHING - near and far - in all of those pictures always looks sharp. If I stop down the aperture (that's what it's called when you shrink the aperture size) I can get the hyperfocal distance as close as 1.5 feet. (I have yet to do that, but now want to try.) Here's an example of something like that with my ultra-wide. Note the depth of field, and the horizon:
SO, back to the telephoto - if I'm not focusing at or past my hyperfocal distance, anything at infinity (like the moon or the horizon) will be out of focus, just like it is for any other camera.
What is the hyperfocal distance for a 200mm lens at F/2.8 (the moon-picture setting), you may ask? 2343 feet. That's Really Far. It's definitely farther than those cranes were flying, which was my focal plane, so that's why infinity was blurry.
Here's a picture focused past the 2343ft mark (and cropped in just a bit):
Boring post? not to me!
Look, I'm learning!
Here's another nice picture taken with the telephoto (just because that's probably more of what you're interested in besides the theory):
and
but that last one got you thinking about depth of field again, right?
