This lens is only marginally useful. While it is possible for a photographer who understands how to balance aperture and shutter speed to take a decent photo with this lens, doing so can be very difficult. Obviously, with the largest aperture of f/8, one understands that the subject must be brightly lit by sunlight. I expected this to be the case. I also expected to use this lens only with a tripod. However, the difficulty comes when one attempts to focus. Usually if I am photographing wildlife, I will focus with a live loupe view magnified 10x. The problem comes when touching the focus ring. The lens is so long that merely touching it jiggles the image enough so that focus becomes extremely difficult. In fact, when focusing, it is difficult to keep the subject in the field of view. This effect is doubled when the 2x extender is used. Add to this the extremely shallow depth of field that comes with a 500 mm lens, and one can see that getting an extremely sharp image with this lens is virtually impossible. It might be possible to avoid this issue if one were to set the camera on a table, or other stationary platform, that could be aimed at the subject. However, with an ordinary tripod, even a heavy one, focus is a challenge.Another issue relates to the orientation of the lens once it is screwed into the T-ring adapter. On my Canon 5D mark iii, when attached to the camera, the lens aperture control was located at the bottom of the lens. I found a little flat-blade screwdriver, such as one would use on eyeglasses, loosened the three set-screws, and was able to rotate the lens so that the aperture switch was at the top of the lens. While out in the field, however, I attached the 2x converter and found that when it was fully screwed on, the aperture lever was again near the bottom of the lens, in about the "8 o'clock" position. Luckily, I had taken the little screwdriver with me so that I could re-orient the lens so that the controls were visible on top.If the photographer understands the relationship between aperture and shutter speed, it is, in theory, possible to get an acceptable image at f/8 and a relatively slow shutter speed. However, this aperture issue, severely limits one's ability to photograph, say, a bird in a tree, if it is in the shade. Bright sunlight is essential, and the necessarily slower shutter speed makes it difficult to get an unblurred shot of a bird or a deer, unless it stands completely still for longer that about 1/30 of a second. The best I could do was in photographing these snapping turtles on a log, since they tend to move very slowly. Even so, I was required to bracket my focusing, by focusing just a hair past sharp, then backing up just the tiniest hair on focus, then repeating the process half a dozen times. Remember, however, that even touching the focus ring alters the field of view. The shallow depth of field at such high magnification is relieved somewhat by choosing a very small aperture. The trade-off here, though, is that f/16 or f/22 requires an even longer shutter speed. One must remember, too, that the physical length of this lens is sensitive to every puff of wind--so slow shutter speeds carry their own dangers.This lens may be of limited value for a young photographer as an educational tool. However, for one whose goal is really sharp, long-distance shots, a few more lens elements, a shorter lens, and a lot more money is required.