Images are sharp and well saturated with color. The lens is bright through the viewfinder at 1:1, but as you increase magnification, the viewfinder image darkens noticeably. This is partially due to the simple fact that the front of the lens may shade the subject but it is also due to the bellows factor of the lens. The farther the distance the front element of the lens is from the film/sensor plane, the dimmer the light transmission. While your camera metering will compensate for this loss of light to obtain the proper exposure, there is no compensation through the viewfinder.
We field tested both outdoors and in a studio environment. After getting used to the handling of this lens, shooting from 3:1 or less is very doable in the field. Moving beyond 3:1 feels more appropriate for controlled environments such a studio shots -- though hardcore shooters will probably be willing to take it to 5:1 on location.
The magnification of this lens pulls you into your subjects, increasing and revealing the smallest of details. When you first start shooting images at life-size magnification you feel as if you've discovered a new world. The same can be said when you go beyond life-size! It may sound strange but once you get used to shooting at the higher magnifications, you'll begin to get frustrated because the view of your subject is blocked by a flower's anther (the individual filament of the pistil). The MP-E 65mm brings a hidden world to light, and the rewards pay off for the tough learning curve!
This lens definitely takes getting used to and it isn't for beginners. The sensitivity of the focus and depth of field of the MP-E 65mm can be frustrating for even seasoned macro photographers who are comfortable at 1:1 or even 2:1 with extension tubes. Once you learn macro photography with any of the quality 1:1 lenses on the market, work your way up to the MP-E 65mm (possibly experimenting with extension tubes/converters along the way). The greater working distances, less sensitive focus, and more forgiving depth of field makes such a lens easier to learn with. But once you get comfortable with life-size magnification the MP-E 65mm is an excellent way to expand your macro capabilities.
For the hardcore macro shooters, the Canon MP-E 65mm f2.8 1-5x Macro is one heck of a lens. It is a sharp, well built lens and it is matched by no other lens on the market. It is the only stand-alone consumer lens capable of going from life-size to five times life-size magnification. While there are other ways shoot beyond life-size magnification, it is tough to compete with the convenience and unbelievable magnification range of the MP-E 65mm. The MP-E 65mm is not a starter lens by any stretch but if you have experience with macro and are looking to expand your horizons, this lens comes highly recommended.