On Amazon, the Canon EF 70-200mm f/2.8L IS II USM Telephoto Zoom Lens for Canon SLR Cameras is $2500 whereas the Canon EF 70-200mm f/2.8L USM Telephoto Zoom Lens for Canon SLR Cameras is a mere $1400. Why is there such an important price difference? I'm saving to buy the cheaper one; should I wait, save more money and buy the "better" one?
Adding to to the answer above it has to be mentioned that a zoom lens benefits significantly from the Image stabilizer. I own the IS lens and can tell you that the effect is very strong, specially if you use a 1.4 or higher extension on the lens.
The price difference is given by the fact that the non-IS lens you listed here is much older (its the first, not the II model) AND lacks the image stabilizer. You should read reviews of all 4 lenses (IS vs. non-IS, I vs II) To see how big the quality difference is and if it matters to you. If you look for example at the lens flare comparison, the older lenses perform MUCH worse than the new ones, similar for contrast.
In general, I can only recommend to never save on a lens, specially the L lenses since they last for a very long time and are more important than having a good camera in my opinion. You will change bodies over the years more often than throwing out a lens and getting the successor model.
To start with
II are two different things. The
II indicate that this is the second-generation
IS means "image stabilizer", i.e. a system that reduces hand-shake. This system will allow you to take sharp pictures with a lot longer shutter speed. However, it doesn't do you any good if the subject moves...
If you need it? There is no way to tell.
An alternative would be a used
70-200/2.8 IS, i.e. the first generation. This is cheaper than the
II version, but most users would not notice any difference in image quality.
Also, if you think that the
ISfeature is more important than aperture, you could also consider the
70-200/4 IS. This lens is way lighter and smaller yet delivers great pictures.
"The one that isn't IS II" was introduced in 1995 when expectations for a high priced telephoto zoom lens were based on the performance of film and how images taken using film were generally used. Film is generally less demanding than digital:
- Since the film that just came off a tightly wound spool doesn't usually lay perfectly flat behind the shutter, the shape of the film can affect overall image sharpness more than slight differences in lens performance affect image sharpness. With digital, on the other hand, the sensor is almost perfectly flat and (should be) almost perfectly aligned with the camera's lens mounting flange. Very small variations between lenses are more noticeable with digital, particularly when we are pixel peeping images made with high resolution sensors. Many of those same variations would be indistinguishable when using film that isn't perfectly flat.
- The emulsion layers of color film meant that the distance from the lens was slightly different for each of the three wavelengths of light at which each layer was most sensitive. Different wavelengths of light are refracted at slightly different angles by the same lens and cause optical aberrations, most noticeably chromatic aberration (CA). Even if a lens was perfectly focused for one of the layers in the emulsion, it would be ever so slightly imperfectly focused for the other two layers. Digital sensors have color filters over photosites (a/k/a sensels, pixel wells, etc.) that are all the same distance from the lens. This has encouraged manufacturers to correct for chromatic aberration, as well as the other "classic" aberrations, more than they did in the film era.
- Very few images shot with 35mm film were ever enlarged beyond about 8x10 inches. Most were printed at 4x6 inches or smaller. When we "pixel peep" a 24MP image on a 23" HD (1920x1080) monitor, we are looking at an enlargement ratio that is the equivalent of a piece of a 60x40 inch print! Things not evident at an 8x10 inch display size will be very noticeable at six times the enlargement.
As digital imaging overtook film and became the overwhelming "de facto" medium used to record most photos, the market demanded better lenses than the best that were available in the film era. The advent of supercomputers has aided the design process of new lenses as computer models can test changes in design in a matter of hours what once took weeks or months to test via physical prototypes. The newer lenses are often much sharper than most of their film era counterparts.
Here's a side-by-side comparison of the 1995 Canon EF 70-200mm f/2.8 L to the 2010 Canon EF 70-200mm f/2.8 L IS II at DxO Mark. At 135mm and f/2.8, the difference is rather striking.
At 70mm and f/2.8, the difference is much less, but it remains fairly constant all the way from the center of the frame to the edge and corners.
At 200mm, the "IS II" has an even larger advantage over the 1995 non-IS lens, although at the corners the older lens gets very close to the 2010 "IS II".
The other big difference is IS (Image Stabilization). The 1995 EF 70-200mm f/2.8 L USM doesn't have it. The EF 70-200mm f/2.8 L IS II USM does. The now discontinued 2001 EF 70-200mm f/2.8 L IS USM also has IS, and you may be able to find a used copy of that lens for not much more than a new copy of the 1995 non-IS lens. The effectiveness of the IS used in the 2001 "IS" version is a bit less than the updated IS used in the 2010 "IS II".
Whether IS will be helpful, or even critically required for you depends on how you plan to use the lens. IS helps decrease the influence of camera movement when using longer shutter times (a/k/a "slower shutter speeds"). Is does nothing to reduce the influence of subject movement while the shutter is open. If you are shooting sports or action and using proper camera handling technique, you'll probably need to use shutter times short enough that there will be very little benefit from IS. If, on the other hand, you are shooting static scenes in very low light without a tripod, IS will be invaluable.
Beyond acuttance and IS, there are other considerations: flare resistance, geometric distortion, peripheral light falloff, etc. In general, lenses designed in the digital era have better lens coatings on more of the lens elements and are more resistant to flare. This was required due to the higher reflectivity of the front of digital sensors and the filter stacks directly in front of them when compared to the reflectivity of film. For the same lens class (i.e 70-200mm f/2.8 lenses), the newer ones tend to demonstrate less geometric distortion and light falloff in the corners, although improvements in these areas tend to be more marginal.