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This test tries to answer the following question:
When 300/4L is used with a tripod, should you turn the Image Stabilizer (IS) on or off?
According to the user manual, theoretically you should turn the IS off if the lens is on the tripod because the IS will cause blur when the sensor can not detect any motion. However, unless you have a perfect tripod and a perfect shutter trigger skill, there is always some motion even using a tripod. So, practically, should you turn the IS on or off when using 300/4L with a tripod?
To answer this question, I put my 300/4L and 350D on my Gitzo tripod and ball head. The iso is 1600. Camera is set to parameter 2. To simulate how the camera is used in the real world, I use my hand to trigger shutter (a).
The first row is taken with IS on and the second row is taken with IS off. The apertures from left to right are 4, 5.6, and 8, and the shutter speeds are 1/200, 1/100 and 1/50 respectively.
Here are the 100% center crops:
IS on
IS off
It is quite obvious, the image is sharper when the IS is on.
To further investigate this matter, now I use mirror lock up and the self-timer to trigger the shutter, reduce the iso from 1600 to 100, and auto level the pictures in photoshop cs2.
All pictures are taken at Aperture 4. The two on the top are without flash while the two on the bottom are with flash. The two on the left are IS on and the two on the right are IS off. The shutter speed is 1/6 without flash, 1/13 with flash.
Here are the 100% center crops.
Left (IS on), Right (IS off)
no flash
with flashAs you can see, this set of pictures is significantly sharper than the last set. This clearly shows how even a very small amount of vibration will significantly degrade the image quality of 300/4L. The pictures on the top shows that without flash, the pictures with IS on are still a tad sharper even with mirror lock up and self-timer shutter trigger.
Interestingly, the pictures on the bottom shows that with flash, the pictures with IS on are a little bit softer.
My conclusion is that theoretically you should turn the IS off if there is no vibration. However, practically, situations without any vibration are rare; hence you can turn the IS on all or most of the time even with tripod.
Note (a):I know there are many things you can do to minimize vibration when using a tripod such as mirror lock up or using self-timer to trigger the shutter. In the first test, I did none of them because when I am shooting moving birds, none of them could be applied. If you have a steadier hand or have more solid tripod, the result might be different.
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