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Canon 100-400 IS vs. Canon 400 f/5.6

April 8, 2010

I realize that at the time of this writing, these are fairly old designs and these lenses have been around for a while. However, this question does seem to pop up fairly often in online photography forums, hence this review. In addition, I was a little curious myself to see what the image quality differences between these two lenses are like. I have been very impressed with the IQ of my copy of the 100-400 and wanted to see how much better (if at all) the 400 prime could be.

Physical Size and Build



The 100-400 is a little fatter and when extended out to 400mm is just a little longer than the prime. Unsurprisingly, it ends up being much shorter than the prime when collapsed. The zoom is just a smidge heavier than prime as well.

Both are well built, but the prime has a more solid feel in my hands which shouldn't be too surprising given the push-pull design of the zoom.

Sharpness and Contrast

The first question most people ask is which is sharper. So lets get to it, but first, you can view/download the full size JPEGs here. Here is an image of the overall frame (zoom on left, prime on right):


First, notice how that even though the zoom was pulled all the way out to 400 (yes I triple checked this), the field of view is slightly wider than the prime. This is common among zoom lenses (they usually have a wider field of view at the long end and slightly narrower on the short end), its usually a limitation of the design. So if getting the absolute most reach is important to you, thats a plus in the prime's column.

These comparison images were all processed in Lightroom 3 with the noise reduction and sharpening set to the default values. Now lets get to center performance:


The zoom has impressive center sharpness, one could argue the prime is sharper, but I'm not sure there would be any real world difference. Notice that the zoom actually gets slightly less sharp when stopped down to f/8. Again, I had to take a couple of shots to verify I hadn't screwed something up and all were the same. Now lets take a look at corner crops:


The prime has a distinctive advantage here. In addition to having less vignetting, the prime is a little sharper both wide open and stopped down.

Bokeh

To test the bokeh I put a small light in the frame at a distance and then set both lenses by manual focus to the same distance (around 11 ft.) rendering the highlight out of focus.
Both look very similar, but to my eye the prime looks just a smidge smoother.

Autofocus

Without a doubt, the prime is better. The focus speed is really fast, as fast as Canon's top of the line super telephotos. The zoom, though not as fast is still quite respectable and is probably among the fastest of zooms with its range and aperture sizes.



The speed and responsiveness of the autofocus makes the 400 f/5.6 a great tool for photographing birds in flight.

Image Stabilizer

One of the distinctive advantages of the 100-400 is Image Stabilizer. Even though its an early generation of the technology and is only effective to 2 stops, it makes a huge difference when photographinga relatively static subject without a tripod.



Conclusion

I think one can use a very simple algorithm to pick between these two lenses. If you need the flexibility of a zoom and/or image stabilization the 100-400 is the clear choice. The image quality advantage at the edges of the frame when shooting wide open enjoyed by the prime in my opinion don't outweigh the flexiblity of the zoom and image stabilization (again assuming you need those things). However, if your intent is to mostly shoot fast moving subjects (especially birds in flight), then I think the 400 f/5.6 prime is a better choice. The faster auto-focus will help get better images and image stabilization won't be of much use (except maybe for panning blurs). Also, if reach is important to you, note that the zoom doesn't quite get you the field of view of a 400mm lens when set to 400. The Canon 7D + 400 f/5.6 represents at the time of this writing a moderately economical way to get superb flight shots.

I should also mention that the 400 f/5.6 prime would be the lens of choice for landscapes. I didn't focus on landscapes (and yes a telephoto can produce some very interesting landscapes) but its great sharpness and contrast right into the edges of a full frame image would make it a great landscape lens.


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