This is a sharp, compact and light weight, image-stabilized lens that packs a lot of performance into a relatively affordable package. There is a widespread view that the image stabilized (IS) version of the EF 300mm f/4 is not quite as sharp as the earlier non-IS view. This revision of my original view confirms that view.

Performance Data and Images When Used as a 300mm Lens

	I tested the EF 300mm f/4 L IS lens against my EF 300mm f/2.8 L (non-IS) lens and an EF 300mm f/4 L non-IS as described here. Center-weighted resolution (60% center, 30% middle; 10% edge) was excellent from f/4 to f/8. Drop off in resolution was noticeable in film from f/11 to f/22. The Non-IS f/4L lens has better resolution performance at f/5.6, 11 and 16 than the IS f/4L lens.
	I tested 50% modulation transfer function (MTF) using Koren 2003 lens test charts with an EOS-1Ds using in camera large jpg mode as described here. The non-IS version of the f/4L lens has better microcontrast than the IS version at all apertures tested.
Crop from Full Size Large Fine JPG File	Crop from Full Size Large Fine JPG File
Contrast and Detail at f/5.6 of high school band member in 2003 University of Florida Homecoming Parade. Subject detail, contrast and color is excellent, and background clutter along the parade route is still nicely blurred. Canon EOS-10D; EF 300mm f/4 L IS at f/5.6, ISO 400, 1/1600 sec.	Shot Wide Open: Local beauty queen in 2003 Univerity of Florida Homecoming Parade. Shooting at f/4 provides plenty of lovely detail while washing out the crowd and brick building in the background. Lower contrast is present in images at f/4. Canon EOS-10D; EF 300mm f/4 L IS at f/4, ISO 200, 1/500 sec.

Examples of Bokeh and Resolution Comparisons between the EF 300mm f/4 L IS and EF 300mm f/2.8 with EOS-1Ds and EOS-10D
Comparison photographs of mannequin here.

The film resolution tests show that the EF 300mm f/2.8 L lens has a slight resolution edge over the EF 300mm f/4 L IS lens at f/4. Does this higher resolution on film translate into a detectable difference in images produced with digital cameras? Tests with the EOS-1Ds showed that the slightly higher resolution of the f/2.8 lens is just barely detectable in digital photographs with this 11 megapixel camera. The difference in resolution is not detectable with the EOS-10D (6 megapixel camera).
Diffuse background blurring is slightly better with the EF 300 f/2.8 at f/4 than with the EF 300 f/4 at f/4 as shown in the full field EOS-1Ds images on the mannequin photo page.

For most photographic applications, differences in photographs produced by the EF 300mm f/4 L IS USM lens compared to those produced by the EF 300mm f/2.8 L lens are going to be photographically insignificant.

Performance Data and Images When Used as a 420mm Lens with an Extender EF 1.4x

	Putting a Canon Extender EF 1.4x on the EF 300mm f/4 L IS yields a reasonably well-performing 420mm lens. However, the performance window is narrow between f/8 and f/11. Performance is noticeably better than that for the EF 100-400mm f/4.5-5.6 L IS Zoom at 400mm. Performance pales against that of Canon's latest EF 400mm f/2.8 L IS lens.
Full Size Detail Cropped from Converted Raw File From Image Taken 1 Second Later to Reduce Canopy Reflection	Full Size Detail Cropped from Converted Raw File
Good aircraft and cockpit detail is captured when shooting at 420mm. Heritage flight of F-15 and P-51 at 2003 Wings and Waves Airshow, Daytona Beach, FL Canon EOS-10D; EF 300mm f/4 L IS with EF 1.4x @ f/8, ISO 400, 1/1250 sec.	Cockpit and aircraft port grill detail on F-15 in tactical demonstration flight. 2003 Wings and Waves Airshow, Daytona Beach, FL Canon EOS-10D; EF 300mm f/4 L IS with EF 1.4x (420mm) @ f/8, ISO 400, 1/800 sec.

Autofocus Function
Autofocus performance of the EF 300mm f/4 L IS lens is dependent on camera body. Autofocus is very fast with the EOS-1D / 1Ds. Autofocus is considerably slower with the EOS-10D or D-60. Autofocus with the 1.4x extender on the lens substantially decreases autofocus function. However, I was still able to track and photograph flying birds with an EOS-1Ds with the 1.4x extender on the lens. I was unable to directly compare autofocus function of the IS and non-IS versions of the lens.

Image Stabilization Image stabilization on this lens is a major benefit This photograph of a female anhinga was taken at 420mm with the camera hand held at a shutter speed of 1/50th second. The photographic rule of thumb is that you shouldn't try to handhold a telephoto lens for photography with the shutter speed slower than 1/focal length. The rule of thumb suggests that I shouldn't try to photograph this anhinga at less than 1/420 second. The image is moderately sharp despite the shutter speed being set 8-fold slower than the recommended shutter speed thanks to Canon's image stabilization system. Canon EOS-1Ds; EF 300mm f/4 L IS with EF 1.4x (420mm) @ f/8, ISO 400, 1/50 sec. hand held

Comparison of the IS and Non-IS versions of the f/4L:
I hesitated buying the IS version of the lens because of information at photodo.com cited by many on internet bulletin boards indicating that the newer IS version did not perform as well optically as did the older non-IS version of the lens. Photodo.com assesses the optical grade of the IS lens at 3.4 and the older non-IS version at 4.3.

Since posting my original review in November, 2003, Malcolm Stewart posted Canon MTF charts on dpreview.com that had been printed by Canon in 1999 showing that the new IS version of the lens had at least comparable, if not better, optical performance than the non-IS version.

My most recent tests confirm that the non-IS version has better resolution and 50% MTF function than the IS version. However, image stabilization is a benefit that may be worth the decrease in MTF performance for many.

Relevant Specifications for the EF 300mm f/4 L IS and EF 300mm f/2.8 IS Lenses from the B&H Photo Website and Canon-USA website as of November, 2003.

Concluding Opinion

The EF 300mm f/4 L IS USM lens is a very sharp, light, compact, high-performance telephoto lens. It is a valuable substitute for the EF 300mm f/2.8 L when weight, space (or cost) restrictions do not allow use of the larger and heavier, slightly more capable lens. Light weight and image stabilization make it a superb lens to use when you are traveling without a monopod or tripod.

Link to Bob Atkins' review of the EF 300mm f/4 L on Photo.net

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© 2003-4, William L. Castleman
Posted November 11, 2003. Revisions posted November 17, 2003 and new data added November 7, 2004