Since publishing the first article on "stacked teleconverters" I have been contacted by many photographers who have claimed that I would receive images that were just as good as, or better, than using "stacked" teleconverters if I were to simply crop more tightly my images made with a single teleconverter. I recently had the opportunity to test this claim...

This is a full frame image I made of a Belted Kingfisher with a Canon EOS 1D MkII dslr, Canon EF 500mm f 4L IS lens, plus a Canon EF 2x II teleconverter.		This image of the Belted Kingfisher was made from the same position as the image to the left but, in addition to the 2x teleconverter, I added a Canon EF 1.4x II teleconverter.
The images, above, and posted later in this article were made at the same exposure settings: ISO 800, 1/1250 sec @ f 11. The camera and lens were mounted on a tripod with a gimbel head (Wimberley SideKick) and Image Stabilization was turned on. Both of these images were given the same contrast and tone corrections during the RAW file conversion to .tif image files. No other manipulations have been done other than to reduce the file size and save as .jpeg files for WWW presentation.

The Belted Kingfisher is one of my "nemesis" birds. It is very difficult to approach closely enough to make an effective image. I just happened across this kingfisher on one of my trips to the Gilbert Water Ranch in Gilbert, Arizona, USA. The kingfisher was quite uncharacteristically perched in plain view. I quickly made the first exposure with a 2x teleconverter attached to my 500mm lens. I wasn't too happy about how small the bird was in the image so I "stacked" the 1.4x tc to the 500mm lens + 2x tc and made the second exposure. Using the 500mm lens with the 2x teleconverter alone on my Canon 1D MkII dSLR yields an effective focal length of 1300mm. Combine this with the 1.4x teleconverter and the effective focal length becomes 1820mm. Below are comparison images made by cropping the same area in each image and keeping the kingfisher the same size in each image...

This is the kingfisher cropped from the image made with only the 2x teleconverter attached to the 500mm lens. There has been no sharpening performed on this image. At ISO 800 the crop is very noisy. Using an f stop of f 11 represents an aperture stopped down 1 f stop from wide open.

This crop from the image made with the 2x teleconverter and the 1.4x teleconverter "stacked" shows less noise and sharper details. Shadow details are just a little less than the image above but this would certainly be a useable image. Using an f stop of f 11 represents using the lens wide open at maximum aperture!

Judging by the appearance of the images, above, I would have to say that "stacking" teleconverters yields a much sharper image with contrast that is still acceptable as compared to cropping a small area from an image made with a single teleconverter. I, also, think this test speaks volumes about the following points...

• IMHO, this test speaks volumes about just how well corrected are the Canon "supertelephoto" lenses and the Canon teleconverters. Besides how well the sharpness and contrast holds up when using "stacked" teleconverters to make an image there is practically no chromatic aberrations in the images. There is just a minor amount of CA at the very corner of the "stacked" teleconverter image. This is remarkable. Also, consider that f 11 represents stopping down the 500mm lens 1 f stop when using the 2x teleconverter alone on the 500mm lens. On the other hand, f 11 represents setting the 500mm lens wide open when both the 2x and 1.4x teleconverters are stacked on the lens! WOW!
• IMHO, this test speaks volumes about the effectiveness of Canon's Image Stabilization as applied to the "supertelephoto" lenses. If you follow the old "rule" of using a shutter speed of 1/focal length of the lens, these images should have been made with shutter speeds of 1/1500 sec to 1/2000 sec. Image Stabilization allowed me to use shutter speeds nearly half of what the "rule" calls for. I have nerve damage due to diabetes and have a slight tremor all the time. Image Stabilization has been a godsend for me and has made ultra-long telephoto photography possible for me.
• IMHO, this test speaks volumes as to the accuracy of the autofocus system employed in the Canon 1D MkII dSLR. Both of these images were made using autofocus! The 1D MkII is not supposed to autofocus accurately with a maximum f stop of smaller than f 8. The maximum aperture of the 500mm lens + 2x tc + 1.4x tc is f 11. As long as there is good light and good contrast, the Canon EOS 1D MkII will autofocus accurately at f 11.
• IMHO, this test speaks volumes about just how good is my "long lens" photography technique! (OK, I'm just joking, here, but my long lens technique is pretty good! :) )

Given how well the test image using "stacked" teleconverters appears, I will not hesitate to use this technique more often when I have good, contrasty lighting conditions.

* Although this article is geared to Canon "Big Lens" photographers, I beleive that this technique may be used by Nikon photographers, too. It is my understanding, however, that one of the teleconverters may need to be modified so that it may be stacked with other teleconverters. I'm sure this information may be found on the Internet when visiting many of the Nikon user groups.