I recently purchased the famous Canon 70-200mm f/2.8 IS USM lens for my Canon 40D. With it, I purchased the Canon 1.4x teleconverter. I read a lot of conjecture about how much resolution was sacrificed with using it, and after all any optics in between the sensor and the lens/subject is bound to have an impact-even at $300 USD retail.

So I downloaded a simple test pattern from Bob Atkins, and setup my 40D on a tripod and took a few rough test shots.

The first was taken with the tripod as far away as it would take to get the test printout to take up the full view of the camera while it was at maximum magnification (200mm, which is actually 320mm on the APS-C sensor). This yielded:

1/90 f/2.8 setting: 200mm (320mm)

I then affixed the 1.4x teleconverter, but left the lens set at 200mm. This means that the lens is at 200mm x 1.4 (teleconverter) x 1.6 (APS-C sensor factor) = 448mm. I did not move the camera or target, nor did I pull the lens out. This is an ‘in-between’ shot:

1/45 f/4.0 (you can’t go lower with the TC installed) setting: 200mm (448mm)

With the 1.4x teleconverter on, I now pulled the lens back to the 135mm setting, which made the target fill the screen as before in the first shot:

1/45 f/4.0 setting: approx. 135mm (1.4 x 135 = 189mm)

Summary?

I don’t see the difference in this casual test, do you? Can you tell which is which? I know I couldn’t get the exposures exactly the same, but the one on the left is without, and the one on the right is with the teleconverter.

Now a few qualifiers:

-The printout was on a 300dpi inkjet
-The lighting was not ideal (my stairwell), but I did use the internal, evaluative metering to 0 to ensure the exposures were identical (well, close!).
-Compression surely plays a factor with JPEGs see uncompressed versions below)
-Although I used a remote trigger for stability, there is always wiggle room for errors-but at least all my errors applied evenly to all pictures.
-To keep things like they would be in real life, I kept my Canon 77mm UV filter on for all tests. The camera is not new, but the lens, teleconverter and filer are.
-I did not make any attempt at balancing light temperature.

You decide!

uncompressed JPEGs, right off the camera (~2.8MB each):

Photo 1 – 200mm lens
Photo 2 – 200mm w/1.4x, zoomed
Photo 3 – 200mm w/1.4x, pulled back

If you have tests to share, let me know!

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