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Comparison "teleconverter vs. interpolation"
All pictures were taken with the Canon 300mm f/2.8 L IS USM on a 40D from a tripod.
IS off, MLU, timer and manually focused using LiveView. Distance ~5m.
There might be a slight difference in size because teleconverters never exactly magnify by factor 1.4 or 2.0.
As I only took one frame each time there is no guarantee that all are 100% shake-free.
First of all a comparison of the different focal lengths at different appertures
(click for 100% view - 1530x2040px, 3 MB)
Comparison of pictures with converter vs. shorter focal length and resizing
300mm resized vs. 420mm with converter (wide open)
(click for 100% view - 2000x1000px, approx. 1.8MB)
300mm resized vs. 420mm with converter (stopped down one stop)
(click for 100% view - 2000x1000px, approx. 1.8MB)
420mm resized vs. 600mm with converter (wide open)
(click for 100% view - 2000x1000px, approx. 1.8MB)
420mm resized vs. 600mm with converter (stopped down one stop)
(click for 100% view - 2000x1000px, approx. 1.8MB)
600mm resized vs. 840mm with converter (stopped down one stop)
(click for 100% view - 2000x1000px, approx. 1.8MB)
600mm resized vs. 840mm with converter (stopped down two stops)
(click for 100% view - 2000x1000px, approx. 1.8MB)
300mm resized vs. 600mm with converter (stopped down one stop)
(click for 100% view - 2000x1000px, approx. 1.8MB)
My conclusion:
- The two converters stacked are not a good deal but it might just be a problem with these specific ones. Two Canon or Sigma TCs might be better.- In a "controlled" environment you can use a 300/2.8 as a virtual 420/2.8 by resizing without losing too much quality.
- under field conditions and with the right amount of post-processing converters should always beat resizing and of course they allow you to crop (only without the advantage of an extra f-stop)