How does a 1.4x teleconverter affect focal length on an APS-C Canon DSLR?
Asked 8/27/2014
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I’m trying to understand the difference between actual focal length and full-frame equivalent on a Canon APS-C DSLR with a 1.6x crop factor. If I use a 300mm lens, I know the field of view is often described as being similar to a 480mm lens on full frame. If I then add a 1.4x teleconverter, is the lens effectively 420mm, and does the field of view become equivalent to 672mm on full frame?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
11y ago
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The focal length of the lens system with a teleconverter will be 300mm (from the lens) * 1.4x (from the converter). This will give you a lens system with a focal length of 420mm.
Cropping of the image by the sensor from the full field of view to the APS-C size doesn't change the focal length... it just gives you the same field of view if you had a lens that was 1.6x longer on a full frame camera. This distinction is key when you start looking at the depth of field calculations and the like.
The focal length of the lens does not change if you go into photoshop and crop the image to a smaller size. Nor does it change when you use a sensor that is smaller than the image circle projected.
In this case, the field of view would be the same as that of a 672mm lens on a full frame camera (the lens system focal length * 1.6).
Originally by user13451. Source · Licensed CC BY-SA 4.0
user13451
11y ago
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Generated from our catalog & community — verify before relying on it.
Yes. A 1.4x teleconverter changes the lens’s actual focal length: 300mm × 1.4 = 420mm.
The APS-C crop factor does not change the physical focal length of the lens. It only narrows the field of view compared with full frame. So on a Canon APS-C body, that 420mm lens setup gives a field of view similar to a 420mm × 1.6 = 672mm lens on a full-frame camera.
So the key distinction is:
- actual focal length with teleconverter: 420mm
- full-frame-equivalent field of view on 1.6x APS-C: 672mm equivalent
This is why people say crop factor affects framing/field of view, not the lens’s true focal length.
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AI11y ago
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