What does it mean to 'couple' Canon EF-S 18-55mm and 55-250mm lenses on a 550D?
Asked 6/24/2013
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A review says that when the Canon EF-S 55-250mm IS is 'coupled' with the EF-S 18-55mm IS, you get an effective range of 29mm to 400mm. I’m using a Canon 550D and I’m confused about what that means. Are these two lenses used together at the same time, or does it just mean swapping between them? How does the 29-400mm range relate to the 18-55mm and 55-250mm focal lengths on a crop-sensor Canon body?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
13y ago
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In this instance they are merely referring to taking both lenses with you and using them interchangeably to provide continuous coverage from 18 - 250mm. The article uses the word "effective" to indicate the full frame equivalent range of 29 - 400mm, which covers the vast majority of photographic subjects.
There are types of lenses that can be coupled, for example teleconverters can be coupled to regular lenses to increase the focal length. The coupling is accomplished by the teleconverter having a standard lens mount on the front - teleconverters cannot be used to take images by themselves as they are unable to focus an image onto the sensor.
Another type of coupling that occurs with regular lenses is reversal of a wide angle lens in order to produce a high magnification macro lens. A wide angle lens is usually mounted onto a normal lens by the use of a reversing ring, which screws into the filter threads on each lens.
Originally by user1375. Source · Licensed CC BY-SA 4.0
user1375
13y ago
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In that review, “coupled” does not mean mounting both lenses together. It simply means using the two lenses as a pair and swapping between them when needed.
On your Canon 550D, the EF-S 18-55mm covers wide to normal views, and the EF-S 55-250mm covers telephoto. Together they give you continuous coverage from 18mm to 250mm.
The review’s “effective 29mm to 400mm” is the 35mm-equivalent field of view after applying Canon APS-C’s 1.6× crop factor:
- 18mm × 1.6 ≈ 29mm
- 250mm × 1.6 = 400mm
So the lenses are not optically combined; you just carry both and change lenses depending on the shot.
There are accessories that do physically combine with lenses, such as teleconverters, but that is not what the review is describing here.
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