One hundred forty divided by fourteen =?
Asked by
rebbel (
35553
)
April 1st, 2018
Ten, right?
So, here’s where this is coming from: I have a camera, with two lenses.
One lens (wide) goes from 14 to 42 mm, the other one (tele zoom) from 40 to 150 mm.
(I know that in the question title I speak of 140, but bare with me)
The first lens has a magnification factor of 3 (14 times 3 is 42).
The other lens has one of, roughly, 4 (40 times 4 is 160 (I know, not 150, but again, bare with me)).
So, the two lenses together go from 14 to 150 mm (roughly 10 times magnification).
Then why do I think they have only 7 times magnification (the 3x (wide), added to the 4x (tele zoom)?
Where do I go wrong?
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7 Answers
It’s not magnification. The mm’s are in relation to the aperture and lens.
“A 55mm lens, for example, on a 35mm camera, can take in an angle of view of 45 degrees; the 35mm wide angle lens for the same camera has an angle view of 64 degrees; while the 135mm telephoto lens has an angle of view of 18 degrees.” from The Amateur Photographer’s Handbook, by Aaron Sussman, 8th ed, 1973
Want to know more about cameras and take better pictures?? Get a copy of this book, sometimes known as The Photographer’s Bible.
@kritiper Thank you for your answer.
And for the book recommendation.
I should have maybe written “zoom factor” instead of “magnification”.
Maybe my question was more one about calculation, rather than photography, in hindsight.
If we purely look at the numbers in my question, why doesn’t it add up (for me).
Why do I reach 7, but also 10?
I don’t know anything about cameras, but if one lens acts on the input from the other then the total magnification would be 3×4 = 12. If you magnify something that is 1 inch by a factor of 3 then the image would be 3 inches. If you now magnify the 3 inch image by a factor of 4 then you get 12 inches.
I don’t have the math at hand, but I do understand one thing about this question that’s easy to respond to:
Your 14–42 mm zoom lens is specifically made for fish-eye / wide-angle shooting. “Normal” focal length on a 35mm type camera is ~50mm. That is, the distance from the centerline of the lens plane to the film (or sensor) surface. So that would be your “1” position.
The 40–150 mm zoom is for that “normal” position to a “zoomed” or enlarged focal length of 150 mm, which is essentially three times “normal”.
I can’t say for sure whether the focal length has anything to do with the magnification factor (it would seem reasonable to assume, but I wouldn’t bet on it).
Also, “bear”, not “bare”, in this usage.
42 divided by 14 = 3
150 divided by 40 = 3.75
Your answer is 6.75, not 10
As @kritiper says: 14 to 42 is 3x, and 40 to 150 is 3.75x. Total would be 3*3.75 = 11.25x, but there is a bit of overlap (40–42) so if you went from 14 to 150, it would be 10.7x
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