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Jeff
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Jeff
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 Mon Jun 29, 2015 6:51 pm |
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mike
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mike
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Mon Jun 29, 2015 7:28 pm |
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yes, if the are used on the same body.
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Bedivere
Why Do Witches Burn?
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Bedivere
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Mon Jun 29, 2015 9:00 pm |
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Jeff - you are correct. Smaller number = wider field of view, larger number = narrower field of view. Same number on two different lenses will take essentially the same picture. The two lenses may have some individual characteristics (distortion & such) that would cause the pictures to be slightly different but you wouldn't be able to tell without comparing them side by side.
The size of the sensor can affect the apparent focal length, that's why mike added the disclaimer about using the same body.
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Backpacker Joe
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The main consideration these days is knowing whether youre camera has a full framed sensor. If it does the lens values are accurate and true.
My Canon 5D is full framed so an 11-24mm lens is just that. Many cameras are NOT full framed, as those sensors are so expensive. So, on a cropped sensor camera that 11mm lens is going to be a 17mm lens, etc etc.
"If destruction be our lot we must ourselves be its author and finisher. As a nation of freemen we must live through all time or die by suicide."
— Abraham Lincoln
"If destruction be our lot we must ourselves be its author and finisher. As a nation of freemen we must live through all time or die by suicide."
— Abraham Lincoln
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Cyclopath
Faster than light
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Cyclopath
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Tue Jun 30, 2015 9:09 am |
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| Jeff wrote: | | I've always assumed that a lower lens focal length corresponds to a wide field of vision and a longer length has the effect of zooming in. |
Yeah, for an extreme example think of a telescope.
Any lens is gathering light from the outside world and focusing it on something (like a slide of film, or a CMOS chip). With cameras, the bigger the film or chip, the bigger the glass needs to be to do the same job, to project and focus an image that covers the chip to record a photo.
On a 35 mm film camera (or a full frame digital) a 24 mm is a pretty wide angle, but on a compact digital camera with a much smaller chip that same 24 mm can be an extreme telephoto. In either case, the lens is 24 mm away from the film plane; making a big or a small circle from this distance determines how much of the scene goes into that circle.
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mike
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mike
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Tue Jun 30, 2015 10:48 am |
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| Backpacker Joe wrote: | | ....a full framed sensor. If it does the lens values are accurate and true...... So, on a cropped sensor camera that 11mm lens is going to be a 17mm lens, etc etc. |
Not true BPJ. Focal Length is determined by a mathematical formula. f number is different but related. Check out Wikipedia. What you are talking about is apparent FOV (field of view) which indeed is different for different sensors. "True" focal length is a hold over from film days and really means "equivalent FOV to traditional FL".
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gb
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gb
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Tue Jun 30, 2015 1:42 pm |
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Gray
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Gray
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Wed Jul 08, 2015 12:19 pm |
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Another thing to keep in mind is that some lenses are specifically built for cropped-sensor cameras, and as such their listed focal length is WYSIWYG, and they will not work properly (or at all) on a full-frame camera.
Some examples, all using Canon, since that's what I shoot.
My Rebel T1i is a crop-sensor body, and like most (all?) Canon crop sensors is a 1.6 crop.
A rented 5D is full frame.
Canon has 2 lens designations: EF and EF-S. EF-S is specifically for crop-sensor bodies (and usually cheaper/plastic), they will not work on full frame bodies. EF lenses will work on both full frame and crop-sensor bodies, but will behave differently.
I have a Sigma 10-20mm wideangle lens (EF-S) that is specifically for crop-sensor cameras. On the T1i, it is a true 10-20mm. On the 5D, it works, but you see the image circle, and would need to crop down to 1.6 to get a usable picture.
A Canon 50mm f/1.4 (EF) on a full-frame body will produce true 50mm images/FOV. The same lens on my T1i will produce a FOV of (50mm x 1.6) 80mm. So, on a crop-sensor, the field of view will be similar to the FOV of a 80mm lens on a full-frame body.
--Gray
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