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08/06/2005 08:23:41 PM · #1 |
Doing some internet research on lenses and found a post that said that on the 300D, a 28mm lens became 48mm when mounted. I've seen vague references to this sort of thing before, too, so:
1. Is this true? Do all lenses actually change when mounted on a camera?
2. Is there some formula for calculating the "true" length if this is the case?
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08/06/2005 08:31:32 PM · #2 |
Yes it's true. Multiply it by the crop factor to get the "actual" length, which in the case of the 300D is 1.6 I believe.
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08/06/2005 08:36:43 PM · #3 |
no it's not true. 24mm is 24mm.
The lens produces the same magnification no matter what body it's on. However, only the center portion of the shot is saved on a cropping camera. Because of this you think of the lens as if it were 1.6x longer, but it's actually not.
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08/06/2005 08:37:34 PM · #4 |
Digital cameras with sensors smaller than a 35mm camera's film plane essentially crop out a portion of the image that comes thru a lens. This gives the impression of a longer focal length. It is measured by the "crop factor" of each camera. For the 300D your crop factor is 1.6. 28mm times 1.6 equals a 35mm equivilent of 44.8mm.
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08/06/2005 11:59:23 PM · #5 |
Thanks for the explanation! The whole thing makes sense now.
Man, DPCers are great!
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08/07/2005 07:04:36 PM · #6 |
Originally posted by kyebosh:
no it's not true. 24mm is 24mm.
The lens produces the same magnification no matter what body it's on. However, only the center portion of the shot is saved on a cropping camera. Because of this you think of the lens as if it were 1.6x longer, but it's actually not. |
Does this mean that the view I see through my lens while framing the subject will be "cropped" to only save the center portion of the image and thus what I thought I was framing, actually was less in the final print OR that the view I see through the lens is actually the frame that will be printed, it is just that I am seeing less of the potential view due to the crop factor and would see more view if the lens were mounted on a film body at the exact same location.
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08/07/2005 07:13:55 PM · #7 |
Originally posted by Flash:
Originally posted by kyebosh:
no it's not true. 24mm is 24mm.
The lens produces the same magnification no matter what body it's on. However, only the center portion of the shot is saved on a cropping camera. Because of this you think of the lens as if it were 1.6x longer, but it's actually not. |
Does this mean that the view I see through my lens while framing the subject will be "cropped" to only save the center portion of the image and thus what I thought I was framing, actually was less in the final print OR that the view I see through the lens is actually the frame that will be printed, it is just that I am seeing less of the potential view due to the crop factor and would see more view if the lens were mounted on a film body at the exact same location. |
WYSIWYG for the most part. However I don't think your camera has 100% coverage on the viewfinder, but that's something different.
edit: yes less potential view, you're not seeing 100% of what the lens puts out, only the center.
Message edited by author 2005-08-07 19:15:11.
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08/07/2005 07:24:13 PM · #8 |
Originally posted by kyebosh:
edit: yes less potential view, you're not seeing 100% of what the lens puts out, only the center. |
I felt that the view I am framing or seeing through the lens is in actuallity (within a couple percent)the view that gets printed, so even though the statement that a 24mm is a 24mm regardless is accurate, it is also true for the sake of understanding that a 24mm will "view" like a 36mm and the print will be like that of a 36mm lens. The crop factor influence on the lens focal length is in fact the "view" that the fotog is seeing and not a cropped center of the image that they thought they shot.
Just wanted to clarify.
Thanks.
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08/07/2005 07:59:46 PM · #9 |
From what I understand this explains the crop factor 35mm frame vs. Digital with focal length. If I'm wrong let me know.
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08/07/2005 11:16:46 PM · #10 |
| Think of it this way... your lens focuses the image onto a photo-sensitive surface (film or sensor). The sensors on all but the most expensive DSLRs are smaller than 35mm film, so they only capture a cropped area compared to film. When the captured image is viewed, the smaller frame must be enlarged more than 35mm film to achieve the same print size. Thus, you are cropping and enlarging the scene- effectively the same as using a longer lens to zoom in closer. This is the crop factor, and it means that any lens will appear to be longer (1.6x longer on the Canon 350D, 1.5x on a Nikon D70, 2x longer on an Olympus eVolt, etc.). The smaller the sensor, the greater the crop factor. The same principal applies to other digital cameras and cell phone cameras, but since the lenses aren't interchangeable, the manufacturers simply list the 35mm equivalent for those. |
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