 Jody E. Ellis |
Digitial Camera Optical Zoom X Ratings Can you tell me exactly what each increment of "X" means in the optical zoom ratings? Forinstance: if 7X = 200mm and 8X = 280mm, what does that mean for may photos? If an object is 8 yards away will it appear 1 yard away with 8X? Thanks
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Jon Close |
The multiple is usually just the ratio of the long and short focal lengths of the zoom. so a 28-200 zoom is a 7x zoom. To relate the magnification provided by a telephoto to that usually given for binoculars, you divide the lens focal length by the diagonal of the film image. For 35mm film the diagonal is 43mm (though 50mm is normally used for this calculation). So a 200mm lens is equivalent to 4x power binoculars.
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Jody E. Ellis |
John, Thank you for your reply but I'm still confused - if a 200mm lens is the equivalent of 4X - why do the digital camera makers say that a 200mm lens=7X and a 280mm lens = 8X? Sorry to be so dense but I'm missing a piece here.
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Wing Wong |
Something to do with the starting mm rating and the ending mm rating. For instance, 28mm-200mm is "7x" since 28mm times 7 is about 200mm. (196mm). It depends on what the starting mm(focal length) is compared to the ending focal length. So a camera that starts with 28mm and ends at 200mm will have a greater X rating than one which starts at 35mm and ends at 200mm, since it is "only" a 5x or a 6x. Hope that helps. :)
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Jon Close |
The 8x zoom is undoubtably 35mm-280mm. Actually, [just to add to your confusion ;) ] the lens is probably something like 7mm-56mm and the 35-280 is what its equivalent would be on a 35mm film camera.
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Wing Wong |
Jon's got a point. Most consumer digicams have a focal length multiplier of somewhere between 3x to 8x. Many Olympus digicams are in the 4x-6x range. Ie, a 35mm-200mm is really a 7mm-40mm. This is because of the sensor size. Hence the "equivelent 35mm size" notes on most digicams. With higher end digital cameras, the focal length multiplier is 1.6, 1.5, or none. Ie, what your lens says is the focal length really is the focal length.
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Jody E. Ellis |
Ahhh, I think I've got it - but good grief who thinks of these things! Next to the ppi versus dpi this is right up there on the confusing chart. Thanks everybody for 'clearing' this up. j.
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Davin Edridge |
Hello All, On this subject - perhaps someone can answer a quesiton for me - or set me straight - as the case maybe. Is this correct or incorrect? Regards,
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Wing Wong |
Digital cameras of all kinds depend primarily on optical focal lengths for their reach. The digital X or multiplier is merely cropping an image and resizing it in-camera. This consistently results in inferior images with artifacts. The source of alot of confusion is how advertisers and some camera makers refer to the "X" aspect. Some will use the #X to refer to the combined optical and digital reach. So if you have a 35-200mm optical system(7x) coupled with a "digital zoom" of 4x, then you supposedly have a combined 24X reach. In reality, you only have a 7X reach with software cropping. How do you determine? Look at the camera specs and look for the actual optical focal length ranges or the so-called 35mm equivelent focal length. If you find a camera that interests you, but you want to double check the real optical reach, find the camera model at reputable sites like: www.steves-digicams.com or www.dpreview.com or www.luminous-landscape.com to verify the camera specifications. I own a Minolta A1. It has a 7X optical lens system. It also has a 2X digital "cropping" zoom. Most places I've been to will only advertise the 7X portion, but some places have advertised it as a "14X" camera. My old camera, the Olympus C2100UZ had a 10X stabilized optical zoom system with 2x digital cropping zoom. I only ever used the optical system because the combined mode always gave me bad shots. For cropping, I use my computer and better sampling software to get a quality crop blow up.
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Wing Wong |
Correction: 24X should have been 28X. :) Additional note would be what some camera makers are calling "smart zoom". Basically, this is digital zoom, but with built-in limitors as to when it can or cannot be kicked in based on your image capture size. Example: 3x optical zoom 2MP camera. 4x digital cropping "smart" zoom. Because the digital zoom is essentially cropping your image, the effective MP rating of your camera goes down. So if the non-digital zoom cropping of your image is 1600x1200 at 2MP and with 4x digital cropping, only about 1024x768 is being exposed, the camera will only let you use that digital zoom if you have specified 1024x768 as the resolution you were shooting at. Short summary: smart zoom is in-camera cropping without resampling to a larger size.
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