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< Esato Forum Index > Sony Ericsson / Sony > General > what is the meaning of '3.8mm, 1:3.2' Bookmark topic

you can see these specs on the back of a camara near the lens. what is the meaning??
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Posted: 2007-05-29 12:29:00
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yeah and what difference does it make that its 3.8mm or 4.2mm
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Posted: 2007-05-29 12:32:42
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from what I understand...

3.8mm is the focal length

1:3.2 is the aperture size, or in this case its the ratio of focal length to effective aperture diameter which is also known as the f-stop (f/3.2)

please read those pages for more detail on what it all means
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Posted: 2007-05-29 13:19:52
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from the above link what i understand is
- the more the shutter speed, larger will be the aperture size means more costly.
- if we hav smaller aperture size, shutter speed will hav to be slow. means that a 1:3.2 (w610) hav the slower shutter speed than 1:2.8(w810) if both hav same aperture size. but if we assume that the '3.8mm' is the aperture size then both hav same shutter speed. (3.8x3.2 roughly equals to 4.8x2.8 )
what you say.

[ This Message was edited by: ajeetpv on 2007-05-29 13:07 ]
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Posted: 2007-05-29 14:04:00
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Almost.
A lens with a small value (1:2.8 or f/2.8) is better than a lens with a higher value(1:3.2 or f/3.2) since it is capable of letting in more light to the film surface or ccd element, and thus, more expensive. Having the possibility to let in more light allows for shorter exposires, i.e. higher shutter speeds, with thh same sensitivity on the CCD. However, a large aperture opening only allows for a shorter range of focus, so it is always a good idea to keep the aperture opening small, ie a high aperture value.

The focal length has nothing to do with the aperture value, other than zoom lenses with large focal length often tends to contain more lenses, and thus let less light through, i.e. have higher apertures.

On a standard SLR camera, with 35mm film, a lens with about 50-55 mm focal length is considered a 'normal' lens, while lower values are "wide angle", and when you get below 15 mm, we are talking fisheye. Telescope lenses are lenses with focal lenghths above 55 mm.

When it comes to focal lengths in digital cameras, and especially cameras in mobile phones, the size of the surface of the CCD is much smaller than the 35x47 mm the SLR has, and the length of a "normal" lens is smaller in the same proportion as the dimensions of the CCD compared to the SLR, so I would guess that a 3 or 4 mm lens on a mobile phone is not a fisheye, but still a wide angle lens. The K800i has a 5.2mm/1:2.8 lens, and that is comparable with a 35mm lens on my old Canon EOS 350 SLR (non digital), which is 50mm/3.5. According to that, the surface in the K800i's sensor is about 1/10 of the EOS. (Should I put that lens on an EOS 400D, the lens would be somewhat telescopic, since the surface of that sensor is about half the size of the non-digital EOS.)
A zoom lens has the possibility to change the focal length by having several lenses that are moved back and forth to/from each other.

(d*ned smilies, I had to edit to remove the 8) smilie)

[ This Message was edited by: altemyr on 2007-05-29 15:20 ]
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Posted: 2007-05-29 16:18:54
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Thanks for the very useful post! It's certainly enlightened me a bit.
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Posted: 2007-05-29 16:47:00
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So when comparing 3.8 to 5.2mm lens,the 3.8 will be like a wide angle ,where as 5.2 is more nearer to 'normal' lenses.I hope my interpretation isnt wrong.
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Posted: 2007-05-29 17:15:12
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Yes, but only of the areas of the photo sensors are the same. A digital zoom works like that: in largest zoom position, only a small surface in the middle of the sensor is used, and thus, the pixel resolution becomes smaller. You can do the same in your computer instead by enlarging a part of the picture.
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Posted: 2007-05-31 09:42:18
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now there are some confusions *for a 3.8mm 1:3.2 the aperture size would be 3.8x3.2 ?
*for larger aperture size we get clearer picture of nearer objects?
* with specification provided 3.8mm 1:3.2(w610) & 4.2mm 1:2.8 (w810) for two phones what conclusion can we get? (aperture size of later is slightly larger than former?) or which phone has better camera?
*can we calculate the shutter speed?
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Posted: 2007-05-31 11:04:00
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I'm not an expert on the subject, but this is what I know.



No, 3.8 is the focal length and has nothing to do with the aperture.
Only 3.2 determines the aperture size (the smaller value, the larger aperture).



Sort of. A larger aperture has a more shallow depth of field (DOF) meaning the object in front appears more sharp than the background objects. If you take a picture on a close object, with a larger aperture size the background objects becomes more fuzzy than with a smaller aperture size.

Compare the pictures of the flower in the link below to see the difference.

http://www.photoxels.com/tutorial_aperture.html

Larger aperture size also means better night shots (if the sensor is adequate), less effect of shaky hands and easier to catch fast moving objects.



Generally speaking since its easier to take good pictures with a larger aperture size, W810 is the better one. W810 also supports AF meaning you can take sharp pictures at different distances of close objects while
w610 only has one "perfect" distance for close objects.



If you mean max and min shutter speed, the answer is no.


[ This Message was edited by: Arne Anka on 2007-05-31 10:58 ]
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Posted: 2007-05-31 11:56:07
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