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Old Oct 3, 2006, 2:51 AM   #1
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Hi all,

I have a Digimax S500 camera (samsung) and I get trouble in understanding the following number on the lens:

Zoom 5.8-17.4mm

(you could see the picture on the website below)

what does the number (5.8-17.4mm) mean?

As far as I know it is the range of focal length but on the website:

http://www.letsgodigital.org/en/news...tory_5633.html

They say that:

Digimax S500 digital camera features

- 3x optical zoom, 35 - 105mm (equiv 35mm camera)


so the focal length range must be: 35-105mm !!!???

Could any body help please?

Thanks alot!
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Old Oct 3, 2006, 6:03 AM   #2
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The actual focal length range (zoom range) of your camera is 5.8-17.4mm. Since the sensor in your camera is a lot smaller than a 35mm film frame, that zoom lens on your camera gives the same view as a 35-105mm zoom on a 35mm camera.
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Old Oct 3, 2006, 8:29 PM   #3
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Thank you very much Tom LaPrise. Your short but easy to understand explaination is great !!
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Old Oct 3, 2006, 9:58 PM   #4
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And in case you were not already aware.. the 3X optical refers to the magnification from wide ange. 5.8mm at wide angle so 5.8 x 3 = 17.4. You probably already knew that. You would be surprised though how many people think a high X number immediately means high magnification. I still have fun when people ask me what X zoom my 300mm 2.8 is and I tell them its just 1x
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Old Oct 3, 2006, 10:47 PM   #5
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Not at all, Windowmaker, the things you said are useful!

Anyway, I want to ask, is there any way to know what the focal length value is when I zoom in or out ?

E.g. : for my camera above, when I set

F 7.7
1/10

so, how do I know the focal length value?
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Old Oct 4, 2006, 12:35 AM   #6
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to Windowmaker : "3x zoom will magnify the subject of your image three times" right? (http://shopping.yahoo.com/optimizer/...pticalzoom.php)

so -> "high X number immediately means high magnification" is true !?

to all: about calculate the focal length

The f-numbers of my above camera are:

F 7.1 7.7 8.4 9.1 9.8 10.6 11.5 12.4

The higher the f number, the bigger I see the image zoom in, so I guess the bigger the focal length value (because when the distance longer the image projection is larger). That's mean, for 7.1 f-number is the minimum focal length: 5.8mm and for 12.4 f-number, the maximum focal length: 17.4mm.

Moreover,

f-number = focal length/ D

where D is the diameter of aperture.

From all aboves we get

7.1 = 5.8/D1 -> D1 = 0.82
12.4=17.4/D2 -> D2= 1.40

observe that D2>D1

But:the larger the f-number , the smaller the aperture size, so D2 has to be smaller than D1 (D2<D1) !!!

So it really confuses me

!?!?
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Old Oct 4, 2006, 6:40 AM   #7
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Focal length and f/ number are not the same things... often, the only way to know the focal length you used for a photo is to look at it on a computer and view the EXIF information. Many (most?) photo editing programs have either a button you can click or a menu item to show the EXIF information. As far as I know, no "point-and-shoot" or "prosumer" digital cameras have a focal length indication in the viewfinder. Just zoom until you're happy with what you see.

Regarding "3x zoom," all that means is that the focal length at the "telephoto" end of the zoom range is 3 times the focal length at the "wide angle" end. It doesn't mean the lens magnifies 3x compared to what you see with your eyes. Point-and-shoot and prosumer camera lenses start at a wide angle (some wider than others)--which actually reduces the image compared to what your eyes see--and go up to a telephoto focal length, which does magnify. So your "3x" zoom might actually only magnify the view by 2x or so (compared to what you see through your eyes) when you zoom in all the way--but that would be magnified "3x" what the camera shows when it's zoomed out (to wide angle) all the way.

nobtiba wrote:
Quote:
Not at all, Windowmaker, the things you said are useful!

Anyway, I want to ask, is there any way to know what the focal length value is when I zoom in or out ?

E.g. : for my camera above, when I set

F 7.7
1/10

so, how do I know the focal length value?
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Old Oct 4, 2006, 7:13 AM   #8
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The "f-numbers" you listed are lens aperture settings, not focal length.

You already understand what "f/" means (focal length divided by lens diameter) and that a larger f/ number (11.5, for example) gives a smaller aperture than a smaller number (7.7, for example).

"f" is focal length (and you won't see that number in your viewfinder); it's what you control with the zoom, and it controls how close or far away the scene looks. Usually, the only way to see what focal length you used is to look at the EXIF data for a picture, unless you have a digital SLR. (DSLR lenses have a focal length scale on the lens tube.)

"f/" is aperture. (You will see that number in your viewfinder.) It makes the image brighter or darker for a set shutter speed. Since the camera will usually keep the LCD at a constant brightness, you won't see the effect of aperture changes until you look at the picture on your computer.

That "/" is the source of your confusion...

nobtiba wrote:
Quote:
to Windowmaker : "3x zoom will magnify the subject of your image three times" right? (http://shopping.yahoo.com/optimizer/...pticalzoom.php)

so -> "high X number immediately means high magnification" is true !?

to all: about calculate the focal length

The f-numbers of my above camera are:

F 7.1 7.7 8.4 9.1 9.8 10.6 11.5 12.4

The higher the f number, the bigger I see the image zoom in, so I guess the bigger the focal length value (because when the distance longer the image projection is larger). That's mean, for 7.1 f-number is the minimum focal length: 5.8mm and for 12.4 f-number, the maximum focal length: 17.4mm.

Moreover,

f-number = focal length/ D

where D is the diameter of aperture.

From all aboves we get

7.1 = 5.6/D1 -> D1 = 0.79

12.4=17.4/D2 -> D2= 1.40

observe that D2>D1

But:the larger the f-number , the smaller the aperture size, so D2 has to be smaller than D1 (D2<D1) !!!

So it really confuses me

!?!?
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Old Oct 4, 2006, 9:49 AM   #9
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Another thing that seems to have confused you is what Widowmaker said about The "X" factor.

All that a 3x camera means is that the ration of the longest focal length and the shortest focal length.

But here is a perfect example why "3x" means almost nothing.
A 100-300mm lens is a "4x" lens, right? (400 / 100 = 3)
a 20-60mm lens is a "4x" lens, right? (60 / 20 = 3)

So those lenses would both be "3x" but they are *very* different lenses. The first is a long telephoto. The second is fairly wide angle to a little bit more powerful than the human eye (the human eye sees at around 50mm.)

But they are both 3x??? Almost useless information!
Look at the 35mm equivalent information. The lower the number is below 50mm the wider the angle lens. The larger the number is above 50mm the longer the telephoto. Then you just have to think about what *you* need (are you taking pictures of distent objects? Of wide landscapes? Taking portraits?

When you know what you want to take pictures of (even loosely) then you'll be able to figure out what you need in a lens.

Eric
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Old Oct 4, 2006, 10:35 AM   #10
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So is the lens diameter fix ? Or it changes when we change the f-number?

Assume that thebigger the f-number, the smaller the lens diameter.

And I know for sure that the bigger the f-number, the bigger the focal length (as I seethe imagezooms in). Moreover f-number = focal length divides the lens diameter



if the focal length is 16 times the pupil diameter, the f-number is f/16

(http://en.wikipedia.org/wiki/F-number)

So for my camera:

F7.1 means: f/D1 =7.1

with this setting I see the image totally zoom out -> focal length min = 5.8mm

or 5.8/D1 = 7.1 -> D1 = 0.82

the same forF 12.4

f/D2 = 12.4

with this setting I see the imageis full zoom-> focal length max = 17.4mm

or 17.4/D2 = 12.4 -> D2= 1.40

observe that D2>D1


or the bigger the f-number the bigger the lens diameter !!???
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