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X times ZOOOOOM - What does it mean?

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X times ZOOOOOM - What does it mean?

The first digital camera that I could afford, had 3 X optical zoom..... which , for me, was quite a leap from my Minolta 35 mm film camera of 30 years previous !... Since the 3 X optical zoom got a bit boring, I hankered for more ZOOM , and managed to save up for a Fuji S5600 with 10 X optical Zoom..... when that got boring, I got my present camera - Panasonic FZ28, with 18 X optical zoom......It has been very interesting over the past 4 years or so, but is now becoming boring !... so I`m looking for more ZOOOOOOM, and contemplating a Canon SX40 HS, with 35 X ZOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOM,  and the pics I have seen from it seem to be pretty good with about 90% less noise at full zoom than my Panasonic....
OK... so that is the history.... can anyone tell me what the "scale" is for measuring ZOOM.... i.e. if a bog standard camera with  zero zoom.... what is 1 X optical zoom doing in respect of measuring the focus point in front of the camera....ie. is it 1 metre? or what? 
I can understand that 60 mph is 2 X  faster  ( than 30mph).... and  120 mph is 4 X faster..... (etc.,) so how do you equate the ZOOM in respect of that analogy?
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Re: X times ZOOOOOM - What does it mean?

I Have no idea about the answer to your question but suspect the more you zoom in on something then the more stable your camera needs to be to get a good picture.
Some cheaper cameras have software that helps with image stabilisation and many of the more expensive lenses have image stabilisation built in but there is a limit to what these can do.
Therefore there must be a limit to the amount of zoom for an acceptable picture.
I Guess there is some mathematical formula  which would answer your question.
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Re: X times ZOOOOOM - What does it mean?

Para 1 & 2 .... totally agree.
last sentence....... I hope so... hence the posting !  Roll eyes
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Re: X times ZOOOOOM - What does it mean?

It's all referenced from the starting effective focal length.
In the case of the Canon you referred to it's effective focal length starts at 24mm and zooms to 840mm (24mm x 35 = 840mm) which is some zoom range.
http://www.canon.co.uk/For_Home/Product_Finder/Cameras/Digital_Camera/PowerShot/PowerShot_SX40_HS/
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Re: X times ZOOOOOM - What does it mean?

Yeah... I get that.... [ sort of ] but as I understand it.... 24 mm is "about" 1 inch... so 35 X 1" is ......... ? ( 1 Inch short of a yard)  (  Undecided  )
I suppose that means......... If I have an object 1 inch in size, at 1 yard.....  from the camera lens.... by going to max zooom (35 X) it will appear 35X bigger?
Is there a relationship between the amount of zoom and the distance (from camera) to the "object" ?  in a mathematical way?
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Re: X times ZOOOOOM - What does it mean?

Just to 'complicate it' without necessarily answering the question (not specifically anyway), the focal length is only fully meaningful if related to the image size (in the case of a digital camera the size of the CCD or sensor).  With 35mm film cameras anything below about 35mm focal length was considered 'wide angle' and 100mm or above was 'telephoto' with 50mm commonly being 'standard', with digital CCD sensors typically being much smaller than 35mm it needs a proportionately shorter focal length to get the same field of view.
Many digital cameras have the focal length of the lens specified 'in relation to' 35mm film rahter then the true focal length of the lens.
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pierre_pierre
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Re: X times ZOOOOOM - What does it mean?

not really the 24 is the focal length of the lens, i.e. the nominal point of focus from the centre of the lens to the initial point focus

Quote
The focal length of a lens is defined as the distance in mm from the optical center of the lens to the focal point, which is located on the sensor or film if the subject (at infinity) is "in focus". The camera lens projects part of the scene onto the film or sensor. The field of view (FOV) is determined by the angle of view from the lens out to the scene and can be measured horizontally or vertically. Larger sensors or films have wider FOVs and can capture more of the scene. The FOV associated with a focal length is usually based on the 35mm film photography, given the popularity of this format over other formats.

below results from a Cannon SX40
first looking towards church in 4x3 mode, the church  is just to the right of the brick house behind the white house.
wide angle 4.3  (~24 mm in 35mm lens)
then full manual zoom 15 0.5 (840 in 35 mm)
then with 4x digital zoom = 602 (3360 in 35 mm) noise what noise
then a cropped enlargement  from the 4x digital
the original images are 4000x3000, but cut to 1024 x 768
pierre_pierre
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Re: X times ZOOOOOM - What does it mean?

original of the full zoom 3360 at 4000x3000
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Re: X times ZOOOOOM - What does it mean?

Aha.... so I now understand, that the 24mm is the "(focal)" distance betweeen the lens and the sensor....
Thanks for the diagrams..... understand it a bit better...
PP... how far away is the church from your room?
Very impressed with the quality of pics from your Canon SX40 at that distance....  Smiley
pierre_pierre
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Re: X times ZOOOOOM - What does it mean?

measured on the OS map at just (nearly exactly)  one kilometre