mm to "x zoom" conversion

Started Apr 14, 2006 | Discussions
fandsen New Member • Posts: 14
mm to "x zoom" conversion

Just wondering, approx. how many mm's equate to a 3x, 6x, and 12x zoom respectively? And is it correct that this number would be multiplied by 1.6 when the lens is placed on a 350d? Thanks in advance.

Evan

Chris Hackney Regular Member • Posts: 142
Re: mm to "x zoom" conversion

It does not equate with any particular 'mm'. X3, X10, X12 etc just tells you how many times longer the focal length of the lens is on full zoom than it was at minimum zoom. So, a X3 lens with a minimum focal length of 24mm would have a maximum zoom of 24 X 3 = 72mm. A X10 lens would have a maximum focal length of 24 X 10 = 240mm and a X12 lens would be 24 X 12 = 288mm. Of course if your lens had a minimum focal length of let's say 10mm then a X3 zoom would have a maximum focal length of 30mm; X10 of 100mm and a X12 zoom would have a maximum focal length of 120mm.

The answer to the second part of your question is yes, because a full size 35mm frame is 1.6 times the size of the sensor in your 350D. I hope this helps.

Chris.

Dave008 Junior Member • Posts: 39
Re: mm to "x zoom" conversion

There is no standard conversion. In the world of P&S photography, the x zoom factor is relative to the range of the camera. For instance, a 28-280mm lens would be called a 10x zoom lens. A 35-350mm lens is also a 10x zoom lens. In these two cases, the maximum telephoto focal length is simply 10 times the wide angle focal length, hence 10x zoom.

josh_h Forum Member • Posts: 51
Re: mm to "x zoom" conversion

there is no x mm = y zoom conversion. What it is, is the longest zoom of the lens divided by the widest zoom. For example, the kit lens is 55/18=3.06 zoom (3X). The 70-300mm is 300/70=4.28 ( 4X).

As for the 1.6 multiplication factor, it does not affect the zoom (ie 3X, 4X, etc) since all focal lengths are multiplied. (55*1.6) (18*1.6) still equals 3.06, however your lens is the equivalent of a 28-90mm lens.

JSug Contributing Member • Posts: 654
Re: mm to "x zoom" conversion

fandsen wrote:

Just wondering, approx. how many mm's equate to a 3x, 6x, and 12x
zoom respectively? And is it correct that this number would be
multiplied by 1.6 when the lens is placed on a 350d? Thanks in
advance.

There is no such conversion. The 3x, 6x, 12x etc. that you see on fixed-lens digicams is a ratio. They've taken the longest focal length and divided it by the shortest focal length. The problem with this is that it doesn't tell you anything about about what the actual focal lengths are. For instance, a 10x zoom lens could be 24-240mm or it could be 10-100mm. Those different values will give you vastly different view angles. So two cameras that are both labeled as 10x zooms will not necessarily have the same focal length range.

The 1.6 crop factor is simply a way of comparing the viewing angle of a 300D/350D to the same focal length on a full-frame 35mm camera.

See these glossary entries for more detailed explanations:
http://www.dpreview.com/learn/?/Glossary/Optical/Focal_Length_01.htm
http://www.dpreview.com/learn/?/Glossary/Optical/Focal_Length_Multiplier_01.htm

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Jordan

OP fandsen New Member • Posts: 14
Re: mm to "x zoom" conversion

That makes much more sense, thanks for the speedy replies guys.

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