charles tabb Loc: Richmond VA.

I want to ask a question.
It's probebly a stupid one....

How can I convert 7X to mm for instance or reverse?
I keep looking at cameras that have say a 300 mm lens
or say it has a 7X zoom lens.

imagemeister Loc: mid east Florida

the 7x refers to the shortest focal length divided into the longest - another way they say this is a 7 to 1 zoom ratio - so with 300mm as the longest length, 50 would be the shortest.

RichardSM Loc: Back in Texas

Well 7x really means it is 7 times closers to the eye but in your case for mm it's about equal 250mm.

tsilva Loc: Arizona

7x just means the zoom goes from the widest focal length (whatever it is for the camera you are looking at) to 7 times that length. ie: 30mm to 210mm so here 30mm is the widest and we will call it "wa" so whatever the widest is for the camera you are looking at it would be "wa" x 7 = maximum zoom

MW

Actually, you can't convert the two. 7x means that the maximum focal length of a zoom divided by the minimum focal length equals seven. Obviously, there are literally an infinite number of combinations of max to min that equal 7.

You need more info to make a comparison. Not all manufacturers think it to their advantage to provide all the info you need.

Can you be more specific about what functional characteristic(s) you are imtetested in - perhaps the posters here could then provide a more useful response.

CO

The 7X refers to the zoom range. A 70-210mm lens has a 3X zoom range. 3 X 70mm = 210mm

Ched49 Loc: Pittsburgh, Pa.

Some fixed lens cameras have markings on the lens as to what that length is in mm. I don't know what the formula is. I do know that 7X is approximately 200 mm. Maybe someone will come around with a better answer.

CO

There might be a mistake. If 300mm is the longest and 50mm the shortest it would be a 6x.

imagemeister Loc: mid east Florida

Yes, SORRY so what is then then 40 something ???????

Linda From Maine Loc: Yakima, Washington

The Canon SX50 has an equivalent range of 24 - 1200 mm.

ken_stern Loc: Yorba Linda, Ca

Admittedly I'm in the deep end of the pool without summing lessons --- But here is my oversimplified understanding of the X magnification lens factor for the 35mm format ---- It's all based on the 50mm "normal lens" which more or less equals the human eye --- So a 50mm lens = 1x; a 100mm lens = 2x; a 300mm lens = 6x; a 400mm lens = 8x -- so on & so forth
I may be all wet but I'm "pretty' sure I'm not drowning

imagemeister Loc: mid east Florida

:thumbup:

imagemeister Loc: mid east Florida

You are correct for what you are saying -BUT- this is not what we are talking about ( the OP) ......although it is semi-pertinent and worth thinking about also.

ken_stern Loc: Yorba Linda, Ca

Sorry About That

blackest Loc: Ireland

This is an odd one I am not sure and I can't find an authoritative answer.
If anyone can provide a link to a reference that defines an answer.

The longest focal length divided by the shortest focal length on a lens doesn't sound right lets take a 75-300mm and a 25-200mm

well 300/75 = 4 and 200 /25 = 8

so the longer lens is 4x zoom and the shorter 8x that can't be right.

There is field of view 50mm lens on a 35mm camera is supposed to be around the same as the human eye. or if you look through the view finder you see things at the same size as with the naked eye.

That seems more meaningful as 300mm is 6x and 200mm 4x in 35mm terms.

28-80mm 35mm 18-55mm 1.5 aps-c and 14-42mm 2.0 m43 are pretty much equivalent lenses. on their sensor size.

These super zoom cameras have tiny sensors and very short focal lengths but are "equivalent" to massive full frame zoom lenses at least in terms of field of view.

so if we take actual 35mm lenses and put them on say a m43 camera
the 300mm is now a 12x zoom and 200mm an 8x zoom (on that body).

So does a magnification factor have any meaning without a frame of reference?

I look forward to seeing a definitive answer :)