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Old Oct 14, 2011, 5:39 PM   #11
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G'day all

Thx to both ^
@TC - when I get workshop students with a Panny or Fuji or Canon with say, 15x zoom lens and we then compare its optical characteristics with a kit dSLR pair of lenses [ie- the primary aim of the sketch], if mr canon says that "this camera lens is the equivalent of 28mm to 330mm" and the dSLR lenses cover 18-55-300mm say, we go thru the motions of comparing AOV to demsonstrate that "substantially they are identical"

ie- that the 28mm [1x if you like] AOV is very close to 18mm on the dSLR; and that 300mm (12x if you like) show very similar results etc etc

Sure there are lenses [for various reasons] that don't 'fully' compare, but it is a workshop demonstration tool for beginners - which is what is was offered here for as well

Does this help ??
Regards, Phil
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Old Oct 15, 2011, 1:55 AM   #12
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And in general the wide end of P&S or superzoom cameras is around 28mm equivalent, though some are going as far as 24mm.

So within the context of X-times zoom, they are the divisor and therefore 1X.

The 35mm equivalent comparison is better but still misleading because it only shows equivalence of AOV, not of DOF, and gives no indication of likely diffraction limits at the sensor.

But to berate Phil for providing a handy rule-of-thumb chart that is easy to understand for beginners who aren't too interested in the details is not fair. I think it's a great chart.
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Old Oct 15, 2011, 3:29 PM   #13
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G'day all

@pp - thx for your comments too
I did have some extra thoughts from the wee-small-hours regarding the "1x - 3x etc" side of things and I am left to presume that 'maybe @TC does not have a P&S superzoom and therefore does not know that they display their zoom actions on a scale indicated by small display icons marked as 1x or 3x or etc etc' ... this therefore might be the source of his responses - all okay by me though

Following your feedback [thanx again] I have reviewed several of the dSLR 'equivalent' settings within the 18-55 lens range

And back to our OP - @Rusty who asked the very valuable Q in the first place ... mate - how do you find the chart??




Regards, Phil
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Old Oct 15, 2011, 3:42 PM   #14
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Many of us here have been working with cameras for quite a long time, and forget the difficulties we had understanding the relationships among the factors that make up exposure, depth of field, and field of view. A simple chart such as Phil provides, is a good starting place. I have learned from my own experiences in learning and teaching, that imparting too much information early on, can lose the attention of the student.
Good job on the chart.

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Old Oct 18, 2011, 9:25 AM   #15
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FYI, people have been coming here for quite some time, asking questions very similar to the one asked by rustyhill. They all left happy after learning the fact that there was no relationship between the zoom ratio and the focal length.

"X" is already badly overused. It's not just the ratio of the shortest focal length to the longest in zoom lenses. It's also the way of expressing the magnification power of an optical system compared to unaided vision (where unaided vision is 1X), frequently used in binoculars and microscopes, and wide angle conversion lenses have magnifications of, for instance, 0.5X or 0.65X. Many of the people that have come here in the past, thought that the zoom ratio, magnification, and focal length were all directly related. They all benefited from learning the truth.

This is the first time that anyone here has ever tried to gloss over the actual technical differences.
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Last edited by TCav; Oct 18, 2011 at 9:27 AM.
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