S100 vs. G1X - fast lens versus slow lens

Started Feb 7, 2013 | Discussions thread
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S100 vs. G1X - fast lens versus slow lens
Feb 7, 2013

Recently in this forum, a fellow photographer explained his preference not for the G1X but for the G15 due to the G15's faster lens which is "over two stops better" compared to the G1X. Challenging buying decisions in favour of one or the other camera is not my business. Putting the G1X in its true light isn't my job either although many of this negative comments on the G1X appear pretty weird to me.

There is an interesting question though: does the G15 outperform the G1X due to its faster lens ("over two stops better") because it gathers more light at f/2 compared to the G1X which is forced to operate higher f-numbers in the same shooting scene? The idea behind this question is the following: higher f-number = narrow aperture opening = less light = more noise, sounds obvious, doesn't it?

No, it isn't. The above questions and statements, the assumptions behind it, the method of comparison, all this is skewed, off-target and pretty useless for many reasons. I'll give you another example: a full glass of beer represents a longer drink than a half-full glass of beer, right? This sounds obvious but it is an incorrect statement because the amount of beer depends on the actual size of the beer glas (visit the Munich Octoberfest this year and you will know what I mean). The f-number doesn't tell you the amount of beer measured in litres but the percentage of beer relative to the actual size of the jaw - to be more precise: the f-number denotes the actual ratio of focal length and the lens' entrance pupil which are both lens specific properties, see http://en.wikipedia.org/wiki/F-number for more details. In fact, comparing f-numbers across various camera systems doesn't tell you anything about the image quality, image noise and about light gathering properties specific to this systems. We are all aware of this, we are all aware that a tiny P&S camera cannot compete with a FF camera in dim light, even if it can manage f/1.8 when the FF lens cannot. We are not aware of this fact, however, when discussing the G15 versus the G1X. I don't care who is buying what type of camera but I wish to understand why the discussion runs this way?

Sorry for chatting away. My intention for launching this post was different, I wish to demonstrate a test performend last night after having read the G1X-posts in this forum. The below images represent two cameras, i.e. the PowerShot S100 and the PowerShot G1X, respectively. Note that the S100 specifications are identical to the G15 in many aspects, e.g. 12.1 MP, CMOS sensor, Digic 5 processor and, most important, 1/1.7" sensor size. All images represent out-of-the-camera shots, two of them represent crops taken from the original files. Sorry for not providing fancy landscape images, I just dealed with subjects available in my office last night.

All images are noisy because they were taken in dim light, by purpose. Exposure time was 0.4s in both cases, by the way. The shameful G1X represents a slow lens (as i learned last night) indicated by the high f-number of 4.5. The very fast and bright S100 lens, on the other hand, shines with f/2 representing "over two f-stops better" than the G1X.

So, can you tell which image corresonds to what camera?

Image 1.1

Image 2.1

Image 1.2

Image 2.2

Let's unravel the mystery: image 1.1 and 1.2 represent the S100, 2.1 and 2.2 represent the G1X ... taken at a much higher f-number and, I haven't yet mentioned, taken at a much higher ISO. In fact, the ISO-setting was 400 with the S100 and was 1600 with the G1X. Thus, the G1X can easily compete with the 1/1.7"-cameras even with "dark" aperture settings and much higher ISOs.

Canon PowerShot G15
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