bleirer

I ask this as a hypothetical because I don't want to get into debates about camera brands or models. Suppose I have two raw files, both 24 megapixels, both with the same subject filling the frame, both with "Normal" lenses, shot with identical exposure. All other conditions identical.

What differences in image quality would I expect between these two files based only on the difference in sensor size? What about enlargement, would there be differences in quality of an enlargement based only on the sensor size difference?

I've read that in enlargement the larger sensor would be better because it would not have to be enlarged as many times as the smaller sensor due to the larger original area, but this doesn't make sense to me if the smaller file has crammed in the same number of megapixels and the full image fills the frame and covers the subject with the same number of pixels. I thought pixels were dimensionless once they were in a raw file.

bsprague Loc: Lacey, WA, USA

As the owner and operator of a smaller sensor 20 MP camera, my sense is that there will be little difference as long as there is plenty of light. In lesser light there will be more noise and maybe a little less dynamic range with the smaller sensor. The other operational factor is bokeh. You can get more with a bigger sensor and the lenses that go with it.

That said, nobody that looks at my prints ever says, "Wow, what a small sensor!"

I'm anxious to see what others say.

Ysarex Loc: St. Louis

The smaller sensor image will be noisier. Larger sensor = less overall noise all else being equal.

Joe

CHG_CANON Loc: the Windy City

Pixels do have a size, just not a standard size. So, 24MP on a DSLR is 6000x4000 pixels, regardless of sensor size, assuming a 3x2 aspect ratio. The cropped sensor 24MP means these pixels have to be physically smaller to fit into the smaller geography of the cropped sensor as compared to the same 24,000,000 pixels (24MP) found on the full-frame sensor geography. Consider a 'meter' that is a fixed distance standardized to the wavelength of a certain color of light. 1-meter means always the same distance in all situations and uses. A pixel doesn't have this standardized size like a 'meter'. Rather, a pixel is the smallest unit of a digital image (or graphic) that can be displayed and represented on a digital display device. The device size (whether a 4K High-Dev display or 22.3 × 14.9 mm APS-C format sensor) determines the 'size' of the pixels as used for that device. The meaning of 'pixel' also depends on context where it may contain three or four colors, and depending on the bit depth, may represent 2-bits (black & white) to 24-bits (16,777,216 colors).

To your question, you might find this discussion and demonstration useful. Note the effort to achieve the same 'framing' using different focal length lenses to the same subject from the same distance using cropped vs full-frame lenses: https://neilvn.com/tangents/full-frame-vs-crop-sensor-cameras-comparison-depth-of-field/

To the phrasing of your question, as shown in the examples in the link above, your sample images would not be the same simply standing in position x at distance y from subject A and simply swapping the same lens between a cropped and full-frame camera, while keeping the same exposure. One should appear to be the 'cropped version' of the other, with no other material visual difference, particularly at a low ISO like ISO-100 on both cameras. As show above, there will be subtle (very subtle) differences in the depth of field that are hardly noticeable outside of specialized situations.

Printing / enlarging the digital file is another place you'll expect to find differences between the two 24MP sensors. But here, I have to differ to a description I've seen Gene give to explain these differences. I almost understand the theory, but not to the extent I can explain in words or cite a good example.

RichardTaylor Loc: Sydney, Australia

What ISO value are you shooting at?
From personal experience, for ~ same generation cameras the larger sensors will have better higher ISO performance.

bleirer

That's the reason I said both would have a 'normal' lens for their format, with the idea that the same subject would fill the same sensor area. I'm mainly wondering about the idea that greater sensor area independent of other factors accounts for a quality difference.

bleirer

Lets say they are both at ISO 100?

BebuLamar

The smaller sensor image has more noise and more depth of field.

bleirer

Interesting, the reason I've read for that is because the lens required for the larger sensor would require a larger lens with the actual size of the aperture being physically larger, pupil passing more light, even though the f-stop number would be the same by ratio.

User ID

Exactly as say. Digital files are not film negs, they
have NO physical dimension to "enlarge". Whoever
wrote what you read about enlargement is just an
"Internet Expert".

FWIW I concur with much of the other replies that
in good light at low ISO sensor size is meaningless.

Acoarst this thread also contains the bokeh myth
about sensor size. Bigger sensors have the same
bokeh as small ones at any given aperture size.
Thaz a well tested fact. But aperture size is NOT
f/stop numbers. Equip two camera with lenses of
the same angle of view. One is FF and the other
is m4/3. Set the FF to f/4 and the m4/3 to f/2.
This will result in equal aperture sizes and equal
bokeh. The bokeh myth ignores aperture size and
instead looks only at f/stop numbers.

The smaller the format, the shorter the lens FL at
any angle of view. This results in faster lenses
being available for smaller formats at any given
range of expense and also of physical size.

CHG_CANON Loc: the Windy City

That's the wrong word (normal) that just exasperates a general misunderstanding between 'equivalent field of view' with 'equivalent focal length'. The question / assumption is further exasperated by 1.5 vs 1.6 crop factors for different brands of cropped sensors. The prior linked example attempted to find two Nikon primes that come out to the same equivalent field of view while maintaining the same f/1.4 maximum aperture.

If we remove the 'how' / 'what lens' technical aspects of the question, the visual differences are in the out of focus areas, if any. One would expect some noise differences, more pronounce the higher you get away from base ISO for the two cameras.

When you consider the sizes of the sensors, this idea of magnification to get to the same print size should (could) magnify the noise in the image from the cropped-sensor by a larger factor to get to the same print-size. This issue is going to be more noticeable at higher ISO values, in theory, but this generalization would have to be demonstrated by specific / actual 2019 comparisons of equipment to confirm.

I prefer published examples rather than generalized expectations, such as this additional example of the same question: https://petapixel.com/2017/10/03/full-frame-vs-crop-sensor-shootout-can-tell-difference/

bleirer

That's the thing, I've read the part about enlargement from several sources that I trust, so thats mainly why I'm asking.

RichardTaylor Loc: Sydney, Australia

Probably very hard to tell the difference, at least for scenes that do not have a high dynamic range.

Ysarex Loc: St. Louis

6000 pixels is 6000 pixels and they're going to enlarge/print the same. But before they became equivalent pixel counts they were different size pixels behind different lenses. There are real physical realities of lens resolution and are we making sensors now with pixel resolutions that exceed the res of the lenses in front of them?

No easy answer: https://luminous-landscape.com/do-sensors-out-resolve-lenses/

Joe

User ID

Exactly.

Thaz why f/stops are not transferable between
formats. You hafta stick with absolute aperture
size, and ignore relative apertures [which are
called "f-stops"].

97% of Hogsters do not really know what an
f-stop really is. But, they will endlessly parrot
mythologies circulating in their technological
circle jerks. This is NOT a UHH phenomenon.
The web is loaded with "expert" bloggers and
half baked ignorant tutorialists.