Graphical representation of sensor sizes (or why PnSs don't do well at night)

[Groucho]

Sensor size is one of those things that is probably better shown graphically than just written down as numbers... so I threw together a little graphic showing the common sensor sizes and how they look next to each other. Eventually this'll be part of an article on my site.

The top is the size of a regular frame of 35mm film, also used by that rarefied beast, the full-frame DLSR. A medium-format DSLR like the Hasselblads use a sensor exactly twice this size.

APS-C is the standard size for DSLRs. The exact dimensions are for the Sony 6mp and 10mp sensors used in Pentax DSLRs, the same sensor in a Nikon or Sony DSLR is within one or two tenths of a millimeter. The Canon CMOS sensors as used in their non-FF DSLRs are slightly smaller, 22.2 x 14.8mm; not enough of a difference to bother with another graphic.

The rest of the sensors are a slightly different aspect ratio, hence the white bars. They are 4:3 versus the 3:2 of the 35mm and APC-C sensors.

The 4/3rds CCD is used in the Olympus and Panasonic DSLRs. The smaller size contributes to the higher noise levels seen from them as compared to other DSLRs.

Now we get to those darn point-n-shoot sensors... the 1/1.8" and 1/2.5" ones. There are others, but those seem to be the big two at the moment. Most PnSs use the smaller 1/2.5" sensor, with a few high-end ones going for the bigger one. Of course, bigger is relative - it's still puny compared to a DSLR sensor.

To get to the subtitle of the message title, this is a graphic demonstration of why PnS digicams do so poorly at night, and why more megapixels is not necessarily a good thing. The smaller the sensor, the less light they absorb. Combine that with trying to squeeze so many pixels out of them (often they are called on to produce just as many pixels as come out of the DSLR-sized sensors), and it's a recipe for disaster when it comes to getting good photos in low-light situations.

This also shows why a PnS digicam will generally produce much less clean photos than a comparable PnS 35mm camera.

Unfortunately, it's just not possible to stick a big sensor into a tiny little camera body like today's crop of pocket-sizes digicams - and the manufacturers believe (probably correctly) that people are more interested in a small camera than one that produces quality photos. And no major manufacturer has taken the risk of building a big-sensor PnS, which'd necessarily have to be a physically larger camera (to put in a bigger lens and put it farther away from the sensor.)

 

[ukcatfan]

The rest of the sensors are a slightly different aspect ratio, hence the white bars. They are 4:3 versus the 3:2 of the 35mm and APC-C sensors.

The 4/3rds CCD is used in the Olympus and Panasonic DSLRs. The smaller size contributes to the higher noise levels seen from them as compared to other DSLRs.

I totally forgot that the 4/3 system is a 4:3 ratio (duh ) That was another reason that I ruled them out when I purchased. I mainly do 4x6 prints, so it just saves me the step of having to crop every photo I want to print.

Kevin

 

[Pea-n-Me]

Nice to have an illustrated post in addition to a text explanation of sensor issues.

So am I to understand that the two small pictures on the left come from P&S cameras and represent the total resolution that each camera/sensor is capable of producing?

 

[Groucho]

No, the source photo is the same for each (and from my DSLR), just resized. For the photos, 10 pixels = one millimeter of sensor area. For example, the 35mm is 360 pixels wide, 240 high. The actual resolution depends on how much the manufacturer attempts to extract from the sensor. For example, my camera has the APS-C size sensor and my wife's Canon SD600 has the 1/2.5" sensor, but both are 6mp. Since the DSLR sensor has about 15x the area, it can produce significantly sharper photos, and perform vastly better in low-light situations.

Back to the duck photo, I just thought it might be helpful to have an actual image rather than just the usual white box.

 

[0bli0]

one of the things you might consider doing is showing the crop factors at the same focal length (like the one i did last year). also, you may want to illustrate the 'circle of confusion' and why smaller sensors mean greater depth of field at the same physical aperture and therefore worse bokeh (out of focus area). this would illustrate why p&s with small sensors are horrible for taking nice portraits.

 

[Groucho]

Some of that is getting beyond what I'm comforable trying to explain. Well, the crop factor is simple, but I haven't been paying attention enough to other people's explanation of the DoF on smaller lenses to be able to reliably repeat that info. At least, not yet...

 

[photo_chick]

Sensor differences are new territory to me. What about the differences in the manufacturing and data recording from a CMOS and a CCD? How does that affect image quality?

 

[Groucho]

Canon is the only major manufacturer to use CMOS instead of CCD sensors. Their sensors are a tiny bit smaller but have comparable image quality to the CCD sensors - Canonheads will point to them being better, but if they are, it's by an exceedingly small amount compared to the current crop of Sony sensors that sit in the Nikons, Pentaxes, and Sonys.

In other words, I wouldn't worry about it. Sensor size is far more important than whether it's CMOS or CCD.

 

[photo_chick]

Canon is the only major manufacturer to use CMOS instead of CCD sensors. Their sensors are a tiny bit smaller but have comparable image quality to the CCD sensors - Canonheads will point to them being better, but if they are, it's by an exceedingly small amount compared to the current crop of Sony sensors that sit in the Nikons, Pentaxes, and Sonys.

In other words, I wouldn't worry about it. Sensor size is far more important than whether it's CMOS or CCD.

So size does matter after all!

 

[Groucho]

I'm not touching that one with a ten foot pole. Or a nine foot, eleven foot, or any size pole!