Taking large detail pictures in crop Body??

rickp

I've come across some reference to a crop sensor creating a bit more image than full body sensors. I also came across some reference to taking images in Medium quality size on a crop body relieves the camera of cramming so much information and thus improving quality a bit.

Is this accurate or am I getting information from different ends of the stick.

Thanks
R.

photokandy

Your second point first: Medium gives better quality? Um. No. You're only throwing away information that you might need later. Always, always (unless speed or size is an issue) shoot to capture the most information possible. That means use the highest resolution and the highest quality of resolution. (Better yet, shoot RAW. And not small RAW -- full resolution.) You might need all those bits of information, after all, once you get to post-processing.

First point: Crop sensors are smaller than their Full-Frame counterpoints and so discard more of the image circle projected from the lens. So in a small way, crop sensors can sometimes look like they generate better image quality, but only because they are using what is usually the best part of the lens -- the center.

It's also possible, depending upon the comparison sensors, that the crop sensor has more pixels-per-inch than the full-frame sensor, thus resolving a tad more detail than the other sensor would render. (But you have a trade-off: More pixels per inch means more noise.)

That said, if you took a crop sensor and a full-frame sensor with exactly the same pixels per inch, and looked at the images produced, the full-frame sensor would have a wider field-of-view than the crop sensor, but if you cropped the FF's image, you'd find the two images to be identical.

rickp

photokandy,
you kind of touched on the point that kind of confused me. Packing so much info on a crop sensor creates more noise.

So let me ask you, taking the same image with a full size body and a crop body wouldn't the full body have better IQ based on the above statement.

The reason I ask this is because I'm trying to figure out why so many people like the 5D and 1D series Cameras?
I've read their info on the Canon website and people seem to always have good things to say about them and one point I keep reading is the full body feature.

R.

photokandy

All things being equal, a sensor with more megapixels will have more noise.

Problem is that most all things aren't usually ever equal.

So, let's compare the 5D Mark II, the 1D, the 500D and 550D (t1i/t2i):

5Dmk2: 2.4mp/cm^2 (21mp, FF)
1Dmk4: 3.1mp/cm^2 (16mp, APS-H)
500D: 4.5mp/cm^2 (15mp, APS-C)
550D: 5.4mp/cm^2 (18mp, APS-C)

So, right off the mark, the ppi is different for each sensor. The 5Dmk2 has great image quality because they squeeze only 2.4mp per square centimeter, and as such each pixel is a bigger bucket for light.

That said, the smaller pixels may render more detail because there's more of them packed in a smaller space. But noise will play a role in how much more detail one could expect to see. Plus, there's also the lens that starts to get in the way -- not all lenses can focus light down to those tiny pixel sizes.

And then you get to the design of the pixel itself. Three of the four cameras above use a gap-less microlens to better focus light into the pixel (especially light that isn't coming straight-on). The 500D is the only one that doesn't. So while the 500D is less dense when compared to the 550D, the 550D can actually render slightly less noise than the 500D, in spite of the pixel density, and it's due to the microlenses effectively increasing the size of the bucket just a little.

Okay -- so real cameras aside, let's imagine a full-frame sensor and a crop sensor that has the same megapixels per square centimeter. Let's imagine that those pixels are made the same way. Let's imagine that they both have gapless microlenses, and on-and-on.

At that point, the FF will have more pixels on the sensor, and so will render a wider field of view. But it's also catching the parts of the lens that aren't as good as the center, and so IQ will deteriorate at the edges.

The crop sensor has fewer pixels, and will render a smaller field of view. It is capturing only the better parts of the lens, so the IQ will be more consistent across the frame.

But, if you took the image from this imaginary FF sensor, cropped the center to the same FOV as the crop sensor, lo-and-behold, the cropped image from the FF sensor will be exactly the same as the image from the crop sensor. (And I mean exactly: depth-of-field and all.)

So in the real world, the better image quality afforded by the 5Dmk2 is because the pixels are larger. Which means less noise, and better high-ISO capability. The 550D, while it could theoretically capture more detail, loses some of that detail to the extra noise induced from cramming so many pixels in one spot. It also loses detail from the lens -- where the lens may simply be unable to resolve completely to one pixel. And it can't perform at high-ISO as well.

So, if we take the same image on the 5dmk2 and on the 550D, and then crop the 5Dmk2's image to the same crop as the 550D, the images will not be 100% identical. The 5Dmk2 will retain better IQ over-all (less noise, etc.), but the 550D could theoretically retain better detail over-all at the expense of being noisier than its bigger brother. (Whether or not the noise would overcome the detail would depend on a lot of things, and I don't have a 550D and a 5Dmk2 to verify which one wins.)

Does that help? Or did I just make things more confusing?

rickp

No that was good. I understand the design differences and how one affects the.
At least now I can follow what I'm reading a bit better.

Thank you for your time.

R.