Would someone explain the physics of this to me. Are these pixels in anyway compromised when compared to the 8.2 I have on my 30D?. I thought that when you increased MPs on a small sensor there was a degradation of IQ
For the same sensor technology, you are correct. However, the 50D has gapless microlenses and larger photosites per pixel, which means that they actually are larger pixels per pixel pitch, and may even be larger pixels than the 40Ds in terms of actual area that gathers light.
That coupled with the new Digic4 and advances in CMOS technology add up to what is supposed to be a 1 to 1.5 stop advantage in noise, even WITH the added 5 MP. So ISO 6400 on the 50D will be BETTER than ISO 3200 on the 40D. Just think how clean the 7.1 MP sRAW files at ISO 6400 will be, with 2 to 1 pixel binning.
No sensors are completely different. Especially the microlenses which are now gapless. Also the per-pixel-noise reduction has improved by treatment through DIGIC IV. It's just 'urban legend' that more MP decreases IQ. Technology improves and Canon pushed the envelope once again for the sake of EOSfun!
I think they are venturing into charted territory where you place too many megapixels on the sensor and start to loose IQ. Remember the old prosumer cameras like the Minolta A2. I can't remember the pixel count but developers started seeing distortion on the fringes when they went past a certain pixel count on the sensor (5.6mp maybe).
I'm really surprised at Canon's announcement of the 50D and honestly expected a new 5D to be announced instead. I hope this isn't a sign of a new megapixel war between manufacturers.
Might be a bit too much to explain in a forum John.
Anytime I start pondering the technology, I revert back to thinking about computer processors. They were the same physical size several years ago as the chips of today, but the new ones only perform about 15000 times better.
I know it's not apples to apples, but if there was some form of significant compromise I don't think we'd been seeing the MP push of the past few years. Frankly, if the results are there, why do we even need to understand it?
Good picture Andreas, it is really worth a 1000 words
Basically as long as the photosite size remains the same, all other things being equal, the SNR remains the same. BUT, all other things are NOT the same, i.e. the new DIGIC-IV etc. and the SNR may actually be better on the 50D.
I'm gonna ask a silly question but on the diagram of the 50D sensor, where is the coverage on the outer edges of the sensor coming from? Are there paritial diodes on the edges?
And how does the diode design (gapless vs. gap) change the fact that you still only have a limited amount of surface area?
It doesn't change the fact...it just means you can fit more of the same sized pixels on the same wafer (i.e. pixel number increase without making the pixels smaller).
Diffraction will kick in at about f 8 with this pixel density, that means stopping down to f 16 for depth of field is useless. Also this sensor will outresolve a lot of lenses. I am not happy with this pixel race at all, I hope the 5DII if it ever comes will not have more than 16mp.
By removing the earlier microlens gap itīs now possible to have more photosites in same area with the same signal-to-noise ratio. If also the microlens is redesigned to put light to the complete area of the photodiode then the signal-to-noise ratio is improved..
coppertop wrote:
I think they are venturing into charted territory where you place too many megapixels on the sensor and start to loose IQ. Remember the old prosumer cameras like the Minolta A2. I can't remember the pixel count but developers started seeing distortion on the fringes when they went past a certain pixel count on the sensor (5.6mp maybe).
I'm really surprised at Canon's announcement of the 50D and honestly expected a new 5D to be announced instead. I hope this isn't a sign of a new megapixel war between manufacturers.
the pentax k20d has a 14.6mp sensor in the mid price range and at the lower end of the market, the sony a350 weighs in at 14.2mp: so like it or not the age of the mid-teen mp cropped sensor camera is already here. the variable is that some manufacturers will execute better than others.
as for a 5d replacement, as others have reminded people canon has at least once in the past 4 years, made two announcements before photokina: the 20d and the 1ds2 were announced separately and about 2-3 weeks apart. it seemed that that year canon felt it had two landmark cameras( and it did) and elected to introduce them separately: perhaps they have that feeling again.
Geert Koning wrote:
Diffraction will kick in at about f 8 with this pixel density, that means stopping down to f 16 for depth of field is useless. Also this sensor will outresolve a lot of lenses. I am not happy with this pixel race at all, I hope the 5DII if it ever comes will not have more than 16mp.
Gosh, this misconception about pixel density and diffraction has to STOP.
Optical diffraction happens at the aperture blades on the LENS. As the aperture is made small, the wave nature of light becomes important and geometrical optics starts to break down.
Having greater pixel density does NOT make diffraction any worse. It merely shows the effects more clearly, the same way that optical qualities of poor cheap lenses are made more obvious. If you do not want to see effects of diffraction, you can either downsize your images or STOP pixel peeping. Landscape photographers will tell you the effects of diffraction are often overblown.
BTW, the 5D replacement will have 21 MP and video recording (which you'll see on Nikon D90). This has been leaked by someone called dHitman in DPReview. He correctly leaked the availability of 18-200 and 50D even as people ridiculed him.
Another misconception. There is no outresolve. A better sensor will always make better resolution with every lens, just like a better lens will add resolution to a sensor than a bad lens. Have EOSfun!
WE have to wait the first TESTS!!! IF the reviews are in favor of 50D,I'LL SELL MY 2 BODIES OF 30D and buy 2 of 50D.(I ALWAIS TAKE 2-BECAUSE YOU NEVER KNOW WHAT CAN HAPEND)
Geert Koning wrote:
There is more to it than only SNR
Diffraction will kick in at about f 8 with this pixel density, that means stopping down to f 16 for depth of field is useless. Also this sensor will outresolve a lot of lenses.
A couple of misconceptions here. First off, diffraction has nothing to do with pixel count. It is a function of the lens, and all lenses have it. The greater the resolution of the sensor the more visible the flaws of the lens will be. So, stopping down to f16 is not "useless", even if there is diffraction. Also, the sensor being able to "outresolve lenses" as you say, is not a bad thing. It just means the sensor is capable of taking advantage of even better lenses, and ultimately more detail.
Here's an example of diffraction:
Here's the scene I had to shoot, very high depth of field to keep the front corner of the couch all the way to the back wall in focus:
So I had to stop down to f18 to maintain DOF, but suffering from diffraction. But what if I shot at f11 to avoid diffraction? That's right, a portion of the scene becomes out of focus:
So is using f18 on my 1Ds3 "useless" because of diffraction? Of course not, as this example proves. Yes, all lenses (not sensors) suffer from diffraction at narrow apertures. Does this make them "useless" at narrow apertures? No. We shoot at the aperture required to produce the depth of field necessary to get the shot... Does this mean that we should avoid sensors with high resolving power so we don't see the flaws inherent in the designs of the lenses we choose? Of course not.
