Difference in CCD and CMOS?

[durr3]

What are the advantages and disadvantages of the CCD and the CMOS chips? Thanks

[bobatkins]

There are none. It doesn't matter (at least as far as the user is concerned).

[durr3]

Thanks Bob.

[frank_skomial]

The CCD shutter in Nikon D70 allows single flash shot synchronization at all electronic shutter speeds down to 1/8000 of second.

 

There is no equvalent capability in currently implemented cameras with CMOS sensors.

 

If you do not intend to use flash outdoors, then the difference perhaps would not matter to you.

[bobatkins]

Maximum sync speed on the D70 is given at 1/500s in the Nikon specs.

[briany]

Yeah, Bob, but it's widely known to be possible to sync above that. Given the limitations, I think it's mostly academic.<br>

<a href="http://www.kenrockwell.com/tech/syncspeed.htm">http://www.kenrockwell.com/tech/syncspeed.htm</a><br>

<a href="http://wetpixel.com/forums/index.php?showtopic=6169">http://wetpixel.com/forums/index.php?showtopic=6169</a><br>

<a href="http://www.bythom.com/D70REVIEW.HTM">http://www.bythom.com/D70REVIEW.HTM</a><br>

<br>

Durr, the differences, as stated, aren't too meaningful for the average user. This site is interesting, from a manufacturer who manufacturers both CCD and CMOS:<br>

<a href="http://www.dalsa.com/markets/ccd_vs_cmos.asp">http://www.dalsa.com/markets/ccd_vs_cmos.asp</a><br>

and you can read all the links on the right hand side, the most recent of which is the 2005 update, <a href="http://www.dalsa.com/shared/content/pdfs/CCD_vs_CMOS_Litwiller_2005.pdf">http://www.dalsa.com/shared/content/pdfs/CCD_vs_CMOS_Litwiller_2005.pdf</a>

[frank_skomial]

The D70 flash sync at speeds even higher than 1/500 is fully usable. It allows unprecendented flexibility and creativity with flash photography indoor or outdoor.

 

E.g. you can achieve very narrow DOF in broad sunny day (the best effect photographers are after when doing outdoor portraits), you can change daylight lighting into a nightly looking scene, you can freeze extremely fast moving objects, you can experiment obtainig other flash effects not availabe with regular CMOS shutter (perhaps more into scientific usage ?)... just to mention few.

 

The best lens to use this technique is the Nikkor 85/1.4.

 

Bob, Nikon specs are sometimes proverbial "tip of the iceberg". One must try things to learn more.

[joshua daniels]

CCD or CMOS have nothing whatsoever to do with synch speed. As I understand it, it has to do with the way the dedicated flash and the focal plane shutter synchronize, so that the flash blasts multiple times at speeds above that at which the shuuter opens and closes fully. In effect, the high synch speeds involve flashing for each segment of the sensor that the shutter exposes (focal plane shutters expose a section at a time above the full open / close speeds).

[basscheffers]

Every sensor looks different, just like every type of film does. There is a distinct difference in look between different manufacturers and technologies. None of them are worse or better than the other, just different.

 

You choose a camera (partly) on the look you like. Well, you can, I doubt many people actually do.

[frank_skomial]

Josh,

 

It is quite contrary to what you say, clearly you do not understand.

 

"CCD or CMOS have nothing whatsoever to do with synch speed. As I understand it, it has to do with the way the dedicated flash and the focal plane shutter synchronize".

 

The fast single shot sync down to 1/8000 is only possible with the NON-DEDICATED flashes like Sunpak 555, Vivitar 283 and 285, and an older Metz that I tried.

 

With dedicated flash from Nikon, SB-800 (perhaps sb-600 the same), the D70 camera recognizes the Nikon flash and blocks usage of shutter faster than 1/500 (hence the advertised speed is only 1/500). With many non-Nikon brand flashes, the D70 logic does not prevent usage of the fast shutter for single shot synchronization.

 

The all speeds single blast flash sync (down to 1/8000) is the benefit of the CCD electronic shutter built into D70.

 

Purposely I say "single blast sync", to make distinction and not to get confused with the stroboscopic (multiplicity of blasts) High Speed sync FP (FP for Fast Pulse, Focal Plane, etc...) mode used on DX2 and other brand top level cameras, that is far inferior and limitted use technique.

[frank_skomial]

There is nothing wrong with not to understand something.

I do not understand many things. For example, I do not understant why Nikon advertized flash max sync speed at only 1/500 sec, while it could have gone much faster with the D70.

 

So, I guess, (I do not know), that there were reasons: (smile please).

 

1. Nikon sells all what they make, and could not afford the rush of requests for D70.

 

2. Nikon did not want to kill the competition right away, as they serve good market balance purpose, and drive the new product development and inventions.

 

3. Seriously... the speeds faster than 1/500 for Nikon brand iTTL flashes could possibly reduce reliability of the Creative Lighting System (CLS), when operating in multiple flash commander mode.

 

4. some unknown reaasons...

[jimstrutz]

Frank, my guess is that Nikon advertises 1/500 sync because most flash units take at least 1/1000 to dump a full load from their capacitors. Many of the big handle mount units, probably take a full 1/800 of a second at full power, making exposures unreliable at 1/1000 if you need full power. If they advertised 1/1000 and couldn't get common units to comply at full power some people would be irritated.

 

I don't have access to test it, but I suspect most Nikon's Speedlights can't get a full power pop into 1/2000. Few flash units can & most of those are the small suff. So while 1/8000 sync works, you will be limited in power/range. Not as much as the FP flash schemes, but still limited.

 

However, this is one situation that CCD's have shown a clear & compelling advantage over CMOS sensors if a manufacturer chooses to take advantage of the possibility. I have read that CMOS is not capable of doing this (fast electronic shutter), but technology marches on. Perhaps in the near future...

 

Anther difference in CCD & CMOS, is that CMOS theoretically takes less power to run, and therefore should run cooler, creating longer battery life and less digital noise in very long shutter speeds. Alas, I have not heard any CMOS users claiming their long star trail pics are so much longer and cleaner compared to their "old technology" CCD cameras. Mostly I hear, "I wish my new digital camera was as good at this as my old film camera."

 

I think the biggest advantage to CMOS is the lower cost of production. So far, that has mostly just advantaged the manufacturers. Still, one can hope for lower prices.

[joseph_wisniewski]

Joshua - "CCD or CMOS have nothing whatsoever to do with synch speed. As I understand it..."

 

CCD sensors can have an "electronic shutter" capability that CMOS sensors cannot have. Not all CCD sensors do have this, but the Nikon D70 and D50 (together accounting for the largest share of the CCD sensor DSLR market) do have it. That way, they just use the mechanical shutter of the dirt cheap Nikon N75 or N55 as a "light blind" (reducing smear and blooming) and use the electronic shutter to control the actual exposure. As Jim points out, Nikon protects for studio, heavy pro , and even some older Nikon on-camera flash units that need 1/800 sec for a full power flash. The Nikon can sync at much faster speeds,and it's fine at 1/1000 sec (even full power) with newer Nikon flashes (it would have been nice if the camera firmware knew this, though, so we didn't have to tape over the serial comunication contact on the flash to make 1/1000 sec (or above) work.

[joseph_wisniewski]

Durr - ignore people who post things like "There are none. It doesn't matter (at least as far as the user is concerned)."

 

Some of the major differences have already been covered, but I'll go over it all again, quickly, while adding some other advantages and disadvantages...

 

CMOS sensors can have very low leakage amplifiers on every cell, so they can run long exposures without building up leakage based noise or "bias" (an overall raising of level) in their pixels. This means CMOS sensors can do longer exposures than CCD sensors before you have to resort to techniques like "dark frame subtraction". Canon CMOS sensors (the biggest user of CMOS) are built this way.

 

CCD sensors can have electronic shutters. The high sync speed advantage has already ben covered. The electronic shutter also gives you a high top speed. Nikon D70 takes a cheap N75 1/2000 sec mechanical shutter and does 1/8000 sec with the electronic shutter. Electronic shutters don't have moving objects distorted in shape because of the moving "slit" of the mechanical shutter (remember the old racing pictures where wheels distorted into ellipses).

 

CMOS sensors are fully random access devices, while CCDs are serial devices. This means a CMOS sensor can access any cells on the chip, at random, at very high speeds. Let's pick on the Canon 20D sensor for a minute. It's an 8 megapixel sensor that can output 5 frames/sec for a total of 40 megapixels/sec. It's possible to only scan every fifth pixel, horizontally and vertically (there's a reason why you'd want to do every fifth one, but I won't get into it) so that you get a 320k pixel image at 125 (5x25) frames/sec, which means you can have a high speed electronic viewfinder. Canon tried this with their 20Da. This capability will be very important in the next couple of years...

 

CMOS sensor can be more integrated than CCD sensors. You can add circuitry that isn't "sensor" to the sensor chip, such as clocking and control (most CMOS sensors have this) or the A/D converters (very few CMOS sensors have this. Canon doesn't). This is an advantage for very small sensors, but on large sensors you'd end up paying more money (in reduced yields) to add stuff than you'd save vs. having a separate chip. It's great for "system on a chip" sensors for camera phones or security cameras.

 

Power, oddly enough, isn't a big difference. While a CMOS sensor typically uses about 1/10 the power of a CCD, it's just a drop in the bucket compared to what it takes to run a camera. A CCD may use 100mW (1/10 watt) for an APS sized sensor, but it takes several watts (display backlight, processor, DSP, memory, shutter motors, etc) to run a camera.

[mike_lepp1]

As a circuit designer I'm amazed when I read these. There is no difference between them to the consumer.

 

The most significant difference in design is you can buy an off the shelf ccd and do with it what you want. The cmos you need to do the design work at the sensor level to give it the feature you want. I don't think the consumer should care.

 

Beyond that, just about everything mentioned that pertains to consumer cameras can be worked around with specific engineering. CMOS can have excelent electronic shuttering, excellent image quality, and low noise (nobody mentioned that CMOS is inherantly noisier, this is because the circuitry is next to the cell causeing substrate noise). CCD can do long exposures, have blooming immunity, and have low power amplifiers (you can build low noise, low power amplifiers). With both you can only expose to when the cap (see below) is full. The smart way to do real long exposures is by doing a series of shorter ones.

 

The physics of the capture is identical. There's a photo cell and a mos cap in both of them.