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Why doesn't Nikon use electronic/hybrid shutters on *all* of their DSLRs?

Epp B , Mar 29, 2009; 07:04 p.m.

Does the shutter curtain in a digital SLR serve any purpose other than a bit of physical protection for the sensor?

I suspect the answer is "no" (correct me if I'm wrong), which got me wondering: if Nikon can x-sync the D40 (and a few other older DSLRs) up to 1/500 because of the hybrid shutter...

Why not implement this across their range of DSLRs?
Shoot, even the D3 can't sync that high! Sure, if you can afford a D3, you can afford lighting with enough power, but who'd say no to faster recharge times?

What's holding Nikon back from syncing hyrbid shutters up to the maximum?
If I tape over the TTL contacts on the hotshoe, I can x-sync my D40 all the way up to 1/4000! Of course, I lose TTL flash metering, but this is irrelevant when I'm bouncing the flash, anyway (which is what I'm doing most of the time).

Responses

Joseph Braun , Mar 29, 2009; 07:28 p.m.

ironically the cheaper shutters sync faster.. go figure.

Walt Flanagan , Mar 29, 2009; 08:22 p.m.

Read the section on CCD architecture concerning frame transfer vs interline sensors. I know this is about CCD, I don't know how much applies to CMOS, but the D100/D70/D50/D40 which had the 1/500th flash sync all used a very similar 6MP CCD.
http://en.wikipedia.org/wiki/Charge-coupled_device#Architecture

Joseph Wisniewski , Mar 29, 2009; 08:35 p.m.

Since you asked "why not" and "what's holding Nikon back"...

An electronic shutter requires the sensor to be equipped with what is commonly called "snap shutter" circuitry. Basically, this is a second set of diodes, as big as the light gathering photodiodes, but shielded under a dark cover, and some additional switches. To shoot, the photodiodes are cleared of charge, exposure starts, and at the end of exposure, the charge in the diodes is transferred over to the shielded storage part of the cell. The cell is already full of stuff, so the only way to make space for this extra circuitry is to cut the size of the photodiode in half. Which cuts dynamic range and low light, high ISO performance.

A second problem is that with a full mechanical shutter, photodiodes are in the dark most of the time and only exposed to light during the actual exposure, so protecting the sensor from overloads (which cause charge to "spill" across the chip and create lines or blobs of light) is fairly easy. But look at that D40 you mentioned. The mechanical shutter is slow, 1/90 sec to open or close. So for a 1/2000 sec "sunny day fast lens" exposure, the chip is blasted with light for a full 1/90 sec while the shutter gets opened, 22 times as much light as hits it during the actual exposure. That means blooming is 22 times harder to control. I had a D70 for a short while, and like the D40, you saw a lot of blooming. Sunsets were a disaster, interior architecture had streaks coming off light fixtures, etc.

Joseph Braun mentioned that the cheaper shutters sync faster. That's why, because in the cameras that had actual 1/90 sec sync, Nikon made the decision to give up dynamic range and increase blooming to raise sync to 1/500 sec. That's why the last pro bodies with electronic shutter were 8 years ago, Nikon D1 and Canon 1D.

Epp B , Mar 29, 2009; 08:59 p.m.

Wow, great explanation! That answers both of my questions perfectly.

So, are CCD sensors behind fully-mechanical shutters less prone to blooming then?

Scott Pogorelc , Mar 30, 2009; 12:36 a.m.

Joseph, you are a technical stud. I love reading your answers.

Pete S. , Mar 30, 2009; 08:21 a.m.

To have an electronic shutter requires more electronics on the sensor and that means less light sensitive surface area, commonly called fill factor. Since the photosites are effectivly smaller, more noise and less dynamic range is the result. So if Nikon wanted to have an electronic shutter they would have to sacrifice dynamic range and low noise. Most customers prefers low noise so that is reason number one.

Reason number two is that only CCD technology is really used for electronic shutters and CMOS technology is cheaper to manufacture, have lower power consumption and in the DSLR application gives lower noise. Blooming is a CCD problem but it can be solved with the design (for instance using anti-blooming gates) so that is not really an issue. CMOS censors can also be manufactured with the extra electronics required to have an electronic shutter but the problem is still that sensor surface area needs to be sacrificed.

So Id' say the reason why Nikon isn't using electronic shutters is for low noise and economics. Maybe they are able to combine the electronic shutter with low noise on a CMOS sensor in a few years.

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