I Thought I Understood Camera Shutters And Flash Until I Saw This

I thought I knew everything about shutters, sync speeds, and flash duration until I saw this video by Paul Duncan. I smugly started playing this recommended video and I got schooled. Now I am up to speed and you will be too.


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25 Comments

Does anyone here know more about the electronic shutter and why camera companies don't use it with Cmos sensors? I remember reading it was only used with CCD. Surely we could go back to that method with CMOS or maybe now CCD technology is better to where we can get improved image quality AND high speed sync.

Lee Morris's picture

@Jerry, I have wondered the exact same thing. I'm not even sure if the cameras need mirrors anymore. They could create a camera with a super HD digital viewfinder and there would be no shutter delay, noise, or syncing issues. Maybe one day.

@Lee: Without a mirror, no fast phase detection AF is possible.

Thanks for this video, it was really informative!

Hey, that really is a good tutorial video!

@Lee The camera you described already exists as a HDSLR -- the Sony a55 and a33 bothe use a beam splitter to have simultaneous images on the viewfinder and on the sensor. The compromise is that the viewfinder is electronic, not optical. I don't know if that would bother you, but it would bother me.

Lee Morris's picture

@Brian, very interesting! Now if we can just get a real camera manufacturer to make one... I kid!

Thanks for this video. Posting it to my blog for sure. I always wondered about 2nd curtain flash. Very cool!

I am still partial to the way my D70's sensor works - unlimited sync. The curtain's maximum speed is 1/250 and everything after that is electronic shutter via the nature of interline CCD's. However, there is a -huge- penalty for it: the rows on the CCD alternate capture rows and data saving rows, so the 6mp camera actually has 12mp worth of dots - small dots leads to high noise. In traditional CCD sensors, you have a row on the edge that sends the data back, one captured row at a time, so if you have a few thousand dots worth of data, it needs to be done in darkness.

...long story shot, it's all about sensor design: you want maximum area for capturing elements (pixels) else you have bad noise.

MK is right about AF, you need a mirror, or a beam-splitter like Sony has done, which has inherent light loss.

But I do really wonder why CMOS sensors haven't been used for electronic shutters. They're certainly capable of it, since that's what you're doing when you use DSLR video, which can do high shutter speeds.

your DSLR video uses a rolling electronic shutter that functions similarly to the DSLR's mechanical shutter, it does not record the entire frame at the same time like the D70's Global shutter system, but rolls through the sensor vertically. which is why there can be motion artifacts when panning a CMOS DSLR or camcorder. it has to do with the actual electrical engineering of the CMOS sensors, currently no CMOS cameras or camcorders have global shutters, but i expect that we will see an improvement to this very soon.

I think there are two reasons we don't get a lot of these nifty features and they both have to do with sales.
The first one is that camera companies need to maintain their long-term income. In many cases this means not introducing every new feature they can at once so that they can keep introducing new models and new technologies to keep you upgrading.
The second reason I think has more to do with our habits and fear of the unknown. It would be weird if Canon suddenly released some new super-camera that had hundreds of new features you hadn't heard of and cost 100,000$. It wouldn't sell well because people wouldn't know what to think about it and it would cost too much.

Talking about strobes... What do you guys suggest for AA batteries?

Patrick Hall's picture

Click on the gear guide we have up on the right hand side...then goto accessories maybe

does that guy know how to party or what! :) that was really well explained, good vid! I'm desperate to do high speed sync but with my large lights, i can squeeze 320th of a sec out ok on my d300 with my abr800 and cheapo interfits, but i really wanna go just a bit faster as i can still see some blur :( maybe some DIY trigger mod to fire one flash fraction of a second after the first... anyone seen anything like that? so lee you guys not gonna be interested in the Sony E NXCAM range? :P

Excellent - thanks for this

Great video, Paul Duncan is a great teacher.

One last resort technique for higher shutter speed is simply to frame larger, and then crop out the black bar.

The reason they dont use electronic shutters with CMOS sensors is because of rolling shutter. Cell phone camera use electronic shutters and have obvious rolling shutter.

The reason most modern cameras with APS-C or larger sensors don't use electronic shutters is as Kyle described. It requires one shielded pixel area for data storage for each pixel. When the first curtain has cleared the sensor, it zeroes all of the photosites. After they are cleared, charge builds up in them again because they are still being exposed to light. When the proper amount of time has elapsed, every shielded pixel reads from its unshielded counterpart and stores the value it finds. The camera only reads from the shielded storage areas. It's like a buffer built into the sensor.

This makes each individual pixel smaller, which means less thermal inertia and more noise at high simulated ISO speeds (actually, the 'ISO' rating at which you are shooting is the level of amplification applied to the data as it is read). It also means impractically low pixel counts for an industry where the majority of consumers don't care about subtle features like this. Many people just pick the camera with the bigger number, just like the gigahertz war in computer processors.

Newer photolithography techniques may allow for multi-layer sensors to be constructed (kind of like a Foveon sensor) with the shielded buffer pixels beneath the unshielded active pixels. This would likely be prohibitively expensive right now, but it is a logical future step for professional-level full-frame DSLR sensors.

A very helpful, clear and concise explanation Paul.. many thanks

I got lost in between 2:49 and 4:20.

1/250 and 1/125 sec. Ah I got those =)

t.5 t.1 huh? Aren't those the Terminator models?

Oustanding tutorial! I've been using second curtain flash on my Olympus e-10 and Nikon d70s for years. Until now, I never fully understood why they look so nice. Thank you for the great information and clarity.

Great video. Very informative. Well done.

This was very informative. The only other thing I didn't come up with on higher sync speeds is just cropping out the black bar: Like this http://www.youtube.com/watch?v=JNYUXmN_wcQ

Brilliant!