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BMCC could be globally-shuttered with a rotary disc shutter (or LC shutter) add-on

handheld BMCC global shutter

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#1 TUG/BOAT

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Posted 28 November 2012 - 02:38 PM

I loathe the idea of buying a camera whose rolling shutter speed is not significantly faster than the 5D mark ii. The BMCC would be far more appealing to me if it had a global shutter.A rotary disc shutter add-on could do the trick.The sensor is small enough on the BMCC that an appropriate rotary disc shutter needn't be very large.15cm in diameter is probably overkill, but the bigger the better for the purposes of eliminating rolling shutter.It could have a male mFT mount on the camera side and a female canon EF mount on the lens side.The shutter angle should be variable as in the Photosonics and Hulcher 70mm cameras.There needs to be a syncing mechanism.It's complicated, but not ridiculously so.Blackmagic oughta whip something up in time for the wide release of the mFT-mount BMCC.I would pay $500 without a second thought.Matter of fact, any one of the 35mm-adapter companies could make themselves relevant again by making a universal e-mount/mFT rotary disc shutter. The spinner guys are already almost there. (Why the hell hasn't this happened already?)Thoughts?

#2 EOSHD

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Posted 28 November 2012 - 02:44 PM

This is an interesting idea. Possibly the challenges are that it is a very specialist piece of machinery to produce and you can't really find a third party supply for it? Also heavy on the battery and would be difficult to fit in the mount. F65 has rotary shutter but that is PL not EF / MFT.

I don't think they could do one for $500 either. This is a very high precision piece, it needs to be utterly perfect in manufacture for zero vibration and noise at such fast spin speeds.

#3 TUG/BOAT

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Posted 28 November 2012 - 05:52 PM

Well, nearly every film-based movie camera in existence uses a rotary disc shutter, and many are very quiet.

1440 rpm is what's required for 24fps. DVDs are read at 1530 rpm on the innermost edge, so every portable DVD player is capable of spinning a DVD at 1440 rpm, and most aren't very loud.

A non-uniform shutter disc spinning at 1440 rpm could introduce a slight 24hz shake. One answer would be to make the disc shutter a uniform clear disc painted black with the desired shutter angle.

The entire system could be engineered from standard DVD player parts.

A DVD-sized rotary disc shutter would even work decently with super35mm sensors.

#4 Mark Virtue

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Posted 28 November 2012 - 06:18 PM

How about an LCD shutter in front of the lens? I'd run across a web page of a company that builds them and has the sync box for it. The price was not cheap, around 2K USD.

EDIT:
Found the link http://tessive.com/

Edited by Mark Virtue, 28 November 2012 - 06:35 PM.


#5 galenb

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Posted 28 November 2012 - 08:17 PM

Um, Maybe I'm misunderstanding you? It seems like you are suggesting that by attaching a rotary shutter it will somehow enable global shutter on the camera? As far as I know, the sensor has to be made to support global shutter in the first place. And, even if it did, it would need to be switched on in software before it could even be utilized. So we are also talking about hacking the firmware. And, there is a tradeoff with global shutter too. Loss of dynamic range so I would expect that we would loose the 13 stops of latitude in the process.

Am I missing something?
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#6 TUG/BOAT

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Posted 28 November 2012 - 08:48 PM

How about an LCD shutter in front of the lens? I'd run across a web page of a company that builds them and has the sync box for it. The price was not cheap, around 2K USD.

EDIT:
Found the link http://tessive.com/


Good find.

This should do the trick, but they say it needs genlock for sync. And you lose a stop. And it's 2 grand...

#7 Mark Virtue

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Posted 28 November 2012 - 08:56 PM

HD-SDI passes the genlock, assuming I am reading web pages properly.

#8 TUG/BOAT

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Posted 28 November 2012 - 09:50 PM

Um, Maybe I'm misunderstanding you? It seems like you are suggesting that by attaching a rotary shutter it will somehow enable global shutter on the camera? As far as I know, the sensor has to be made to support global shutter in the first place. And, even if it did, it would need to be switched on in software before it could even be utilized. So we are also talking about hacking the firmware. And, there is a tradeoff with global shutter too. Loss of dynamic range so I would expect that we would loose the 13 stops of latitude in the process.

Am I missing something?


Yes, you are missing everything.

Imagine a rolling shutter cmos sensor shooting at 24fps and using a 1/24s shutter.
Each pixel is read, reset, and immediately begins integrating again.
The rolling shutter takes a certain amount of time to read/reset the first pixel to the last.
Every camera is different.
The 5dmkii takes 1/40s (25ms) to read/reset it's sensor. This means there is a period of time in which all pixels are simultaneously integrating which is: 1/24s-1/40s=1/60s

(1/60)/(1/24)=0.4

40% of 360degrees=144degrees

So the 5dmkii can have up to a 144 degree shutter and be just as globally shuttered as a film camera.

But not even a rotary shuttered film camera is truly globally shuttered, given that it takes time for the shutter edge to pass over the sensor. So, the shutter should be sufficiently large in diameter that it doesn't take too long to occlude the sensor.

I don't know how the 5dmkii's 25ms rolling shutter read/reset speed compares to the BMCC, but from what I've seen they appear roughly similar.

#9 galenb

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Posted 29 November 2012 - 05:43 AM

Um... I understand the difference between global and rolling shutter. But I think you are missing my point which is that sensors need to be made to support global shutter as an acquisition method. Maybe you know something that I don't but as far as I knew, the sensor on the BMCC is not a global shutter sensor. So, you can't simply glue a rotary shutter onto a digital camera and expect it to produce global shutter.

#10 hmcindie

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Posted 29 November 2012 - 09:24 AM

No. The rotary shutter would be in sync with the rolling shutter of the cmos and thus provide a global shutter. Like in the F65. This is completely different than designing a global shutter cmos (like in the F55).

#11 TUG/BOAT

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Posted 29 November 2012 - 02:14 PM

HD-SDI passes the genlock, assuming I am reading web pages properly.


It looks like a pretty good product. It has come down in price, too. The price was around $14,000 less than a year ago.

Now its $2k... Practically reasonable...

#12 TUG/BOAT

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Posted 29 November 2012 - 02:38 PM

Um... I understand the difference between global and rolling shutter.

I'll take your word for it.

But I think you are missing my point which is that sensors need to be made to support global shutter as an acquisition method.

Nonsense.

Maybe you know something that I don't but as far as I knew, the sensor on the BMCC is not a global shutter sensor.

Actually, if it uses the Fairchild CIS 2051 sensor like many think it does, then yes, it can be read either rolling or globally, but that's beside the point, as we're talking about mechanically globally shuttering the sensor while it reads in rolling mode

So, you can't simply glue a rotary shutter onto a digital camera and expect it to produce global shutter.

With proper sync, yes you can.

But hey, maybe an lcd shutter beats a rotary disc for noise, and bulk. The Tessive is now $2,000 and for most cameras can do the job...

If I was more of an electrical engineer, I'd repurpose a pair of active shutter lcd glasses like this guy:

Dan Hudgins has made many insightful posts about this topic and I'd be curious to hear his thoughts.

#13 galenb

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Posted 29 November 2012 - 03:18 PM

Well then, I guess I don't understand.





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