Add physical shutter to 5D2 to eliminate wobble, Dan Vance style?

P

PaulM

Member
How about putting a physical shutter of some kind in front of the lens mount on the 5D2 to block light from the CMOS sensor during the read/reset phase of sensor readout?

Dan Vance knows all about this stuff: VanceCam VC25P Camcorder

According to the FAQs on the website of a company that makes Liquid crystal shutters, LCD Shutters from Liquid Crystal Technologies. Our liquid crystal shutters can solve many different design challenges., LCD shutters are less than ideal for cameras.

Seems like a half-disc spinning at 1800 RPM in sync with the camera's pulses is the way to go.

Using medium format lenses with long focal flanges would allow for the added bulk between the lens and the 5D2; the Mamiya RB67 flange focal distance is 112mm.

180 degree shutter and few/no rolling shutter artifacts would be nice.

Sounds plausible, no?
 
Here's how I think it would work:

1. Lock 5D2 at 1/30th shutter. (This isn't very straightforward but it can be done)

2. Spin, at 1800 RPM, as large a half-disc as is practical in front of the lens mount, in sync with the 5D2. Syncing may be difficult (http://www.theshiveringearth.com/VC25PTechTSE.htm ), but in the end you'll have a working shutter speed of 1/60th as the half-disc will be obstructing the sensor 50% of the time. During this period of obstruction, the sensor will be reading and resetting each pixel in a rolling fashion, but because of the mechanical shutter, the read/reset phase will take place in darkness. Therefore, no new light will be hitting the last-to-be-read pixels on the sensor after the first-to-be-read pixels have already been read and reset.

3. Mount Hasselblad or other medium format lens at the appropriate distance from the 5D2 sensor, with the spinning shutter between.
 
This arrangement would still suffer from rolling shutter artifacts, but they would be more akin to the rolling shutter artifacts of 35mm motion picture film cameras than CMOS video cameras, I believe.

Should work for the Red, too.

No?
 
PaulM said:
During this period of obstruction, the sensor will be reading and resetting each pixel in a rolling fashion, but because of the mechanical shutter, the read/reset phase will take place in darkness. Therefore, no new light will be hitting the last-to-be-read pixels on the sensor after the first-to-be-read pixels have already been read and reset.
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How will this help ?

The problem is the temporal divide between the top and bottom of each frame.

This is what causes skew and wobble (and all rolling shutter jelly fun).

How will your idea help this ?
 
Lee Wilson said:
How will this help ?

The problem is the temporal divide between the top and bottom of each frame.

This is what causes skew and wobble (and all rolling shutter jelly fun).

How will your idea help this ?
Click to expand...

The camera would work like a DSLR in a serial frame shooting mode. The sensor would be exposed all at once and after that, when the shutter is closed, the readout would start - no skew at all. But I suppose there has to be some sync with the life view mode to make it work. (and no 360 degree shutter or there would be no time left for the readout, I suppose)


Lee Wilson said:
:zombie_smiley::crybaby::zombie_smiley::crybaby:
Click to expand...

hahaha... :Drogar-Love(DBG):
 
joe 1008 said:
The camera would work like a DSLR in a serial frame shooting mode. The sensor would be exposed all at once and after that, when the shutter is closed, the readout would start - no skew at all.
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!!

Are you suggesting getting rid of the CMOS sensor and replacing it with a global shutter sensor (like a CCD) ?
 
Lee Wilson said:
!!

Are you suggesting getting rid of the CMOS sensor and replacing it with a global shutter sensor (like a CCD) ?
Click to expand...

Of course not.

I just got an email from Dan Vance.

He had the good idea of proving the concept by first using a liquid crystal shutter, as they are much easier to sync.

He did this himself with another camera, using the LC shutter from a pair of $15 3D shutter glasses.

I think I might give it a shot.
 
joe 1008 said:
The camera would work like a DSLR in a serial frame shooting mode. The sensor would be exposed all at once and after that, when the shutter is closed, the readout would start - no skew at all. But I suppose there has to be some sync with the life view mode to make it work. (and no 360 degree shutter or there would be no time left for the readout, I suppose)
Click to expand...

Is Joe the only one who gets me?

Are you other guys trying to troll?

I didn't come to these boards looking for bad jokes. I came for help with a technical idea that might improve the function of a great camera.

I love my 5D Mark II, but I hate its wobble.

I'd like to be able to shoot handheld. Right now, I pretty much can't.

The shutter on an Eyemo film camera is a spinning half disc; the camera doesn't have a reflex viewfinder.

The discussion here ( http://www.reduser.net/forum/archive/index.php/t-15436.html ) is about the possibility of a mechanical shutter for Red. In the last post Davide says:


With the Global shutter you set all pixels to gather charge then open the mechanical shutter, hold open for a while, then close the mechanical shutter, then start the "rolling" readout. Since the mechanical shutter is closed during the readout there is no visible rolling shutter artifact.

The artifact from the mechanical shutter depends on its radius just like in a movie camera like the Mitchell NC has a larger radius than an Eyemo. You can use two counter rotating shutters to get a faster open and close time.


This is an important point about the radius of the mechanical shutter. The larger it is, the less time there is between the moment the sensor starts to become obstructed by the spinning shutter and the moment the sensor is fully obstructed.

If this shutter transit time is shorter than the time it takes to read the sensor normally, then, properly synced, the resultant footage would suffer from fewer rolling shutter artifacts.

Un-synced flashes would still be a problem, as they are with 35mm film cameras, but I can't remember ever seeing wobble at the movies.
 
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Karsvall said:
And then we have our NEW adapter.

Red Rock and the others are back in business again :-)
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Great idea Karsvall!

I'm going to shoot emails off to all those great businesses--Redrock, Brevis, Wayne Kinney--who could certainly produce some excellent shutter adapters, so long as the idea actually works...

Wobble the primary flaw holding the 5D2 back from being a true digital cinema monster.

The D90 might be helped, too...
 
That spinning shutter could be a fabolous idear for somebody who badly needs a 5D for handheld shooting.

I personally want to keep things simple. I consider the 5D the best available "brain" at this moment. I will adapt to its defects and will try to shoot good footage. When the next generation comes out, probably with much less artefacts, including wobble, I will move up the stairway to perfection. I will sell my 5D for a good price and maybe loose 1000$ for 6 or 8 month of shooting. (I suppose 2009 will be a great year for hybrid DSLRs)

I can keep the lens, the tripode, audio recording, rods, follow focus, mattebox - everything else. So the 5D in fact is a Canon-"brain". Specs will change, count on it! :Drogar-Evil(DBG):
 
PaulM said:
Is Joe the only one who gets me?

Are you other guys trying to troll?
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Not at all, I genuinely am a little confused by what is is you are suggesting, that is all.

The 5D has a CMOS sensor, so regardless of what goes in front of it - it's temporal view of the outside world will always have a vertical offset from the top to the bottom of the sensor.

PaulM said:
With the Global shutter you set all pixels to gather charge then open the mechanical shutter, hold open for a while, then close the mechanical shutter, then start the "rolling" readout. Since the mechanical shutter is closed during the readout there is no visible rolling shutter artifact.
Click to expand...

This is not applicable to the 5D2 as it does not have a global shutter.
 
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joe 1008 said:
I personally want to keep things simple. I consider the 5D the best available "brain" at this moment. I will adapt to its defects and will try to shoot good footage. When the next generation comes out, probably with much less artefacts, including wobble, I will move up the stairway to perfection. I will sell my 5D for a good price and maybe loose 1000$ for 6 or 8 month of shooting. (I suppose 2009 will be a great year for hybrid DSLRs)
Click to expand...


Exactly my own thinking.
 
Here's, more or less, the email I just sent to Zacuto, Redrock, Brevis, Cinemek, and Shoot35:

I have followed the 35mm adapter revolution since Agus Casse first posted some grabs on DVinfo.net. I instantly knew that DoF control was what I was needed for my digital filmmaking.

I tried making some adapters myself but was never satisfied. About a year ago I realized that the new generation of DSLRs with Live View meant that pretty soon full-frame and APS-C cameras would soon be shooting video.

Sure enough, the D90 and 5D2 are now here, but they both suffer from wobble due to the rolling shutter readout of their CMOS sensors. I have a 5D2 and it's incredible, but it pretty much can't be handheld at 50mm and up. Here and here I posted the idea of putting a mechanical shutter between the 5D2 and a medium format lens (to allow for the space required for the added shutter), to block light from the sensor during sensor readout. Non-reflex film cameras like the Eyemo work this way.

A spinning half-disc synced to the camera's pulses might do the trick. There are also liquid crystal shutters, but they aren't fully transmissive nor fully opaque.

If you guys built such a "shutter adapter" that actually prevented wobble, you'd have plenty of customers: 5D2 customers, Red One customers, and certainly D90 customers, if it was inexpensive enough.

A spinning shutter would also still cause rolling shutter artifacts, but they would be like the RS artifacts we see in movies shot on Arris, for example. So long as the diameter of the spinning disc was big enough, the transit time of the leading edge of the disc would be faster than the readout transit time of the sensor, thus reducing RS artifacts, especially wobble.

Jim Jannard was just saying that the RS artifacts we're used to seeing in movies shot on film cameras make the image more dynamic. I don't agree, but hey, if a spinning shutter adapter could make a video camera look even more like an Arri, by replacing nasty wobble artifacts with more subtle RS artifacts that were used to seeing in 35mm films, I'm sure it would be welcomed.

I know that if it can be done, you're the guys to do it.

The hybrid DSLR/videocamera isn't going away. Unfortunately, rolling shutter CMOS readout probably isn't going to be replaced by global readout any time soon.

That's where you guys come in!

Thanks for taking the time to read this.

I look forward to any correspondence.

 
Lee Wilson said:
Paul.

Can we agree that the 5D2 has a CMOS shutter ?
Click to expand...


The 5D2 has a CMOS sensor. Some CMOS sensors can be read in a rolling fashion, others globally.

The 5D2 CMOS sensor is read in a rolling fashion; it has a rolling shutter.

However, if one can obstruct the path of light to the sensor during the rolling readout, the readout will occur in darkness. Therefore, over the course of the readout, no new light will be integrating at the bottom of the sensor while the top is being read.

Wobble occurs when light hits the bottom of the sensor after the top of the sensor has already been read and reset, but the bottom of the sensor hasn't yet, because of the time it takes for the rolling shutter to read and reset the sensor, from top to bottom.

I'm pulling this number out of my ass, but let's say it takes the sensor 5 milliseconds to read/reset itself, from top to bottom. To reduce rolling shutter artifacts, one would need a spinning half-disc large enough in diameter that when spinning at a rate of 24 or 30 revolutions per second (to match the camera's framerate), the leading edge of the half-disc would have to take less than 5 milliseconds to cover the sensor. The larger the diameter of the disc, the faster the shutter leading-edge transit time. This transit time would then serve as the new functional sensor readout time, because once the sensor is in darkness, it doesn't matter that readout occurs in a rolling fashion because the pixel values aren't being altered by new incoming light during readout.

M'kaaay?
 
PaulM said:
The 5D2 has a CMOS sensor.
Click to expand...

Whoops! Sorry, yes that is what I meant.

PaulM said:
However, if one can obstruct the path of light to the sensor during the rolling readout, the readout will occur in darkness. Therefore, over the course of the readout, no new light will be integrating at the bottom of the sensor while the top is being read.
Click to expand...


But the light (the charge) that is being converted to a digital value will still have a temporal offset (from the top to the bottom of the sensor) regardless of what happens during the readout.
 
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