Jump to content

Mechanical Shutter


Neil Duffy

Recommended Posts

You are half right. CMOS does "scan" the sensor instead of capture the scene at one instant. And there were skew issues with Peter Jackson footage shot on the 1st prototypes "Boris" and "Natasha" two years ago.

 

All CMOS are not the same. What matters is the read-reset time. The RED prototypes had a very slow (like most CMOS sensors) read-reset time (skew). We have been able to speed up that time dramatically since then. No one complains about the skew on the new firmware builds. They are now 3.5 times faster than they were. And the next generation, Scarlet and Epic, are even faster. About the same as a current film camera. Technically there is still skew in a film camera, just not enough to warrant a discussion. The N90 and 5D II have CMOS sensors that still have a very slow read-reset time... 3-4 times slower than a current RED ONE. That is why there is a LOT more skew when shooting motion with those two.

 

Read-reset times are independent of frame rates. Scanning a CMOS sensor is similar to a mechanical shutter "wiping" the film if the read-reset times are fast enough. Both of these have a "look" that is not the same as a global shutter. There is a "feel" to this wipe/scan time. Most people like it. Too slow read-reset time gives a bunch of skew... which is obviously not good.

 

The biggest problem with the discussion of CMOS sensors is that most people want to lump them all together. There are a million differences between them all, from pixel design, pixel size, A/D conversion, read-rest times, etc. Future discussions about CMOS will hopefully be more detailed, because the details matter. Sweeping generalizations don't work.

 

Jim

 

Jim, thanks for your very informative response. I confess, I have not seen footage from the latest builds. Also, I was confusing a mechanical shutter with a global shutter.

 

I saw skew and jello images as an issue on earlier builds, and was curious if there was an easy solution to this. The easiest solution appears to be to make the sensor scan even faster.

 

I think all cinema cameras are moving to the CMOS sensor. So a discussion of the different types and issues would be real welcome.

 

By the way, is this the first time that Jim and Keith agree on an issue related to RED? Maybe Phil will join them. :lol:

Link to comment
Share on other sites

I think all cinema cameras are moving to the CMOS sensor.

 

The gap between CCD and CMOS cameras is closing. However, using certain magic circuity external to the sensor, the CCD image should result in a higher image quality than CMOS, in many situations. The race towards CMOS is for a variety of reasons, and some of the early hype of 90's has been found to be incorrect. Moore's law does not hold really in its true sense in the image quality world. Economies of scale is not relevant in the typical sense here. Please see Wong's IEEE paper.

 

The key to a superb image quality is as much in the circuity surrounding the sensor, as the sensor itself, however, CMOS may not offer that luxury all of the times that a CCD does in many cases.

Link to comment
Share on other sites

Moore's law does not hold really in its true sense in the image quality world. Economies of scale is not relevant in the typical sense here.

Canon, Kodak, Sony, Fraunhofer etc. might disagree.

 

However everyone is entitled to an opinion which doesnt need to be based on facts.

Link to comment
Share on other sites

Canon, Kodak, Sony, Fraunhofer etc. might disagree.

 

However everyone is entitled to an opinion which doesnt need to be based on facts.

 

Von Krogh, you need to read carefully. I wrote "image quality" and not necessarily semi-conductor design of only the sensor chip. I am talking about full end-to-end image quality, which if you have been paying attention to my posts would have found out that I have repeatedly said that image quality is more than just sensor, where, unfortunately most discussion seems to focus solely upon, and rests on other stuff including but not limited to such things as electronic circuitry external to CCD/CMOS.

 

Have you ever personally investigated the results of even such stuff as where to put the ADC on an electronic circuit board to reduce the image noise (the sensor is not even the picture here in this case)?

Edited by DJ Joofa
Link to comment
Share on other sites

  • Premium Member
By the way, is this the first time that Jim and Keith agree on an issue related to RED? Maybe Phil will join them. :lol:

 

I rather suspect that for a sizeable percentage of questions about the RED, JJ and I would give much the same answer.

 

However, the laws of Physics prevent my total agreement with many of his statements.

Just as the laws of marketing prevent him from acknowledging the accuracy of many of mine (and Phil's) :rolleyes:

 

By the way, Keith is not writing this.

 

I'm actually just the guy with the Pooch-O-Matic mobile dog wash come to wash the dog. Keith let me use his computer to check my email, amd he left his c.com account open :lol:

Edited by Keith Walters
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...