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View Full Version : 24p omission explained



Terry_Lasater
05-28-2009, 02:28 PM
From Canon Rumors: link (http://www.canonrumors.com/2009/05/the-future-of-eos-hd-cr2/)

RichardVClark
05-28-2009, 03:17 PM
It sounds like what we all wanted to hear...That makes me skeptical

Robert Sanders
05-28-2009, 03:25 PM
Sounds like the 5D's CMOS chip was designed to be clocked at 60Hz. Hence the 30P frame rate. Which makes sense that you'd clock a "stills" camera at 60Hz or 120Hz rather than 48Hz or 96Hz.

They've probably had to write a 3:2 pulldown "hack" to make 24p work.

Pepster
05-28-2009, 03:35 PM
I don't get it. For any one wanting 24fps - just slow the camera's internal clock down, ie a hardware hack. I am a radio tech, and we have been doing this sort of thing for years.

If you slow the clock down, the camera will not know, and carry on blissfully unaware, just at a slower speed.

All of the 30fps - 25fps and 30fps - 24fps copnversions I have seen on VIMEO just look plain awful on pans when viewed on a 50" plasma TV - juddddder....

I do not understand what is holding back all thoes who live in 25fps land - just get in to it !

Robert Sanders
05-28-2009, 03:41 PM
It's not always that simple. I'm not an engineer and I suspect no one around here is either. However, I know enough to know that if the sensor was designed from the ground up around one clock rate than re-clocking isn't going to work. It's not like a RED sensor that was designed from scratch to be re-clocked.

squig
05-28-2009, 04:05 PM
I like this bit "Nikon is adding most of the same features soon in their cameras"

ok ok I'm outed I'm a closet nikon fanboy

If the 60D CMOS is better maybe it will be light on the jello

Pepster
05-28-2009, 04:24 PM
It's not always that simple. I'm not an engineer and I suspect no one around here is either. However, I know enough to know that if the sensor was designed from the ground up around one clock rate than re-clocking isn't going to work. It's not like a RED sensor that was designed from scratch to be re-clocked.
True, underclocking might not work, but then again, it might just work - surely it is worth a try for all those who live in 25fps land - will let them get their work on broadcast TV there.

I have mates who have been overclocking PCs for years, separately adjusting the clock speed of the CPU, IO bus, memory, graphics card, etc.

20% adjustment either way, and the PCs generally behave normally (simplified version...), but serious extra cooling is required at higher speeds. Some people have doubled the CPU clock by immersing it in lquid nitrogen... - but the CPU worked normally, just at double speed.

Slowing the camera down will not hurt it, and it will actually run cooler.

How this affects the CMOS sensor refresh, and thus the rolling shutter, is not clear - but it is worth a try.

Lee Wilson
05-28-2009, 04:39 PM
. . . surely it is worth a try for all those who live in 25fps land

Sounds great, I am in PAL land and would love 25p, how do I go about doing what you suggest ?

PappasArts
05-28-2009, 04:41 PM
It's not always that simple. I know enough to know that if the sensor was designed from the ground up around one clock rate than re-clocking isn't going to work. It's not like a RED sensor that was designed from scratch to be re-clocked.



How do you know that ? That's a confident statement. Inside info?

I'm more inclined to say it's possible no one knows truly what's going on in the cmos design and it's interaction with the digic chip set outside of canon or friends of Canon people..



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squig
05-28-2009, 04:56 PM
big rumor day http://nikonrumors.com/

Boz
05-28-2009, 05:35 PM
I hope they fix their skew problem.

caseyhayward
05-28-2009, 07:57 PM
big rumor day http://nikonrumors.com/

Seriously...is that all? Why is Nikon the one acting like they have a video division to protect while Panasonic and Canon release strong contenders?

ethan cooper
05-28-2009, 09:17 PM
Seriously...is that all? Why is Nikon the one acting like they have a video division to protect while Panasonic and Canon release strong contenders?

I don't get it either. I've been screaming as loud as I can on other message boards that Nikon is in perfect position to make a serious move in the DSLR video realm and they just keep not doing it. It baffles me.

Pepster
05-28-2009, 09:27 PM
Sounds great, I am in PAL land and would love 25p, how do I go about doing what you suggest ?

If I had a 5D2, I would locate the master clock crystal. Hang a CRO across it and work out the current running frequency - use the highest impedance probe you can so as not to load the crystal and this change the frequency slightly.

Get could get a new xtal cut - suck and see.

I havn't done this sort of thing for 15years (since CB radio days) but you can adjust the xtal f a few % with some capacitance loading across it.

But, personally, I would be looking at adding my own clock cct with a fixed f xtal on a small daughter board, with selectable clock division - eg 24, 25, 30 fps selectable. The cct is easy, making it small enough is hard ! It all depends on the currrent clock cct layout. eg, chaging the division with mostly Canon's cct may be possible (not likely).

The aim would be to get a stable 25fps working. The small % change to 24fps would then be easily achievable with a little extra capacitance loading - no further divisio changes would be needed.

I am almost tempted to buy a 5D2 just to prove it can be done (I might rent one...)

Digigenic
05-28-2009, 10:27 PM
Seriously...is that all? Why is Nikon the one acting like they have a video division to protect while Panasonic and Canon release strong contenders?
Nikon hasn't officially announced anything beyond the D90 and D5000 yet.
So, there's no need to get worked up over an unsubstantiated rumor regarding the successor to the D300, or any other camera for that matter.
Just be patient and we'll know soon what Nikon does.
For now, the 5DMk2 and GH1 are looking very good.

caseyhayward
05-29-2009, 05:03 AM
not getting worked up over here. Just thinking it makes sense that nikon might rush a crippled stop-gap cam to try to keep pace. I am well aware it is not a shipping camera but this has been a pretty good week for camera rumors coming true.

Lee Wilson
05-29-2009, 10:52 AM
If I had a 5D2, I would locate the master clock crystal. Hang a CRO across it and work out the current running frequency - use the highest impedance probe you can so as not to load the crystal and this change the frequency slightly.

Get could get a new xtal cut - suck and see.

. . .

But, personally, I would be looking at adding my own clock cct with a fixed f xtal on a small daughter board, with selectable clock division - eg 24, 25, 30 fps selectable. The cct is easy, making it small enough is hard ! It all depends on the currrent clock cct layout. eg, chaging the division with mostly Canon's cct may be possible (not likely).)

:huh: Oh! as easy as that is it !

In answer to your question: "I do not understand what is holding back all thoes who live in 25fps land" . . . the answer might be that the overwhelming majority of people don't understand any of the stuff you said !

:)

daveswan
05-29-2009, 11:04 AM
I do understand what Pepster is talking about, which is why I'm in no hurry to try it :Drogar-Dum(DBG):

shaocaholica
05-29-2009, 03:45 PM
The fact that they picked parts that were locked into 30hz and not even parts that could scale is just piss poor planning.

PappasArts
05-29-2009, 05:31 PM
The fact that they picked parts that were locked into 30hz and not even parts that could scale is just piss poor planning.

Amazing how unsubstantiated speculation, that has no factual merit to date, becomes fact. We don't know exactly what and how that CMOS intergeneration with the Digic chip set is working.

Posted this the other day:

24FPS is coming to the 5DMII, it's being beta tested at the moment. This has been in the air in LA film scene for a short while, however more confirms are coming in daily; not unlike the manual control chatter was two months ago, tell just recently. Then it happened.


DVXuser Timur Civan even has his own 1st hand account.

Conversation starts at thread #150 to be exact..

http://www.dvxuser.com/V6/showthread.php?t=172444&page=15



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.

shaocaholica
05-29-2009, 06:22 PM
Amazing how someone says an unsubstantiated statement that has no factual merit to date, and this becomes fact. We don't know exactly what and how that CMOS intergeneration with the Digic chip set is working
.

Wasn't the original rumor that the 24fps implementation was a hack? If its a hack then they obviously didn't plan to have it. If they planned to have it and didn't implement it on day 1 is pretty bad too.

However, if they do pull it off without any glaring artifacts then I applaud them. I'm sure they are also kicking themselves for not doing it from the start if the rumors are true.

PaulM
05-29-2009, 08:39 PM
I really hope they don't implement 24p by just slowing down master clock, unless it doesn't affect the CMOS read/reset speed. The CMOS readout is already a painfully slow 1/40s per 1080p frame. This has been established and corroborated by several users at cinema5d and dvinfo, Pango for one.

I'm trying to come up with an LCD shutter that will block light from the sensor for all but the period in which all pixels are simultaneously integrating. In 1080 30p mode, this period is just 1/120s per frame. The calculation is just (maximum exposure time per frame)-(read time per frame)=(maximum globally shuttered exposure). So with the same 1/40s read speed, 1080 24p could have a globally shuttered maximum exposure time of (1/24s)-(1/40s)=1/60s.

1/60 ain't too bad. If you shot 2.40:1 1920x800 24p, your read time per frame would be reduced to 1/54s. This would mean your maximum globally shuttered exposure time would be 1/43s. So Cinemascope 1920x800 24p with a 1/48 shutter would be totally doable. Even when factoring in the 1-3 milliseconds it takes to switch a high speed LCD shutter from an on to off state or vice versa.

Unless, in the process of implementing 24p, they slow down the CMOS read speed.