long exposure problems

[geoff tompkinson]

When doing exposures approaching 1sec in length one starts to see a starfield of fixed position coloured pixels mainly red and blue.

These are visible both on the lcd and in the final file.

They can be masked to some degree by dropping the ISO rating to 100. and further improved by doing a black calibration at these settings.

If the ISO rating is increased the pixels become more and more defined until at very high ISO settings the starfield becomes a galaxy.

It seems that these pixels are there all the time but are normally masked when the light level hitting the sensor is above a certain threshold.

My question is can someone explain why these pixels are visible at these settings when with the Canon dslr's - also cmos based - this does not happen.

You may wonder why any of this would be of concern. Well I produce a lot of time lapse clips using settings like this to achieve a fluid ghost like movement. With a dslr I have no problem. With the Red the shot is not suffering from noise in the sense of heavy moving grain but is ruined by random fixed position coloured spots.

 

[Vigen Vartanov]

Same Problem

Same Problem

We have 100 % same problem . We shoot TL with 1/2 shutter .
As i read on reduser you need to make BSH every time you go to 1/2 shutter and back. But it is not help .

 

[Lewis-M Soucy]

When changing exposure time, every time you change it, you MUST perform a black calibration. Same when you set it back. I've read a lot about this on the forum... Hope this helps...

 

[T. Glen Phelps]

I have the same problem.

 

[Vigen Vartanov]

Black calibration can not help me . I also read about it , but still no result.

 

[T. Glen Phelps]

Black Shading does not help.

 

[Vigen Vartanov]

We lose some dark footage because of this problem .
Can some body from RED answer as

 

[David Wilson]

I have the same problem and black shading sadly does not seem to help.

 

[LEON]

The only correct setting I found in time lapse or frame by frame:
exposure should NOT last longer than 1/16 of a second or then you discover the limits of the sensor and they are visible, black shading does nothing to this.
Very infortunate.

 

[geoff tompkinson]

The only correct setting I found in time lapse or frame by frame:
exposure should NOT last longer than 1/16 of a second or then you discover the limits of the sensor and they are visible, black shading does nothing to this.
Very infortunate.

If you do a black shading first then shoot at 100asa you can get perfect results with a 1/4sec and pretty near perfect at 1/2sec.

But what I would like someone with some technical savvy to explain is why these colored pixels rear up at these settings with the Red when I've never seen them in any other digital camera.

 

[LEON]

If you do a black shading first then shoot at 100asa you can get perfect results with a 1/4sec and pretty near perfect at 1/2sec.

But what I would like someone with some technical savvy to explain is why these colored pixels rear up at these settings with the Red when I've never seen them in any other digital camera.

Well, you are lucky !
I hope you will agree than the recorded RAW is just the same whether you set 100 or 1000 ASA ?
Setting 100 ASA instead of regular 320 just hides the issue in the LCD or EVF but not on the recorded file, do we still agree ?
So you could just expose at regular 320 and hide in post with adequate toe in Redcine or Redalert or whatever software.
The issue remains, (blue and red tiny spots extremely visible in shadows, visible in middle lights and of course hidden in highlights) and, here, Blackshading DOES NOT do a thing, unfortunately !
And where I agree with you, the Canon20D or 40D does not do that,
so who could explain us what is going on ?
DEANAN, STUART, GRAEME? help !

 

[geoff tompkinson]

Well, you are lucky !
I hope you will agree than the recorded RAW is just the same whether you set 100 or 1000 ASA ?
Setting 100 ASA instead of regular 320 just hides the issue in the LCD or EVF but not on the recorded file, do we still agree ?
So you could just expose at regular 320 and hide in post with adequate toe in Redcine or Redalert or whatever software.
The issue remains, (blue and red tiny spots extremely visible in shadows, visible in middle lights and of course hidden in highlights) and, here, Blackshading DOES NOT do a thing, unfortunately !
And where I agree with you, the Canon20D or 40D does not do that,
so who could explain us what is going on ?
DEANAN, STUART, GRAEME? help !

No we do not agree exactly.

If you shoot a 1 sec exposure and rate the camera at 320 you will naturally close down (in comparison to rating at 100) to get the exposure looking correct. If you do a 1 sec exposure at 100 asa you will open up (in comparison to rating at 320) in order to get the exposure correct. It is the act of opening up as a consequence of rating the sensor at 100 asa that lets more light to the sensor and improves the result.

Clearly if you shoot 1 sec with the same aperture then changing the iso makes no difference at all because the sensor has received the same amount of light.

Arguing the obvious does nothing to help answer the question and at least you agree with that.

So perhaps we will hear something from the guys in the know on this.

 

[LEON]

No we do not agree exactly.

Arguing the obvious does nothing to help answer the question and at least you agree with that.

So perhaps we will hear something from the guys in the know on this.

Sorry, sorry, for arguing the obvious, will try not do to again, please forgive froggie mistakes ! SMILE

 

[JohnF]

Anyone fancy posting some stills of these artefacts?

JohnF

 

[David Nardini]

With all the good stuff posted at : http://www.reduser.net/forum/showthread.php?t=20347

Can anybody from Red chime in on this thread ???

Cheers ...