Puzzeling noise in dark area of 5D photo

[martin nillesen]

Hi,

I am confronted with a puzzeling noise in all shots taken in the same portraitsession. The session took place at the studio of a collegue. As you can see in the pic the noise is most visble in the dark areas about half the frame ( in protrait-mode left, in landscape mode from the top down.) I can't figure out whether this noise is due to:

A underexposure. Although this shot is underexposed a half stop, it doesn't explain the partail noise.

B Wrong speedsetting (AV mode 1/125th at f14, strobespeed 1/60th brand elinchrom RXseries, In the menu (C.fn 03) of my 5D flashsync speed in AV mode on camera set to 1/200th fixed) According to these settings shots should come out fine. To me it looks like a wrong sync setting but I can't put my finger on the source of the noise. When I deliberately set my camera to a speed of 1/200 and f14 in Manual the image is half darkened, but no noise! The flashsync should work up to a speed of 1/200th.

C Defective CF-card. When discovered the problem I reformatted the card, took some shots with my own strobe (elinchrom Dlite400) and no noise showed up, but again 1/200th was partly darkened.

Is the anyone who can shed some light (!) on this problem?

See the ^#$#%!! PIC HERE!

Martin Nillesen.

[ChrisPerry]

In the studio you should be shooting in manual mode - 1/125 for the shutter and whatever aperture you want/is correct. Not aperture mode.

As to the 'noise'...looks like electrical interferance to me as opposed to ISO noise or some such issue.

perhaps someone else here has seen something similar and might shed some light on this.

[Martin_Doudoroff]

Looks like an electronics problem to me. You need to test the hell out of the camera and see if you can establish consistent reproduceability.

[AndrewCassino]

In particular, this looks like radio frequency interference. Were you using radio triggers? Perhaps there is some timing overlap that allows the 1/125th shutter speed to "capture" some of the interference, but the 1/200 shutter speed excludes it.

By the way, there is one particular location here in Seattle where I always get a (somewhat) similar interference pattern with my 5D, but only with one particular lens attached. All I can assume is there is some concentration of radio signals at that location that the camera is susceptible to. It is the only place where I get the interference!

[Ross Becker]

Hi Martin
As a retired electrical engineer, I too think that this is interference from the high frequency power oscillator in the flash getting into the 5D.
The interference may be getting there in one or more ways:
1 Through the sync cord if you're using one,
2 Through the radio sync if you're using that,
3 Directly by RF radiation from the flash

1 Can you borrow a different flash - see if the interference changes/disappears
2 Set up the flash much further away from the camera and see if the interference reduces. Try & double the camera/flash distance as a trial.
3 Can you get a ferrite core and put several turns of the sync cord through it,- as many computer & camera cables now have. This should stop the interference travelling down the cord.
4 Wrap aluminium foil around the camera as a RF shield & check the result

All the best at fixing the dilemma.

[martin nillesen]

Originally Posted by ChrisPerry

In the studio you should be shooting in manual mode - 1/125 for the shutter and whatever aperture you want/is correct. Not aperture mode.

As to the 'noise'...looks like electrical interferance to me as opposed to ISO noise or some such issue.

perhaps someone else here has seen something similar and might shed some light on this.

Thanks Guys,

The incident occurred when I was shooting at the studio of a collegue. I indeed shot with a radio sync, but also a lot of onther collegues were standing around me and we either shooting with their own flash on the camera, which was very annoying, because the studioset was set to slave and reacted on the flashes going off constanty, or one of the Elinchrom strobes wasn't working allright (RF disturbance?).

I extensively tested my own two Elinchrom D-lite4's with my own Radio Sync and everything was fine. So I guess the problem isn't resident in my studio.

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