Oil film reappearing on sensor

[Xiaosu]

Hello,

we have a problem with one of our Alexa 35s on a shoot in Thailand,

we have found a kind of oil/smudge film on the sensor/OLPF

cleaned it properly -

but after a week and a half if reappears

anyone had something like that before??

thanks and all the best

[Andreas Berkl]

Dear Xiaosu,

what you describe could be condensation of water on the cover glass of the sensor. If the ambient temperature is high (around or above 40 degrees centigrade) and the air is very humid (aka tropical climate ...) this can happen. So Thailand may be a candidate for this.

Is the effect visible in the image? If so, please email a frame grab to digitalworkflow at arri.de.

Condensation may easily happen before the sensor has reached its target temperature of 40 degrees centigrade. Also storing the camera i.e. in an air-conditioned hotel room and then bringing it out into a hot and moist environment is not a good idea.

Typically condensation visible in the camera's image will form up from the top of the image. That's because the image top is the sensor bottom - which is a bit colder than the top and may attract water (damp) earlier.

Try to check the cover glass visually, maybe with a magnify glass. Cleaning should help, but as you mention, condensation may re-appear as soon as the environment gets critical.

Hope this helps!

Best regards.

[Xiaosu]

thanks so much for the fast reply

what I havent mentioned is that we have two other 35s

that don’t exhibit that problem at all and are used in the exact same conditions

what else could be the culprit??

thanks

[Xiaosu]

thanks so much for the fast reply

what I havent mentioned is that we have two other 35s

that don’t exhibit that problem at all and are used in the exact same conditions

what else could be the culprit??

thanks

could a different fan setting create a different “enviroment” around each camera?

[Andreas Berkl]

Dear Xiaosu,

okay, having another camera not showing the issue indeed makes it unlikely. However I would not totally exclude the possibility, that the "macro climate" slightly differs between the two cameras.

It could also be that the affected camera has some moisture in the room in front of the cover glass and the other not.

What you could try is to power the affected (or both) camera(s) in a warm BUT DRY environment with no lens/lens cap. This should vaporize the moisture pretty fast and get it out of the sensor's cave..

If you are shooting in a warm & humid environment, also make sure to change lenses as fast as possible to avoid moist air to settle inside the camera.

[Andreas Berkl]

> could a different fan setting create a different “enviroment” around each camera?

Yes, indeed. If set to REC LOW, the camera gets pre-cooled and thus have a higher probability to show condensation.

[Xiaosu]

we managed to snap a picture… this is after a few hours of shooting, after having been cleaned in the morning - the other two cams are fine

all cameras are on rec low -

we might have it cleaned again professionally at a facility next..

and try the hot room too - could it be that the camera has been used in a very very humid enviroment before and that some residue water is trapped somewhere??

thanks!!

[Andreas Berkl]

Hm, the image is pretty fuzzy. Hard to tell anything from it ...

Can you please post a JPEG grab (with lens of course and properly exposed) here - or send it to digitalworkflow at arri.de? This would make it much easier to get to the bottom of the issue.

> all cameras are on rec low

If possible, please try LOW NOISE.

> could it be that the camera has been used in a very very humid enviroment before and that some residue water is trapped somewhere??

That's indeed a possibility.