sigma MC-11 adapter fogs up with humidity?

[christoph]

We just had to stop a shooting because the image keept fogging up. Humidity is high here (80 - 90%)

My gear:

sony a6300, sigma MC-11 adapter, sigma art lens f2,8 14-24mm

I keep my gear in a dry cabinet when not used.

My guess is that the air inside the lens adapter fogs up when the camera heats up.

Any ideas how to deal with this best?

Thanks a lot for any advice

 

[Chrissie]

2 hours ago, christoph said:

My guess is that the air inside the lens adapter fogs up when the camera heats up.

This would be counter-intuitive. Fog builds up, when humid air cools below the dew point.

What makes you think it's the adapter that fogs up? Couldn't it be the lens?

[christoph]

hm, good point. the lenses are weathersealed so I assume no humid air gets inside the lens.

could it be that it's not fog but steam?

 

[Chrissie]

1 hour ago, christoph said:

could it be that it's not fog but steam?

There is technically no difference between "fog" and "steam". Both are just different names for "condensed water vapor". But this is not leading anywhere.

4 hours ago, christoph said:

I keep my gear in a dry cabinet when not used.

Assuming this cabinet is located inside your house, and that it's warmer inside your house than outside of it, the air inside your cabinet can hold more humidity in gaseous form (in absolute terms) than the cooler air outside.

Bringing this gear from the warmth inside your cabinet to the cooler outside eventually cools your gear off, so that the air trapped inside your gear reaches its dew point, et voilá!

Try keeping your gear in your car, parked outside of a garage, the night before you're going to use it outdoors, so it can accomodate to the conditions outdoors.

 

[christoph]

Dear Chrissi

Thank you very much for your reply, however my situation is a bit different from your assumption. Let me explain in more detail:

I live in a tropical climate, so most of the time the temperature inside my electric dry cabinet (around 28 Celsius) is below the outside temperature (30 Celsius and above). The dry cabinet dehumidifies to around 40%, outside it's 80 - 90%. When I take my gear out of the cabinet I wait at least 20 minutes before use to allow acclimatization.

The particular scenario yesterday was as follows: We were shooting in 120 fps for about 10 minutes without issues. See attached 3 stills from our video footage, pic1 beginning of a clip after shooting for 10 minutes, pic2 end of the same clip (blacks start to fade) and pic 3 still from a clip another 5 minutes later.

We stopped shooting at this point and I put all my gear into the dry cabinet again. Shooting in the afternoon the same day happened without issues.

I'd be very greatful for any further explanation of what could have been the reason for the foggy images and recommendation how to prevent this in the future.

 

P.S. I don't have a car ?

 

 

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[Chrissie]

Thanks "Newbie" (sorry for not knowing your name), for this clarification.

I'm afraid, in this case we'll have to dig a little deeper. I've annotated a diagram for this purpose. It's called a "Carrier diagram" or "Psychrometric chart".

For an explanation of scientific terms used, please refer to the respective article on wikipedia.

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Source/Author:  https://commons.wikimedia.org/wiki/File:PsychrometricChart.SeaLevel.SI.svg

This diagram tells you about various states of "moist air", containing more or less water in gaseous form.

• Along vertical lines the temperature remains constant.
• Horizontal lines are lines of constant water content, in grams of water per gram of dry air.
• The curved lines are lines of constant relative humidity.

I have marked the two states you mentioned:

• Blue star for your dry cabinet, at 28° and 40% relative humidity.
• Red star for outside condition of 30° and 90% relative humidity.

The large white area beyond the 100% relative humidity line (upper left) is where condensation occurs (the "foggy" area).
Note, that at the "blue star" state you are a very comfortable ~15° safety margin away from the condensation line, whereas at the "red star" state you are a mere 2° away from condensation conditions. Again, assuming, that the lens is mounted to the body at all times, within the dry cabinet and outside, you have a volume of air sealed inside your camera which contains ~10grams of water per kg of dry air. Since this volume is sealed, so is the absolute amount of water trapped inside. That's why you are moving along a horizontal line, when heating your gear or cooling it off. All you change this way is the relative humidity inside the sealed volume. You would have to cool this off by 15° or more, to have condensation occur inside your camera on any internal surfaces. Considering your operating conditions, there is no way how this could happen.

Also note, that your camera, after being taken out of the dry cabinet, is already 2° colder than outside conditions, which would completely eat up your safety margin from condensation start from the red star state. In that case, I would expect condensation to become visible on the outside of the front lens. Much like in winter, when people wearing glasses enter a heated room from the outside.

My recommendation is, to heat up your dry cabinet as close as possible to outside temperatures, to avoid this second type of condensation.

If that's not possible, then give your gear considerably more time than the stated 20 minutes, to accommodate to outside conditions, after taking it from the cabinet.

 

 

Edited October 10, 2018 by Chrissie

[sixzeiss]

You need to figure out where the fog/condensation is occurring. The sensor, the exposed side of the Rear element, the front element, or inside the lens.

There might be some benefit to storing the camera in your cabinet without a lens attached, so that humidity inside the body can be removed more effectively.