Effect of heat & humidity on IQ?

[lowep]

Hi, I am looking through my images after an outing with a Sony A7II and 35mm Zeiss lens in quite a hot and humid environment and notice that in some images the complexions of the subjects are smeared like melted chocolate, though details such as the same subject´s eyes, jewellery, patterns on clothing etc are quite sharp, somewhat as if the images were exposed at very high iso though they were not. I noticed at the time the camera was quite warm though seemed to perform as it should with no problems. So am wondering if overheating or condensation on the lens or sensor that I did not notice could have caused the effect I mention? Maybe there could be some other cause... me for example... that I have not thought about?

[Rob C]

I notice that my IQ has gone down a little bit after living so long in all this heat and humidity.

Perhaps that explains Key West.

Rob C

[lowep]

I notice that my IQ has gone down a little bit after living so long in all this heat and humidity.

Perhaps that explains Key West.

Rob C

according to wallace stevens the effect should be the opposite: "in ghostlier demarcations, keener sounds." - but he was a poet not a a photographer so his point may not be relevant to the subject of this thread :-)

[shadowblade]

1. Heat has an effect on noise levels in long exposures - a higher ambient temperature means more long-exposure noise. Not because the atmosphere heats up the sensor, but because the rate at which the sensor can cool depends on the difference between atmospheric and camera temperature. Less difference = smaller temperature gradient = less cooling = less noise.

2. Heat - or, more specifically, localised difference in air temperature - also has an effect on atmospheric refraction. This is more pronounced when shooting with long lenses, since there is more atmosphere between the sensor and the subject, and greater magnification (there may be kilometres of atmosphere between the sensor and subject in a wide-angle landscape shot, but the effect isn't magnified as much as when shooting at 800mm). When shooting inside or over a volcanic crater, this effect is so pronounced it's near-impossible to get a pixel-sharp shot of magma or lava, even at 200mm.

3. Humidity should have no effect - provided the temperature of the sensor is similar or higher than the atmosphere, there should be no condensation on the sensor.

[Paul2660]

Doesn't relative humidity and thus the heat index play into this also? 

I know that Phase One is very clear out the ambient temp and humidity for using both their CCD backs with long exposure capabilities (P45+ IQ260 etc) and the new CMOS backs,

For 30 minutes to 1 hour outdoor temp of 69 degrees F or lower and humidity in the 85% or less range.

Just curious.   The Sony A7rII has a heat issue with long exposures and use with with video especially 4K.  Sony's answer was to always us the Long exposure noise reduction which works fine on simple astro work, or daylight long exposure, but really can't use it with stacking.   Fuji X-Pro2 shares the same issues, heat build up around the grip, and excessive noise.  New batteries from Fuji may help on this soon.   

Paul C

[lowep]

1. Heat has an effect

Thanks Shadowblade for your very precise reply that seems to indicate I can most likely rule out heat and humidity as the cause of the effect I am seeing as the exposures were not long, the subjects were not far away and there was no volcano. What you say about heat also explains why my camera body got warm that it has never done before and has not done again since.