Question about heat distortion

[SCoombs]

As part of my testing of the 180-600 as I've been discussing in other threads I've been going to a local pond here and there. Each time I've gone I've encountered heat distortion that behaves differently than I expect.

First, note that in each case it's been in the 30s or low 40s F, mid afternoon, and with maybe intermittent sun but generally cloudy.

Now I've gone there in the summer and am used to getting midday distortion over the water on many days. On those days the only great shots I tend to get are birds walking around on the ground.

I've also gone in the autumn without any distinct pattern I can recall.

These past two times though with the weather I've described I've experienced AWFUL distortion over the ground and much better results over the water! In the summer the distortion makes photos look rather soft, but this is just making almost every shot over land look like the focus ring was rotated a bunch after focus was acquired. It is distortion, though. Meanwhile, over the water things look either like the normal distortion I see in the summer OR pretty clear.

I even noticed that if I focus on a subject over land and watch the out of focus area on the viewfinder I can see the air shimmering like what they do to introduce a dream sequence in a television show, or as though there are many currents of air I can see moving across the frame.

Any insight here as to why I'm seeing such bad distortion over the LAND while the water, where I'd usually expect distortion, is so much more clear?

 

[DRwyoming]

Any insight here as to why I'm seeing such bad distortion over the LAND while the water, where I'd usually expect distortion, is so much more clear?

A lot of what we think of as Heat Distortion is turbulence in the air. The turbulence is created by different temperatures and typically rising warm air. It can happen on quite cold days if there's local heating like shooting across asphalt on a sub zero day where just the sun warming the asphalt can create rising warm air and turbulence even though the actual temperature is very cold.

From what you describe I'd guess that the land is fairly warm relative to the sun and the water you're shooting across isn't quite as warm relative to the air so it creates less thermal rising and less turbulence.

 

[DsD]

Probably due to the land being warmer than the water and radiating the head back up; The water is still absorbing.

 

[NorthernFocus]

Thermal distortion is caused by differential temperature between the camera and target. Typically the problem occurs when the surface temperature is higher than air temperature. As the air near the surface warms it rises and that's what causes the distortion. So regardless of whether the surface is ground or water if it is warmer than air temperature it will cause thermal currents and therefore distortion. When the air is warmer than the surface it's typically not an issue. So in warm weather we don't typically see distortion shooting over water due to it being cooler than the air. In winter that is often reversed with the water being warmer than the air.

 

[Ralph]

As part of my testing of the 180-600 as I've been discussing in other threads I've been going to a local pond here and there. Each time I've gone I've encountered heat distortion that behaves differently than I expect.

First, note that in each case it's been in the 30s or low 40s F, mid afternoon, and with maybe intermittent sun but generally cloudy.

Now I've gone there in the summer and am used to getting midday distortion over the water on many days. On those days the only great shots I tend to get are birds walking around on the ground.

I've also gone in the autumn without any distinct pattern I can recall.

These past two times though with the weather I've described I've experienced AWFUL distortion over the ground and much better results over the water! In the summer the distortion makes photos look rather soft, but this is just making almost every shot over land look like the focus ring was rotated a bunch after focus was acquired. It is distortion, though. Meanwhile, over the water things look either like the normal distortion I see in the summer OR pretty clear.

I even noticed that if I focus on a subject over land and watch the out of focus area on the viewfinder I can see the air shimmering like what they do to introduce a dream sequence in a television show, or as though there are many currents of air I can see moving across the frame.

Any insight here as to why I'm seeing such bad distortion over the LAND while the water, where I'd usually expect distortion, is so much more clear?

It is quite normal, especially at that time of day. I’ve been experiencing it a lot, especially after 10am. Usually the camera has a tough time getting a focus lock.

 

[SCoombs]

Thermal distortion is caused by differential temperature between the camera and target. Typically the problem occurs when the surface temperature is higher than air temperature. As the air near the surface warms it rises and that's what causes the distortion. So regardless of whether the surface is ground or water if it is warmer than air temperature it will cause thermal currents and therefore distortion. When the air is warmer than the surface it's typically not an issue. So in warm weather we don't typically see distortion shooting over water due to it being cooler than the air. In winter that is often reversed with the water being warmer than the air.

To be clear, what's got me confused is precisely that it was over the land rather than the water, where I'd have expected it. I usually see it over water in the warmer weather.

 

[Ralph]

To be clear, what's got me confused is precisely that it was over the land rather than the water, where I'd have expected it. I usually see it over water in the warmer weather.

I experience it over land all the time. It’s can be very frustrating. Like I mentioned above, it’s very normal after 10 am in the northeast. I thought there was an issue with my lens when I first experienced it. When I got home, everything was working normally in my back yard. I went to the refuge the next day and in exactly the same area at the same time of day it happened again. Last Thursday I went out shooting but arrived late morning. I should have stayed home. When I went on Monday, I arrived at sunrise and had no issues until around 10 am.

 

[Warren D]

Land tends to absorb heat more efficiently than water and thus radiates that absorbed heat more. As said several times already, it's from heat differential, usually where the air is cooler than the land or water although I've seen it when the air is warmer, a thin layer forms right at the surface. Wind enters in as well, in short it seems there are multiple factors involved some of which seem counter-intuitive. Clouds still allow lots of UV rays thru which heat surfaces. Some of my worst sunburns have been on cloudy days.

 

[SCoombs]

Land tends to absorb heat more efficiently than water and thus radiates that absorbed heat more. As said several times already, it's from heat differential, usually where the air is cooler than the land or water although I've seen it when the air is warmer, a thin layer forms right at the surface. Wind enters in as well, in short it seems there are multiple factors involved some of which seem counter-intuitive. Clouds still allow lots of UV rays thru which heat surfaces. Some of my worst sunburns have been on cloudy days.

I understand how it works, I've just never in the years I've been doing this encountered it other than over water. In fact the way it's always been is that when I do experience it, always over water, switching to the land has eliminated the problem.

 

[SCoombs]

Here is a video I took of this yesterday, best visible full screen at the 4k resolution setting and very hard to see at standard definition resolution.. One thing that I don't fully understand is that the duck looks alright in this video but any attempt at a still photo looked essentially like the out of focus seagulls do in this video.

 

[cchuck]

The problem is exacerbated by super telephoto lenses that lure us into shooting subjects from greater distances -- through more refractive soup. Also, shooting subjects at ground level involves rising heat nearest its source (soil, water, grass, pavement, etc.) Later in the day is a good time to shoot birds in flight, ie. soaring raptors.

 

[Ken Miracle]

I understand how it works, I've just never in the years I've been doing this encountered it other than over water. In fact the way it's always been is that when I do experience it, always over water, switching to the land has eliminated the problem.

Atmospheric distortion can come over any surface it is the temperature differential between the surface shooting over and the air column being shot through.

As @Steve has demonstrated and discussed in many videos and I have demonstrated to a lot of people it can also be cause by shooting out of a heated or cooled vehicle with the air from inside the vehicle coming out the open window and causing the temp differential and distortion in front of the lens. It can also come from warm air trapped in the lens hood on a cold day when you take the lens from a warm vehicle or building outside and start shooting immediately. Solution take the hood off for a bit until it and the lens cool down or let the camera ride in the cold vehicle to get to the about the same temp as the air your going to shoot in before you start shooting, if you may be shooting from the vehicle the heat needs to be off anyway

 

[SCoombs]

I went out again today. Anyone ever get this for birds in the air? I'm not talking about at water level, but literally up 20 or 30 feet in the air, though above water.

 

[Woodyg3]

I went out again today. Anyone ever get this for birds in the air? I'm not talking about at water level, but literally up 20 or 30 feet in the air, though above water.

I've gotten plenty of heat distortion on airplanes that high over a hot runway, but not birds over natural surfaces as far as I remember.

 

[SCoombs]

I've gotten plenty of heat distortion on airplanes that high over a hot runway, but not birds over natural surfaces as far as I remember.

Well, see my latest comment in the "Nikon Z 180-600 Test shots" thread as I now am not sure whether what I am seeing even is thermal distortion, though I think it's been a factor.

 

[nautiboy]

I went out again today. Anyone ever get this for birds in the air? I'm not talking about at water level, but literally up 20 or 30 feet in the air, though above water.

Oh absolutely. I've gotten heat distortion on birds even higher than that. Any time there is a mix of warm/cold air *anywhere* in the air column between you and the subject you can get it. A raptor riding a rising warm air current, with cool sea winds blowing in .... warm air blowing in from inland and greeting cooler air from the coast .... I've run into that more times than I can count. But I live on the coast side of a large hill. It is not unusual for the temperature to be more than 30F difference in less than a mile, if you go from one side of the hill to the other. Riding my motorcycle home from work, on those days where it's 90+F inland and I'm coming home in my heavy leathers, I live for that moment when I crest the hill and it goes from 90F to 60F in an instant.