Is this heat distortion?

[l9magen]

I was going through some old pictures that I had not looked at since uploading to LR a few years ago. I was using a Canon 5Dii with a C/Y Zeiss Vario-Sonnar 100-300mm. I have lost the notes I'd take when using a lens where the EXIF won't be correct, so I have no certainty as to the aperture or the focal length, but would guess it's f11 somewhere close to 180-200mm.

Other shots taken that day are tack sharp, no distortion at all, regardless of the distances involved. Later shots (later in the year) are also tack sharp, even when shooting detail on mountain tops at sunset at 300mm. So I don't think it's the lens.
Here's the issue, from a 100% crop in th centre of the shot.....that telephone should be straight, as should the fence posts.
I'd be happy to hear any ideas on what is going on, and what I might do to counteract it in future.
Lochlann

[cooltouch]

Most likely. Was it a warm to hot day? If you took more than one photo, was there any difference between the two? If yes, definitely atmospheric convection currents are messing with your shot.

[l9magen]

Yes Michael, it was a warm prairie day, and from a separate shot I guess there was very little wind too.
So would the advice be to perhaps leave telephoto lenses at home on hot, still days?

[cooltouch]

Well, the convection currents can definitely spoil a shot, especially when a telephoto is used. Then again, they can make interesting effects in extreme cases:



Taken with a 300mm lens. The above aircraft is an AV-8b Harrier, used by the US Marine Corps. It is a vertical takeoff and landing (VTOL) plane. It has ducted exhausts, which are directed downward when the pilot wants to take off vertically. Such was the case above, and the convection currents caused by the intense heat of the exhausts gave an interesting effect, I thought.