Hi Simon,

Thanks for the list of items to consider.

Car engine was not running and the image not captured through glass. Other occupants were also motionless. No filter and shutter speed would have been in the order of 1/800 @ 600mm as I recall.

It was quite a cool day and I do recall wafts of heat hitting me, that I can't think would be coming from anywhere else other than radiating from the bonnet.

Best regards,
Craig

Hi Craig

I am struggling a bit to picture your situation;  for example you are in the driver or front passenger seat, looking out the window, how are you shooting across the bonnet (unless you are hanging half out the window which would make it almost impossible to hold the camera steady).  However, that doesn't ultimately matter.  It is certainly true that air movements due to heat can cause distortion and affect sharpness, so this is one possible cause, although it is to some extent distance dependent.  It may be unnoticeable if the subject is near, but will certainly get worse with more air between you and subject.  As I said, there would be several other possible causes and all you can do is try and eliminate those as a possibility.

My list of things to check for sharpness generally includes:  subject motion (not likely to be a cause with this shot); camera motion (IS on or off? is IS in the right setting? fast enough shutter speed for focal length?  steady platform?); lens and camera (high megapixel cameras are very finicky/demanding and amplify sharpness problems due to small pixel size;  poor quality filters; lens sharpness generally at focal length used);  air effects (heat particularly over distance); shutter shock (using mechanical shutter?);  post-processing issues such as noise reduction and cropping.

It is probably easy to test the bonnet heat theory by shooting some test shots in your own drive over a hot engine, in a controlled way (eg camera on a tripod to eliminate other sources of blurring, static subject, still day) and compare directly with the same subject shot away from the bonnet at the same distance.

Simon

A timely video from Steve Perry on this topic.