Hi Glenn
Thanks for your comments. With regards to the lens, it is a top quality lens with at high rating from independent sources and i can only assume that it's not the lens as all my other photos taken the same day were OK (see the 'White-browed Scrubwren' photo I submitted earlier). The testing of the lens was rather detailed, which I will explain to you via e-mail, but I used the AF Fine Tune function on my D500 and as a side note I took 500+ photos at Gluepot over the last few days with a higher "in-focus" success rate than before, so I believe the testing has improved the focus. In addition I will start using a higher aperture to increase the depth of field as suggested when light permits.

With regards to post process sharpening, I did no additional sharpening to this photo other than Lightroom sharpening and 'Smart Sharpen' in Photoshop after reducing the photo size to meet the requirements by BLP. This sharpening is in line with your recommendations to me when I first started with BLP and it is the method I now use with all my photos.

Regards
Gunther

Thanks for the offer Les. I live in Gawler approximately 60 K's from Thompson's Beach and would be glad to catch up with you to look at this "Lensalign" device. I have nothing planned for the next two weeks and if its easier for you to meet closer than Thompson's beach let me know. I will message you from one of your photos which will provide you my e-mail address.

Thanks again.
Regards
Gunther

Hello Gunther,

Les has diagnosed your problem correctly; your image quality was degraded by refraction in the air due to heat. This is a common problem encountered when shooting over warm ground and can restrict photography to the early part of the morning.

In your image there are some out of focus highlight spots in the background. In the ideal situation these will appear as a circular patch of light with concentric dark rings. Technically speaking, these rings are due to the diffraction of an incoming spherical wavefront from the edge of the lens aperture stop. When the light path from the highlight twinkle is disturbed by heat haze, the wavefront propagating through the air from the twinkle is no longer spherical but a much more complicated surface. When this complex wavefront is diffracted by the lens aperture the out of focus highlight is no longer a set of concentric rings but something more like spaghetti. When you see out of focus highlights scrambled in this way you immediately know that heat refraction is degrading the image quality. Unfortunately, there is little one can do when this situation arises. It varies rapidly with time so by taking many frames one can get a lucky break and it varies quite a bit from place to place so frames captured tens of metres away may be OK. When I encounter this problem, I usually stop shooting and use the time for some other activity.

Hope this helps,
Ian

Thanks Ian, your comment was helpful. Clearly when I next go out to photograph shore birds, I need to get out early and if the temperature warms up, do something else. I will experiment more with shutter speeds and aperture as suggest by both Les and Glenn. I am learning more as i go along and hopefully will soon score some good shore bird photos.
Cheers
Gunther