Thank you for your response Nancy.
Besides my background layer, I have one Adjustment layer open - Levels.
I create a duplicate background layer to preserve the original image, and do my Sharpening on the duplicate layer.
On top of the duplicate layer is my Levels layer, three layers in all.
I do not apply sharpening while on the topmost Levels layer, because from this layer the Preview screen does not show when I'm in the sharpening tool.
Instead of creating a duplicate Background layer I know that I can Convert to Smart Filter from the Filter menu to create a Smart object, but I instead use the duplicate layer - I don't know if this matters. I have tried both but the results don't seem to differ.
My blend modes are Normal and opacity at 100%.
My Smart Sharpen mode is at 100%, but it does not specify anything about opacity.
Your insights are appreciated.
For best results, you should perform all retouching & adjustments BEFORE you sharpen.
Then create a Stamp Visible layer on top with Ctrl + Alt + Shift + E (Win) or Cmd + Option + Shift + E (Mac).
This new topmost layer is the one you will duplicate and sharpen.
See this 11 min tutorial.
Are you viewing the image at 100%?
To evaluate sharpness and noise, you have to view the image at 100%, where one image pixel is represented by one screen pixel.Any other magnification will be inaccurate and misleading because the image has been scaled.
Thank you Per. This simple solution has helped. It would appear that when I sharpen an image which I am viewing at less than 100%, what I am adjusting is not translating across 100%. Makes sense!