A big problem for amateur photographers is to increase the quality of their equipment without having a good economic income given by photography. At the beginning it is easier for the most to choose low level cheap lenses which lack in quality, especially in sharpness.
This photo has been taken with a Sigma 70-300 Apo Macro Super at 300mm:
This is a crop of the same picture without any resize, it is possible to notice a huge lack in sharpness
This effect can be caused by many factors like exposure time, f-number, lens quality. Adobe Photoshop CS and furthers contain a nice tool to correct this defect at least partially. You can open it with Filter > Sharpen > Unsharp Mask.
It works very easily: the algoritm scans the pixels of the image and estimates the contrast between closed pixels or closed areas. If this contrast is higher than a manually choosen threshold it is interpretated as information of a detail and the algoritm amplifies it. In other words the USM filter can render the edges of the objects in the picture more clear, but it is important to keep in mind that this algoritm does not recognise the edges, but only the differences in contrast.
The palette of the unsharp mask filter has three parameters that has to be properly setted up:
Normally, I act in this way:
1. Start with a high amount value to better notice the differences.
2. Gradually increase the radius until you see a nice result. Don't worry if the edges are too black and strong, we are going to correct them.
3. Reduce the amount value and increase the threshold in order to equilibrate the image and correct the edges. The rest of the image is sharper.
That's it! Before and after:
You can always contact me if something is not clear!
