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Sharpening

Three ways to produce sharp digiscoping shots

Sharpness is one of the biggest challenges facing those just starting digiscoping because image sharpness is not the same as the intensity of the subject, not to mention that the output medium is also a crucial factor. Digiscoping expert Dr. Jörg Kretzschmar describes how to achieve the sharpest photos through post-processing on the computer.

Autocontrast, well sharpened (Photoshop)

Dr. Jörg Kretzschmar is a biologist and came into contact with digiscoping through his work. He is regarded as one of the most high-profile digiscopers in the German-speaking world, whose photos constantly cause a stir. He uses an STX 25-60x85 spotting scope with a TLS APO adapter from SWAROVSKI OPTIK to shoot his photos.

Many digiscopers struggle with image sharpness at the start. In the majority of cases, you can achieve a sharp picture, but just not, unfortunately, at the place that is important for highlighting the subject. In this case, if you can dispense with your auto-focus and make adjustments manually, you are better off.

The human eye bases its impression of focus on differences in contrast. For instance, many images can appear sharper simply by adjusting the gradation curve across the whole image to form a slight S curve: the shadows become darker, the lights brighter. The result of this is a higher-contrast image that appears sharper. The methods used for sharpening in digiscoping are obviously different to those for adjusting the contrast.



Sharpening is only carried out on a computer

We have different options for sharpening images. As a general rule, you should only resharpen the image on your home computer and not via the camera itself while shooting pictures. If we resharpen the image at home, there are two important aspects to take into account.

Firstly, what can I use to achieve the best focus with my current subject?

Secondly, what is the purpose of sharpening it (Internet, projector presentation, output to film, or own print)?

The image should always be sharpened only at the end of processing because when contrast differences are amended, color changes can also occur, even affecting the thumbnails. If it is not clear what an image is going to be used for later on or how it will be presented, it should always only be slightly sharpened.

  • Original
  • Autocontrast (Photoshop)
  • Autocontrast, oversharpened (Photoshop)
  • Autocontrast, ok sharpened (Photoshop)

Three sharpening techniques for digiscopers

The best-known sharpening technique is definitely “unsharp masking.” This involves exaggerating the differences in sections of the subject like edges and structures, in a similar way to gradation, not across the whole picture, but only across sections of the picture.

The “unsharp masking” setting 30-45-0(-10) makes the image noticeably crystal clear. Apart from this main type of sharpening, there are a number of more complex filters derived from this, depending on the program.

If our subject doesn’t seem to have gained any benefit from these filters, sharpening in LAB mode is an alternative. This is done by converting the RGB image in Adobe Photoshop or a comparable program into LAB mode where only the luminance layer is processed using the known sharpness filter. But don’t forget to convert the image back to RGB mode; otherwise, you can expect to see a noticeable color shift when it is printed.

The third method for sharpening, which is also very suitable for birds’ plumage parts, is using the High Pass filter in Adobe Photoshop (available under the “Other” option). In this case, the light-dark contrasts are increased. In most cases, we only require a value between 2.5 and 3. You shouldn’t be shocked by the black and white transparency image. Since we’re processing a previously copied image layer with the High Pass filter, we can blend this filtered layer with our original image using “Hard light” mode. This method almost always enhances the image. If you find the effect too strong, you can reduce the transparency for the layer in Photoshop to 40 or 60%, thus adjusting the filter’s impact.



Errors to be avoided

Color errors, a seemingly overfocused image, and light-dark transitions that disappear and form bright fringes at the edges are just some of the things that shouldn’t happen when sharpening an image.