Common Digiscoping Photo Problems
Focus

Blurry, or out of focus photos are the most difficult aspect of digiscoping.

Photos are traditionally considered "in focus" if the eyes of the subject are sharp.

Due to the high magnification of the scope, the depth of field (how much distance in front and behind the subject is in focus) is very narrow. For close birds at a feeder, for instance, the head may be in focus and the tail out. A smaller aperture gives more depth of field, but also cuts the light down significantly. A smaller aperture may not matter, though, depending upon the exit pupil size of the scope's eyepiece compared to the aperture size of the camera. In other words, the scope eyepiece may be the limiting factor for depth of field, not the aperture setting of the camera. Experiment with different aperture settings and see if the brightness decreases; if so, then the aperture setting is making a difference on your setup. For most scope/camera combinations getting the camera lens as close to the scope's eyepiece as possible increases the effectiveness of the camera's aperture setting. (See Depth of Field by Digibird in the sidebar.)

Part of the subjective feel of focus is resolution--what is the smallest object that can be resolved to a single point? A smaller ISO gives better resolution. Pictures start to become grainy at ISO 200 and above. Use ISO 100 or 50, if possible.

If you look at your photos and the main subject is out of focus, answer these questions. Is anything in focus in front or behind your subject? Then you have bad focus. Is the area in which your subject sits in focus, but the subject itself is out of focus? Then your subject moved. If nothing is in focus, then you have camera movement, poor optics, or heat waves.

Causes/Solutions:

  • Bad automatic focus: Some cameras have known Automatic Focus shortfalls. Read the reviews. These cameras were not designed for focusing through a scope, so you can expect some challenges. The Automatic Focus on the camera is usually in discrete steps. The depth of field may be too narrow for Automatic Focus to choose the "perfect" focus. Most digital cameras focus on an area of strong contrast. That may not be the bird's eye--where you want to have the best focus. If there are branches in your shot, the camera will focus on those rather than your bird. Most cameras also indicate where they are focusing. If it is not on your bird, you won't have an in-focus shot. Digital cameras need ample light to focus properly. Smaller ISO numbers give sharper (less grainy) photos, but also require more light.
  • Bad manual focus: See the section on "Taking a photo" on the Techniques page and pay attention to the 2 focusing methods. It is very difficult to focus manually through the LCD. Unfortunately, with digiscoping, we don't have much choice. Shade the LCD viewfinder. Try the Infinite and Macro modes to see if one works best. Use a smaller aperture size and err on under-exposing. Err on focusing in front of the subject; two-thirds of the depth of field is behind the subject focal plane.
  • Camera/tripod movement: Wind may be a problem. Don't touch the setup when depressing the shutter button. How? Use a remote shutter release or use the camera's self-timer delay. If depressing the shutter manually step down half way to focus and set exposure, then smoothly depress the shutter fully.
  • Subject movement: You'll see a lot more digiscoped photos of big birds that stay still (herons, hawks, and ducks) than smaller, active birds.
  • Poor scope optics: If you are using a cheap or dirty or fogged scope you won't get the best results.
  • Heat waves: A sunny winter day came up last month so I finally got out to take some pictures. I couldn't focus my scope on the sparrows down the path from me just a short distance. Heat waves were the problem. This will happen any time there is a difference in temperatures of the air through which you are focusing. It is usually worse close to the sun-heated ground.

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Focusing links...

Focus by Digibird

Depth of field by Digibird

Optics math by Digibird

Excel spreadsheet for computing optics math by Digibird

Fine Tuning sharpness by Short Courses

Digiscoping 101 with Don

Purple fringe: chromatic aberrations

Chromatic aberration is the inability of a lens to focus all colors to the same point. Problem is found in the camera lens, the scope lens, or both.

Purple fringe occurs where bright images are adjacent to dark regions. The bright areas bleed over into the dark area with an annoying purple color.

In advanced photo editing software you may reduce the intensity of magenta and turn it gray. However the clone tool seems to work best in some situations to grab the color of the background nearby and paint it over the purple fringe. Here is an example of a blown up portion of a photo. The egret photo had a purple fringe all down the neck and across the back on the sunny side of the bird.
purple fringe

The clone tool takes care of the problem.
Great Egret


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Chromatic aberrations...

Chromatic aberrations by Botzilla.com

Chromatic aberrations by Digital Camera Experiments

Fixing chromatic aberrations by Digital Photography Review

Blown highlights: over-exposure

Once the white is saturated, there's not much you can do. Expose for the highlights, you can always lighten later with the photo editing software. It is better to under-expose than over-expose.

The highlights are blown-out (over-exposed) on this shoveler. Even darkening the photo would have no effect--you could darken until everything else was black, but those white areas would still be there. I reduced the photo to a small size which had the additional benefit of hiding the purple fringe on the breast and making up for the fuzzy focus.
Northern Shoveler


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exposure links...

Vignetting

Vignette ("vin-YET") is the word for the dark circle around your view through a scope or binoculars. In digiscoping, this vignetting is eliminated by increasing the magnification on the camera until the camera can no longer see the edges of the dark field. Vignetting disappears on most digital cameras at about 3x. The photo below is 1x on the camera and 20x on the scope.
Vignetting


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Vignetting links...



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