Object distance (1 Viewer)

How can I calculate the distance to an object if I digiscope it? I imagine that knowing the aproximate size of the object would help. I want to compare different eyepieces and this information may be useful. I use a pentax PF80A and a CP4500. Thanks, Jose.

Jose,
You could try this:- Take a six inch ruler and put it at a measured distance, say 40 yards. Look through the scope and see how much of the field of view it fills. Make a note of this. Repeat with other distances. Say the ruler spans half the field of view at 40 yards. You then know that an object which is roughly six inches long and spans half the field of view is 40 yards away. As you say, this method does depend on knowing the rough size of the object you are looking at - not too difficult with birds. However, it could get difficult when you are using the zoom on the camera and the zoom on the scope, so you may need to make up a table of results covering each possible combination. Hope that helps!
Cheers, Pete.

mmdnje said:

How can I calculate the distance to an object if I digiscope it? I imagine that knowing the aproximate size of the object would help. I want to compare different eyepieces and this information may be useful. I use a pentax PF80A and a CP4500. Thanks, Jose.

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Jay Turberville has made this very easy for you. Just enter your scope power, camera, zoom, resolution etc. in this "Digiscoping calculator" http://www.jayandwanda.com/digiscope/digiscope_calc.html and press the buttons. Say, a 30cm bird photographed at 20x (+ camera zoom at 18 mm) spans over 100 pixels in the picture => the distance to the bird was about 343.76 meters.

Ilkka