jschock said:
Can someone tell me how to calculate the correct distance required to fill the frame. example:
a 5" tall bird. What distance would I have to be using an equivalent 800MM (500MM +1.6X crop factor) slr lens to have the frame filled on My Canon D60.
Jeff
Jeff -
This is just a repeat of my post at Digiscoping-birds. I didn't bother to recalculate for a 5" versus 4" bird though. Posted here for others who don't visit there.
You could use my Discoping Calculator for this.
http://www.jayandwanda.com/digiscope/digiscope_calc.html
1) Choose the Canon 10D on the pulldown. I'm pretty sure it has the
same sensor size as the D60.
2) Don't bother choosing a scope. Instead enter a value of "1" for
the scope magnification.
3) Now enter the camera's focal length (the box directly below the
scope's focal length). I'll assume 500mm for this example.
4) Click the "Calculate Digiscoping Data" button.
5) Now scroll down a bit so you can see the Distance to Subject
estimator. Since you want to determine the distance required to fill
the frame vertically, enter in "2048" for the "Pixel Dimension of the
Object" box. 2048 is how many vertical pixels that the D60 has.
6) You want a 4 inch bird to fit in that vertical space, so we'll
enter 0.1 in the "Dimension of Object" box. 0.1 is 100 mm which is
approximately 4 inches. (25.4 * 4 = 101.6mm if you want to be more
precise).
7) The result is 3.01 meters or around 10 feet.
Now you can plug in the values of a digiscoping setup. Using your
102mm Mak with a 40mm eyepiece and a CP4500 at 18mm focal length, this
works out to 11.1 meters or well over 30 feet.
I originally put this part of the calculator in so that distances
could be estimated after the image was taken. But I guess it can be
used this way as well.
Jay Turberville
www.jayandwanda.com
