Suppose i want to make a Picture of a Tiger,in the National park or in wild life safari,and to fill in the Frame with my Aps-c Eos Camera with Focal Length at 300mm,how close or far i need to Approach the subject,I would Like to Know the Distance in meters or in Foots Roughly?
There are many species of tigers and they vary in size. Suppose that the tiger in mind is a male Bengal tiger. They have an avarage nose-to-tail length of 270 to 310 cm.
Using a 300 mm lens on an Canon APS-C camera will give you a horizontal angle-of-view of about 4.3 degrees. To fill the frame with a subject measuring 3 meters horizontally you'd have to stand 40 meters away. Depending of how you want to frame the shot you might have to move closer/further away.
There are many tools that you can use to calculate this distance available on the Internet. This one for example.