Hyperfocal distance on crop body

[jrader]

So I get how to do HFD focusing, but I was wondering if you should use the scale appropriate to the body that you are using? For example, say I use a 17-40 on a 30D (my current setup). The 30D has a 1.6x, so when I'm shooting at 17mm, do I use the numbers for 17mm or for 17*1.6=27mm (at whatever f#)?

My intuition says 27mm.

John

[argyle]

Use the value for the actual focal length, in this case 17mm...focal length is focal length, no matter which type of sensor is employed. The HFD for the crop sensor camera is accounted for by the appropriate CoC (circle of confusion) value that's embedded in the equation.

The HFD is calculated by dividing the square of the focal length by the product of the CoC times the f number. (focal length * focal length)/(aperture * CoC)

Oops...forgot to mention...the HFD value that's calculated by the above equation will be in millimeters...you'll need to divide the obtained value by 304.8 to convert into feet.

[jrader]

Much appreciation.

John