Originally posted by atlnq9 o when your lens says 1:1 it means the image projected onto the sensor is the same size as the object being photographed.
That definition only accounts for 35mm cameras* technically APS-C cameras get an extra 1.5X magnification because of their smaller, higher resolution sensors. A full frame sensor would have a lens attached that is capable of focusing at 1.5:1 to achieve a similar effect, or have 1.5X the pixel density of the APS-C camera.
Originally posted by atlnq9 All I tried to say from the beginning was that the 100mm macro on apsc is the same as a longer focal length on FF
that assumption is incorrect, a 100mm lens is still a 100mm lens - no matter what format you put behind it. A 240mm lens on a 35mm camera would be considered a telephoto lens - but on an 8X10 format camera a 240mm lens behaves more like a 35mm lens - but it is still a 240mm lens. The only thing that is changing is the area of the image circle you are using from the lens.
*I have always been curious over whether the D-FA100mm f/2.8 WR macro is actually focusing at 1:1. Because on APS-C, 1:1.5 gives roughly the same magnification as 1:1 on a 35mm full frame camera and Pentax could have adjusted the optical design of the lens to account for the smaller DX sensor - hence the DA designation on the lens.