Macro pics - FF or APS-C

[witeken]

Due to (the image quality of FF, the 100mm L), and the ISO advantage, apparently FF is simply better, correct?

Actually, it's a bit more complicated.

Because of the bigger sensor (and thus higher focal length), you will need to take a smaller* aperture for the same DoF. Smaller aperture = need to take higher iso/lower shutter speed. But that's compensated by the bigger pixels, which give you better high-iso performance etc .     

*smaller= higher f-number. When the aperture you count in mm's (or whatever) is the same on 2 lenses, the DoF is always (actually, not always, there are other fysical variables...) the same. The purpose of the f-number is not to tell something about DoF, but about how fast the lens is.

Ummm...no, it's pixel density as stated, not sensor size.  Compare the 5DII to the 20D, FF and APS-C with the same pixel density - does the 20D have a 'magnification' advantage?  No.

It's about the raw magnification advantage. Not the advantage you get with post processing or digital zoom . It's obvious that a recent camera has a higher pixel density, better high-iso performance,... then a very old camera... Do you also compare computers of 1990 with computers you can buy today? No? 

[rj79in]

For a similarly framed shot, the APS-C will give you more room to work with as the FOV will be for a 160 mm lens. 100mm macro on an APS-C will be useful in certain specific situations.

[neuroanatomist]

Ummm...no, it's pixel density as stated, not sensor size.  Compare the 5DII to the 20D, FF and APS-C with the same pixel density - does the 20D have a 'magnification' advantage?  No.

It's about the raw magnification advantage. Not the advantage you get with post processing or digital zoom . It's obvious that a recent camera has a higher pixel density, better high-iso performance,... then a very old camera... Do you also compare computers of 1990 with computers you can buy today? No? 

There is NO real (i.e. optical) magnification advantage to APS-C. None. The 'advantage' is only due the usually higher pixel density of APS-C.  A lens will project an image onto the image plane, a FF sensor 'sees' a 36x24mm portion of that image circle, an APS-C sensor only 'sees' a 22x15mm portion of that same image circle.  So, at 1:1, the FF sensor can image a larger subject (e.g., almost a whole US quarter, while an APS-C sensor can't even capture a dime at 1:1).  In fact, 'digital zoom' is closer to the truth than 'raw magnification'. 

The 5DII vs. 20D is a convenient comparison because they have the same pixel density.  If you'd like to compare current cameras, I invite you to explain how the APS-C T3/1100D has a 'raw magnification advantage' over the FF Nikon D800.