Blue asterisks are objects classified as stars from the WHDF data, red circles are everything else. The dashed lines indicate the expected offset given the difference between Sloan and UBRI (Johnson/Kron-Cousins). I don't have this value for the Z band.
This above is just for the original WHDF deep data, covering the central 7'x7' only. There is no Z-band for this data. It is compared with the SDSS Stripe 82 data.
The above is for the standard DR7 release (so not the deep stuff), but over the whole area of the extended WHDF. Haven't done Z for this one.
The above is for the SDSS Stripe 82 deep data, again over the whole area of the extended WHDF.