The question isn't precise enough...
It depends on the dimension and on the method :
If you measure a distance along Z (cmm axis) with the optics, it's not the same uncertainty than a Z dimension measured by contact, or a X/Y dimension measured by optics or by contact.
In your case, I would try to create a known artifact which represent the measurement, and qualify it with your method (for example, if you have to measure the distance between two holes on a thin part by optics, measure a standard part (not thin) with two holes by contact (on another cmm if you can), and then measure the part by optics, and compare the results...)
The question isn't precise enough...
It depends on the dimension and on the method :
If you measure a distance along Z (cmm axis) with the optics, it's not the same uncertainty than a Z dimension measured by contact, or a X/Y dimension measured by optics or by contact.
In your case, I would try to create a known artifact which represent the measurement, and qualify it with your method (for example, if you have to measure the distance between two holes on a thin part by optics, measure a standard part (not thin) with two holes by contact (on another cmm if you can), and then measure the part by optics, and compare the results...)
