There is no difference (in usage) between neg/slide loupe and GG focusing loupe, right?
Not really. It is nicer to have an adjustable loupe for GG.
Remember, the image appears on the lens side (or back side), of the GG.
So, in reality, you need a loupe that has, or can adjust, a proper focus point
beyond the surface of your GG, equal to the thickness of your GG.
A loupe for the light table basically focuses on the surface of the table,
not through the table glass, like a GG loupe needs to.
With all of this in mind, I found that a pair of drug store cheaters,
(reading glasses +2.50 or so), work fairly well for me. For more critical focusing, I wouldn't
recommend common, non-adjustable loupes having more then about 4X-6X power.
I have found the lower powered loupes make it easier to see the
image 'snap' on the dull-grain, or back side of the GG.
For me, with higher powered loupes, all I seem to see is the grain of the grind on the GG.
Also, drug store cheaters worked better for me then 'linen tester' loupes that some may suggest.
Marc