The classic Watchmaker's Loupe Nr. 3*
*Everybody has different
Preferences
For their favorite magnification. I prefer rather large magnification and
thus will accept a smaller aperture. But everybody has a different preference.
Obviously the range of loupes commonly used is from Number 3 to 8. I sometimes
even use a Number 1 loupe, e.g. when oiling cap jewels.
Here is a table for the conversion of the Numbers of Loupes to Magnification (will confirm that shortly, because I fould not find a table on the web, but I guessed from the many pictures I saw):
| Number of Loupe | Magnification |
| 1 | 10 x |
| 1.5 | 6.6 x |
| 2 | 5 x |
| 2.5 | 4 x |
| 3 | 3.3 x |
| 4 | 2.5 x |
| 5 | 2 x |
| 6 | 1.6 x |
| 7 | 1.4 x |
| 8 | 1.25 x |
