= Magnification
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<Magnification> compares an image's scale with a specified reference. <Transverse magnification> compares signed lengths in object and image planes; <angular magnification> compares viewing <angles> at an observer. Both are <dimensionless quantities>, but they answer different questions. A projected <real image> twice as tall has $|m|=2$; an <optical telescope>'s advertised viewing enlargement normally concerns <angular magnification>. https://openstax.org/books/university-physics-volume-3/pages/2-8-microscopes-and-telescopes[Ling, Sanny and Moebs, University Physics Volume 3, §2.8: Angular magnification and telescopes]{ref}.
Always specify the sign and the reference arrangement. For signed <transverse magnification>, $m<0$ means inverted and $m>0$ means upright; $|m|>1$ means enlarged and $0<|m|<1$ means reduced. A larger <virtual image> can subtend a modest viewing <angle> if it is farther away. At $u=f$, an ideal converging <thin lens> has no finite image height and hence no finite <transverse magnification>, while <angular magnification> can remain finite. Enlargement also does not guarantee extra detail: <diffraction-limited resolution> and <optical aberrations> limit the information available to enlarge. https://www.feynmanlectures.caltech.edu/I_27.html[Feynman, Leighton and Sands, §§27-6–27-7]{ref}.
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