photomicroscopically

The story

1. Proto-Indo-European*bʰeh₂-
2. Proto-Indo-European*bʰéh₂os
3. Proto-Hellenic*pʰáwos
4. Ancient Greekφᾰ́ος (phắos)
5. Ancient Greekφῶς (phôs)
6. Ancient Greekφωτο- (phōto-)
7. Englishphoto-
8. Proto-Indo-European*mey-der.?
9. Ancient Greekμῑκρός (mīkrós)
10. Proto-Indo-European*speḱ-
11. Proto-Indo-European*spéḱyeti
12. Proto-Hellenic*sképt͏̌omai
13. Ancient Greekσκέπτομαι (sképtomai)
14. Ancient Greekσκοπός (skopós)
15. Ancient Greekσκοπέω (skopéō)
16. Latinmīcroscopium
17. Italianmicroscopio
18. Englishmicroscope
19. Englishmicroscopic
20. Englishphotomicroscopic
21. Proto-Indo-European*h₂el-
22. Proto-Indo-European*h₂élisder.?
23. Proto-Indo-European*leyg-
24. Proto-Germanic*līką
25. English todayphotomicroscopically

From photomicroscopic + -ally.