Novella where the protagonist is not powerful in their home universe, but is transported to Nazi Germany. Very sensitive to the eyeglasses taken from concentration camp. Power truly blooms when he sacrifices self at one point.
I read this story in 80s. Might have been new then but not certain. Longer than a short story & may have had sequels. I would especially like to find if they exist.
Barbara Hambly's The Magicians of Night, which is the second book in the Sun-Cross Series.
The two wizards, Jaldis and Rhion, had dared the dread Dark Well to answer the desperate call of a world without magic. Jaldis had not survived the dreadful Void. Now Rhion was alone in a world he could not imagine -- the world of Germany in 1940.
The four would-be wizards of the Occult Bureau welcomed him to their home in Schloss Torweg. They wanted his help desperately. But they would not heed his advice against the calling up of dark magic. They needed magic to overcome the enemies they claimed were trying to conquer their fatherland. To that high mission, nothing could be neglected, however dark and ugly.
The bit with the glasses:
The psychic impact was as if he'd unsuspectingly plunged his arm into acid. Yet at the same time what was in the box - the dim miasma floating over those neat, insectile frames and dust-covered lenses - was ephemeral, gone even as he jerked his hand out, sweating and gray-lipped and sick. He glanced quickly to see if von Rath and Weineke had noticed, but they were talking together, the SS doctor dimpling under the young mage's adroit courtesy as if his words were a glass of cognac. If she'd known how she would have smiled.
Hands shaking, sweat standing cold on his face, Rhion looked back at the box. For a moment it seemed to him that those flat, folded shapes of metal and glass were the skeletons of men, stacked like cordwood for burning, sunken eyes sealed shut and mouths opened in a congealed scream of uncomprehending despair.
And the equinox is when he can get home due to the surge in magic:
"And I don't want to find out. Or what you'd do with it after that. I never wanted to come to your world, or to have anything to do with your verkakte war. In any case, my only way out of Germany - my only way out of your world - lies at the Dancing Stones near Schloss Torweg. That's the only place the wizards in my world will know where to look for me, and tomorrow night, the night of the autumn equinox, is the only time when I'll be able to raise enough power to reach out to them and make the crossing. And that's where I'm going."
I previously provided it as the answer to Magician transported to our Earth and captured by Nazis, who learn magic from him
