What is the proper pronunciation?
There are some words in Chumash that depending on which Chumash you use there is either a patach or shva (for example צללו in אז ישיר).
What is the proper pronunciation for these words? It sounds more correct to say it with a shva but many Chumashim as well as the classic siddurim have it with a patach.
This is a very old difference of traditions amongst the baalei dikduk and mesorah.
Generally speaking (with some important exceptions) the sefardi custom is to write it as a shva and the Ashkenazi custom is that it is a chataf patach.
In actual pronunciation there is only a very slight difference, as it is not a full patach but rather a chataf patach which should be pronounced as something midway between a patach and a shva.
In fact, it has been argued that the purpose of chataf patach in these words is to highlight that its pronunciation should be like a shva na, since shva na would be pronounced in those circles similar to a patach. Now when it’s accepted to pronounce shva na closer to a segol, these words should pronounced similar to a segol, like a regular shva na.
ראה מנחת שי בראשית י”ב ג’, ושמות ט”ו י’, סידור ר’ שבתי מפרעמישלא באז ישיר בהפירוש בשם המהרש”ל, ספר המסלול במסילת הניקוד נתיב ד’ שביל כ”א, שו”ת יצחק ירנן ח”ד סי’ ט’, ועוד.