He used all kinds of films, formats, and cameras over his long career. Most of these specific films no longer exist. The rather famous inky black sky images often involved a red filter, neg intensification in one notable case, and plain ole heavy development. But since skies did not suffer from the same degree of high altitude jet contrails as today, even a deep yellow filter (what was termed a K2 back then) had a stronger effect darkening a "blue" sky than it typically does today. That high contrast crisp look tends to fall apart when those same old 8x10 negs are enlarged bigger than 20X24, or sometimes even bigger than 16X20. The mural sizes were printed softly, somewhat warm, and have a more poetic fell rather than dramatic flavor. I once split a big retrospective exhibition with the biggest collection of his mural sized images ever assembled, so got to see quite a few of those up close. His old grainy films and less precise optics simply didn't allow the same degree of detail as today. Later, his Hasselblad work was mainly done with Pan-X. He pretty much kept pace with camera advances, but his darkroom was comparatively primitive - not atypical for a pro commercial photographer, but hardly up to what commercial labs were equipped with.