Waldo in South Carolina says:
Am I crazy or does shooting with a higher ISO result in sharper looking photos? I accidentally shot a house at ISO 640 instead of my usual 400 and I was surprised how good the photos looked. What causes this? I would have thought effect on sharpness would have been just the opposite.
Increasing ISO can allow you to shoot at a higher shutter speed or a smaller aperture either of which could make for a sharper image. If you are shooting on a solid tripod the higher shutter speed shouldn't make a difference but shooting with smaller aperture could be what you are seeing. Without knowing more details it's hard to tell exactly what is happening.
Traditionally, a higher ISO means grainer images but with today's DSLRs and mirrorless cameras, you can still get very good results at a high ISOs so don't be afraid to boost your ISO when needed.