autofocus : making the main page post images smaller

Hello,

I’m working with the autofocus theme and i made a modification so that each post on the main page is 800px wide and 175px high. I’m leaving the images i’m adding for my posts at it’s original resolution, which is somewhere around the ballpark of 3300×2400 pixels.

The images on the main page for each post are so big you can’t really make out what it is, or at least for my taste. Is there a way to make the image small so that you can make out more of what the image is ONLY for the main page images for posts?

here is my blog

https://www.beaucoupla.com/blog