Once you get into the census record on Ancestry.com, hold the control button down and click on the census record. A box should pop up with choices. Select "Add image to iphoto library".
Once you drag and drop it in Reunion, it will be small, but if you double click on the image, you'll then see a percentage number in the lower left corner of your image box. Click on that and a slider box will pop up which allows you to zoom in.
I hope this helps you. Let me know if you have any questions.