The Daylight Viewfinder app shrinks the live camera image down to a size that fits under the eyepiece, and the eyepiece blocks out the surrounding light. The eyepiece also magnifies and focuses the image. Even though the resolution of the live image you see is reduced, Apple's Retina display enables you to still get a great view of what you are taking a picture of. Above left is a screen capture of the iPhone's display showing what was seen through the viewfinder when the picture of Mt. Hood on the above right was taken.
Do you have purchasing preferences? Daylight Viewfinder is available for purchase through this web site, via many resellers, and also through Amazon.com.