How do I avoid importing duplicates?

I am using iPhoto 9.6.1 on a 27" iMac running Yosemite 10.10.2.

I take photographs using a Nikon D810 which allows me to make 2 copies of each photo - one on SD card and another on a CF card. The photographs have the same name and file type (.jpg).

When I import the photos into my iMac, both copies import & then I have to manually delete half of them.

My Questions:

1) Does anyone know of a setting to avoid importing duplicates?

2) Does anyone know of a setting that would allow me to specify importing files from just one card in the camera?

3) If I have to import both copies, does anyone know of an efficient way to eliminate the duplicates, rather than manually?

I am trying to avoid removing the SD card each time, as this has led to corruption and loss of photographs in the past.

Thanks to the Mac community for your assistance.