Here's what I usually do, I hope I am doing this in the correct way....
if you check the camera, the raw image that you taken should be in 3504x 2336 pixels, if you need to crop certain images,make sure you "custom" the crop size(click n hold the crop tool and you will see" 4x6/5x7/etc" , and also "custom"...). Everytime I need to crop an image, I'd make sure the crop size is 3504x2336.I think that will keep the "original" size of the image that we are talking about.
I hope you get what I meant. and also, if I did this wrong, I hope someone can correct me and teach me to do it in the right way....
