I like to simulate different focal length and sensor size based on an image i have taken. I have a full frame body so I like to know how the picture would look like if I have taken with a cropped frame body. Also a different lens. For example, if I have a picture taken with a 200mm lens on a full frame body, I like to know how it would look like using a 400mm lens etc. Is there any software that I can use to simulate that effect? Possibly Photoshop and so how can I do that in Photoshop?
I know Nikon has a Lenses Simulator but I like to see with the image I have taken. The picture is just example and it isn't correctly cropped.