Not sure how technically accurate this is... but... I have found to get the slide to fit the tv well you have to achieve a 1.33 ratio. That is the width divided by the height equals 1.33. I use the proportion of 11wx8.25h- I find that it fits the screen well and when manipulated a bit can be made to fit an 8x10 photo print with about a 1/2 inch to cut or add or whatever.
I am not sure if this is different of different size tv's however... my tv is a 32 inch if that makes any difference.
-Doris