My Contact and Test Sheets

From making my test sheet I made the assumption that 2.5 seconds was the right timing for all of my negatives. However when producing my contact sheet and , later on, my photos I realised that this wasn't the case. Whereas on some of my photos on the contact sheet 2.5 seconds was the right exposure time, other photos required a lot more time on a  higher aperture setting, and others required a lot less time on a lower aperture setting. For example, One of my photos required 2.5 seconds with an F8 aperture, (no filter), whereas another photo from my negatives required F11 at 4.0 seconds.
Because of this I needed to make test strips of each individual photo I was going to use. I made sure that I documented which photos needed what time by using 1.0 second intervals to determine what images needed what settings. 

I believe that the reason each photo needed different setting was because, on each photo to create a different effect the shutter speed was changed, because of this each photo was exposed to a different amount of light, thats why the aperture had to change.