OK I am trying to find out what is going on with my flash when I use it at night in a poorly lite Football game. I have a Canon 1D Mark IV using a Canon 70-200 F2.8 VS 2 lens with a Yongnuo YN686EX-RT flash and a Canon cable. Now for Camera settings 1st photo unedited low res JPEG 1250 ISO F2.8 1/300 flash "2nd curtain" on ETTL 2nd photo taken a few moments later at 1000 ISO F2.8 1/300. I was shooting at 8K ISO "10K ISO with out flash" F2.8 1/1000 and the flash on ETTL and the flash was so weak I decided to try these crazy settings. Now with all that being said when I go to a well lite field and shoot 4000 ISO F2.8 1/1000 and ETTL I have zero issues at all.