Can anyone help me in understanding the settings on my simple flash gun? The head is extendable from "Wide 28" to "Tele 85" but I don't know what the numbers mean! There is a sliding switch for film ISO. The scale above the switch reads from 25-800 that I presume I set to whatever film I'm using. The scale on the switch shows what I think is the aperture settings. Below this there is a green dot and a red dot which I presume depends on what power setting I set on the front of the unit and whichever aperture the coloured dot lines up with is the aperture I use on the lens? Below that is a distance slider with 4 settings at the end (Tele, Std, Wide1, Wide 2) which I set to how I have the lens head and there is also a red and a green bar which I presume will show the range of the flash distance. However whenever I set all this to what I think should work & test it with the "Auto Check" the indicator doesn't light suggesting the scene isn't illuminated enough. Any suggestions please?