I though these results deserved a thread of their own since many ask about TTL vs TTL/BL . I'll start off by saying that I agree with anyone who says you should first learn to master TTL flash since that may be your only option at some stage . But so far TTL/BL has proved to be superior "On my D40, 18-105mm and SB800" , I'm not saying 'yet' that it will be so on every system since TTL flash does exactly the same as TTL metering on my D40 . I'll start off by posting the results that surprised me most tonight , while taking a picture in the [dirty] mirror to see how my flash diffuser behaved I decided to compare the two systems just for fun . And just a few of the other 'exteme ' situation tests I've been doing - indoors , no ambient . In general , with my D40 , 18-105mm and SB800 , TTL flash has been as erratic as TTL metering in the camera while TTL/BL has been very consistent in its results . TTL/BL has fired weaker in bright light , as it is meant to do because it is designed to take the ambient [background lighting ] into account when it decides how much flash power to put out , and stronger with a white background indoors with little ambient . So far I would consider both of these scenarios to be superior to TTL flash [on the D40] . When the subject is indoors with the background further away TTL/BL fires slightly weaker . Once we zoom in to the subject they look very similar with TTL/BL being very slightly weaker .