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Message: <blockquote data-quote="BF Hammer" data-source="post: 777809" data-attributes="member: 48483">I dug up this article about the differences between TTL, D-TTL, and iTTL and how the CLS fits in to it. The very dumbed-down version is that CLS communicates exposure data from camera to the flash. A SB-24 does not have the programming inside to understand that, which is why it either will only fire full blast or must have a lower flash power set manually. No optical or radio trigger can make the speedlight understand that data, but they can be made to pass the data to a speedlight that does have the smarts (like an SB-800, SB-600...). The older TTL standard just has the camera itself trigger on the speedlight at the main pin, and one of the other pins is the turn-off when the meter in the camera determines there is enough exposure. It is this simple system that is not compatible with DSLR camera bodies.<a href="https://www.scantips.com/lights/ttl.html" target="_blank">https://www.scantips.com/lights/ttl.html</a> On that note, I say it is a bit weird that older TTL cannot be made to work on DSLR because my Coolpix 995 from 2001 did use TTL speedlights in TTL mode with a bracket adapter. It was more like a thyristor setup with an external light sensor on the pop-up flash to estimate the power and I guess with no interchangeable lenses it can be done.</blockquote>