I have a flash that can light up the moon but this is not what I want. I am thinking that it is better to go for manual and doing some trial and error, or TTL and raising the iso?

Having said that, TTL might just get confused by the background darkness.

Advice anyone?
Hi Photoace! Sure, I did not know that.

So your advice would be that TTL is appropriate?

Would raising the ISO convince the flash to use less power?
Well, I knew that TTL meters the power of the flash by measuring how much light bounces off the subjects, but somehow I did not work out that the closest object would have such an effect.