The Android camera API allows the developer to turn off the pre-flash. The iOS Camera API does not have the option of using the flash without the pre-flash. We actually have an application requirement of trying to produce red-eye in portraits of children to screen for health problems. We have used the flashlight instead of the flash but it isn't as bright and does not result in red eye as consistently. Do you plan to implement a similar option (turn off pre-flash) in iOS?
Camera Flash Without Pre-Flash
I encourage you to file an enhancement request for this feature using the Feedback Assistant
Yes, please do. When you file your enhancement request, please include this write-up of the use-case you're hoping to enable, as well as what features you'd like to see in a manual flash control API. Thanks for the feedback!