A minor gripe with the preview steps.
When I see during the preview render that I need more or fewer steps, I need to type another value in the corresponding field (since I don't want to use the arrows to lower or add ten thousand of iterations). However, I have to be very careful then not to erase the first number of e.g. 50000 to change it to 60000, or the render will stop and restart all over (ruining the work already done, sometimes for hours). The same goes for lowering the amount: you have to first add a number to 50000, let's say 450000, and then isolate the 5 within the number and delete it to get to 40000.
Perhaps a delay in refreshing could be added, allowing for the typing of a new number in due time. Or an OK button could be needed before the system re-evaluates the number of steps. Or arrows per digit... Anyway, the goal would be to prevent the preview from starting all over inadvertently.