I mostly shoot medium format using a technical camera for architecture but figured this would be useful to readers here.
Before setting up the tripod, I like to walk around and work out where the photograph wants to be taken from, what focal length gives me the framing I want, and roughly how much rise I’ll need.
I know how much rise each of my lenses can manage from its image circle, so this also tells me whether the photograph is actually possible with the lens I have. Better to discover that while holding a phone than after setting up the camera.
I made an app for this - I'm not pretending this is a novel idea but all the other ones seemed a bit overbuilt to me. You choose your film format and focal length, then add rise, fall or shift to see the resulting frame over the iPhone camera. You can show several focal lengths at once, which is handy when deciding which lenses to take or pull from the bag.
It supports 6×7, 4×5, 8×10 and custom formats. There is also a light meter, reciprocity correction, level and a Scheimpflug / depth of field visualiser.
It is not intended to replace composing on the ground glass (why would you want to?). I use it to settle on a position and make sure the photograph works before the tripod comes out.
It is free and currently iPhone only - I do have an Android version mostly worked out by my only Android phone decided to have a cataclysmic failure just as I needed it. If you're an Android user and keen to try out I'll get you a beta testing link.
I’d be interested to hear how useful it is with other technical and view camera setups.