As light enters the camera, it hits the mirror, then gets reflected up to go through the pentaprism. It is ‘optical’ because what you see comes from the image that the camera sees. This developer (emphasis films and digital) seems quite keen to work with the pinhole community from my experience so you may want to check out the app and if you don't see your camera represented they may be willing to work with you to make your photography easier! If everything works out I'll buy the app and adapter and report back here to let people know how it works. The optical viewfinder is the part of the camera you look through when composing and taking a shot. If they get everything to work (and it sounds like they will), Focal Viewfinder might be a decent app to help with composing wide angle pinholes. So far I have only been able to find an equivalent as part of Liveview. I quickly found that the Fn1 button does not give the virtual horizon that I expected. They're testing how well it works in beta right now. Its been so long since I played with the D800 that I have forgotten what I had set up and what was default. Undaunted the developer ordered off of amazon a 0.4x clip on adapter for the iPhone lens which bumps the iPhones camera up to a little over 100 degrees (the lens adapter is quite reasonably priced, about $20ish off of amazon).
VIRTUAL VIEWFINDER FULL
The issue here is the iPhone cannot display a full view of what the titan will capture making the app useless for wide angle pinholes. Turns out an iPhone's camera has an angle of view of about 60 degrees, where the 72mm cone on the titan is around 97 degrees. They were remarkably receptive to the idea and within a few days got back to me saying they were adding it as a pre-set but ran into a snag with one of the cones for the titan. I got in touch with the developer of one such app named "Focal Viewfinder" and discussed if they could make a preset for my titan 4x5. Selection is one of the fundamental user interactions in virtual reality (VR) and 3D user interaction, and raycasting has been one of the most popular. After checking for myself, there doesn't seem to be too many apps out there, and some are spectacularly expensive. I had heard on a youtube video about Ilford's Harman titan pinhole that virtual viewfinders are out there for various phones. You can ballpark things but composing with a pinhole and composing with an SLR are two very different experiences. So after recently jumping into the world of pinhole photography I've come to the realization that it's very difficult to really figure out your composition.