Diy pentamirror blueprint

Baynatives wrote:

The plan is to put the mirrors in front of the lens and there won't be a viewfinder lens. That might mean I could eliminate the mirror that flips in an SLR because presumably the viewfinder lens also flips the image.

In the hundred plus years of large format cameras with ground glass and a black cloth over your head, I can't find any example of this. People always tolerated an upside down focusing screen. Hopefully that's just because they didn't want extra mirrors degrading the image and there aren't any technical reasons this won't work.

I decided this is physically impossible, or at least impractical and difficult to experiment. The lack of a viewfinder lens means one more image flip is removed. If I went from 3 mirrors to two, you would have to stand in front of the lens and block the view. Maybe 4 lenses would work but it's so convoluted.

Another issue is the viewfinder lens is much smaller than the capture lens, so each mirror is smaller but I want a full size image, so the ordinary pentaprism layout may not be valid. Each mirror would have to get larger and it would either not be geometrically possible or would be ridiculously bulky. I'm not certain but this definitely muddys the waters.

My solution is to make a mini camera obscura to view the image on a round table with the lens on the roof and a single mirror angling out to the landscape. But instead of walking into the camera, I cut a peep hole on the side of the roof so you can look down on the projected image. It's not as impressive but it works and you can put your cell phone camera on the peep hole to capture a cool shallow depth-of-field image and play with tilt/shift. Plus, the image is projected onto a nice solid white surface which looks a whole lot better than a ground glass translucent focusing screen. The ground glass always has a hot spot in the center when captured by a camera.

Here's my previous large format play camera where you can see the hot spot: https://www.flickr.com/photos/edgehill/albums/72157626735509238

Here's a camera obscura at our store that a friend built, if you aren't familiar: https://www.instagram.com/p/BvHtk-0hrJc/

One more thought: maybe the viewfinder lens doesn't flip anything. Eyeglasses don't flip the view. The peephole is much less impressive. Maybe a viewfinder lens in the peephole would make it more compelling? Definitely projecting onto a solid screen is more impressive compared to the translucent ground glass focusing screen but also having a big 16-inch image in front of your eyes is more impressive than peering through a peep hole.

I used to have an old super-8 movie projection screen from the 1950's which had millions of tiny glass beads glued to the surface of the canvas roll-up screen. That helped to brighten the image. Brightness is a big deal. That's why I think this is the right approach. OTOH, if I could get the pentaprism idea working, that would be awesome. I always like re-inventing the wheel!