Going RhinoCam™ One or Two Better....

I'm a Pentax guy meaning that, after some careful comparison, I decided to make my first DSLR a Pentax. The Number One reason was that Pentax has historically made their cameras backwards compatible with their lenses. In other words, I can put on my K-5 II body lenses from the Pz-1p autofocus film days (Pentax-F and Pentax-FA lenses). I can also put any of their K-Mount lenses (Pentax-A, Pentax-M, or SMC K). I can even, with a no-optical element adapter, use the superb Pentax Takumar lenses or other m42 screwmount lenses (of which there are MANY).

This was important to me because when I bought my first DSLR, I did not foresee being able to afford many of the $500+ autofocus lenses that were currently being offered on the *new* market. But I knew that I would want to play around with different lenses and this would be an inexpensive way to do it. I was right.

Along the way, I have accumulated a lot of various Pentax film camera kits, which were usually purchased for the lenses. I even decided one day to purchase a well-regarded Pentax 6x7 lens, the 165mm f2.8. With it came a hunk of junk that was formerly one of the original Pentax 6x7 bodies (no mirror lock-up) and a dented, but functional, prism finder.

With thoughts of the Fotodiox RhinoCam™ rattling around in my head, my eyes fell upon this neglected workhorse, in a box in my basement.

And that's when I realized that I was looking at almost all of the key pieces that I would need to build a Better-than-RhinoCam™, something that I will call the Pentax HippoCam (she's a wide body, baybee!)

My Pentax HippoCam (on paper) offers several advantages over the FotoDiox RhinoCam™:

For starters, I'm building around lenses and mounts made for a 6x7 image circle, not just 6x6 (same as for a 6x4.5). In addition, the Pentax 6x7 (or 67) lenses are quite a bargain. I already owned the aforementioned 165mm f2.8 and a 200mm f4. With my interest being wide panoramas, similar to what one would get on a Hasselblad Xpan™ (only digital), I purchased the well-regarded SMC 6x7 55mm f4. This lens has a reasonable size and weight and uses the fairly common 77mm filter size (which I already use on my Sigma EX 10-20mm f4-5.6). It also has a horizontal field of view of 65 degrees on a 6x7 negative size, which is equivalent to a 28mm on a 35mm film camera (or a 18mm on a Pentax APS-C sensored DSLR). We'll see if we can get it to throw an even larger image circle if unconstrained by the traditional 6x7 body.

The 6x7 body has the body size of the lens mount. It also has the 6x7 ground glass/focusing screen that I can use (like Fotodiox does ) for composing the shot. (Focusing is done while viewing through the camera, not the ground glass). I may be able to go Fotodiox one better and make use of the Pentax 6x7 prism finder (which would allow me to forego the use of a dark cloth for composing the shot).

The Pentax 6x7 is a great design choice also because you have a generous 80mm (!) flange to film/sensor distance. Fotodiox had to use a mirrorless camera like the NEX7 because their multi-manufacturer adapter on the front size eats up a lot of the flange to film/sensor distance, so they must use a thin camera. They can't abide anything with an overshooting prism or grip (like my K-5 II has). I'm designing my Pentax HippoCam to work with my K-5 II, but it will also work with the mirrorless K-01, which has the exact same flange to sensor distance. (My wife owns a K-01, so I will be able to use either - with her permission). 

I'm not sure what the dimensions are for the Mamiya RB system, but this would be another relatively inexpensive system with a huge flange to film dimension. If you already own Mamiya 67 lenses, you can apply most of my ideas with your parts... you'll just need to adjust the dimensions.

More to come, regarding the design objectives and the what the HippoCam will accomplish.