Lenses We Love: Pentax 67 105mm f/2.4

Why Adapt Medium Format?

Flange focal distance is that magical measurement that lets lens adapters do their magic. As long as there's space between a lens and camera (while retraining infinity focus), Fotodiox is (quite literally) there to fill it. The Pentax 6x7 system has one of the longest flange focal distances of lens mounts we support, so our office's 105mm f/2.4 has been my holy grail of adapting.

Specialty adapters require a good amount of space between the lens and camera, depending on the relevant mechanisms involved, but medium format lenses make it so even DSLR systems (like the Canon EF and Nikon F) have access to premium options like TLT ROKR, DLX Stretch, and now RhinoCam Vertex.

What about crop factor?

When customers are new to adapting lenses, crop factor is always brought up in conversation. With a constant debate on the best formats (usually APS-C vs full-frame), Micro Four-Thirds and medium format complicate the discussion even further.

Creators who are used to the medium format fields of view are already in the habit of thinking of focal lengths differently. While a normal lens for a full-frame shooter is 50mm, 50mm is actually considered wide for medium format, and a normal lens for medium format is closer to 80mm.

Whether you're migrating systems completely or just interested in mounting medium format glass on your other cameras, cropping is almost always inevitable. As such, the focal lengths you've grown accustomed to are going to very different fields of views, thanks to the crop factor of the system you're adapting it to. Using the Pentax 6x7 system as an example:

• Full-frame: 89.64mm / 43.27mm = 2.07x crop factor
• APS-C: 89.64mm / 28.84 = 3.11x crop factor
• Micro Four-Thirds: 89.64mm / 21.64mm = 4.14x crop factor

When adapting our 105mm Pentax 6x7 lens, at the very minimum you are doubling the equivalent focal length, so our favorite 105mm will have the field of view of a full-frame 210mm. Yes, we could back up until we get the same framing, but it does affect our depth of field as well.

Can crop factor be reduced?

Focal reducers are similar to teleconverters. They both use internal glass elements, but instead of magnifying the image, they widen the field of view. Fotodiox doesn't offer any focal reducers, unfortunately.

The closest thing we can offer is our RhinoCam Vertex line of stitching adapters. They use larger image circles to create stitched images that net a wider field of view than a single capture. This also reduces the relative crop factor of the lens you're using. The unfortunate thing is that every RhinoCam Vertex does have a limit to how much area it can capture.

What if you used two RhinoCam Vertexes together?

The Test

It's an odd idea for sure. Though, on paper, it should at least be somewhat possible. The idea is to use a medium-format-to-full-frame RhinoCam Vertex in conjunction with a full-frame-to-APS-C Vertex. We figured our Fujifilm camera would be a good fit for the test.

One major issue we bumped into was that the tripod foot on our APS-C RhinoCam Vertex got in the way of mounting the two adapters together. We were fine once it was removed, of course.

As a quick refresher, the RhinoCam Vertex adapters require four total images: one in each of the corners of the image circle. There's enough overlap so that your post-processing program of choice has enough information to complete the stitch. For this test, I took a total of 16 images: in each of the four corners of the medium-format-to-full-frame RhinoCam Vertex, I'd take the four images needed for the full-frame-to-APS-C Vertex.

Results

To start off, here's a singular capture straight out the Fuji camera.

This picture has the expected 3.11x crop that we can anticipate for the Pentax 6x7 lens on our APS-C Fuji. After the 16 images, this is the stitched result:

For context, here's the equivalent capture area of the stitches for each RhinoCam Vertex format:

• Full-frame cameras: 47x46.9mm
• APS-C cameras: 30.4x30.4mm

This double-adapter solution that uses both in conjunction has a capture size of 55x54.7mm, so we did end up with a larger stitch than just the full-frame adapter by itself.