Universal wide angle viewfinder V2 (large FOV, smaller image)

Another attempt to design a cheap and easy to make wide angle viewfinder for the Fat Shot 617 - Medium format 6x17 modular panoramic film camera, using widely avaliable parts. Less compact overall (longer but less wide and a bit heavier) but much more convenient than the previous version that I've made shortly before this one. It uses the same "wide angle 0.45x smartphone lens" as the source of the lens elements, but now it needs two of them.

Features

• Easy to source glass optics that are actually very good with sharp and clear image.

• Easy to print and easy to build design. No 3D printed threads and no supports needed.

• Lens positions are chosen so the visible image of the objects is almost the same distance from your eyes as the objects themselves. This means that your eyes almost don't need to refocus when looking through the viewfinder. And this is exactly what makes it very comfortable to use.

• Wide FOV that corresponds to about 20 mm equivalent focal length.

• Image size of about 23 degrees horizontally (same as a 18'' screen from 1 m away).

• Swappable masks to use with different lenses and formats. I've added 6x17 for 90 mm focal length and an empty slate for easier edits.

• Multiple mounting options.

Though there are a couple of drawbacks of this design, too:

• The main drawback is, of course, that it's pretty large (W = 54 mm, H = 53 mm, L = 58 mm, 87 g). As with the previous version, this should not be a problem for medium format, large format or other bulky cameras, but on smaller ones this viewfinder can look out of place.

• Parallax is present, but it's much less of a problem than in the v1 thanks to this VF long housing.

• Fish-eye distorsion is more noticeable on the smaller image.

Hardware

For this build you will need:

• Smartphone lens (see below) - x2.

• M3x12 screw - x5. Preferably use black screws.

And that's it.

The lens

The lens that is needed for its optics is sold mainly by the brand APEXEL (at least from what I see) and the images used by the sellers look something like this:

Be aware that there are even cheaper knockoffs out there with plastic lens elements that have slightly different dimensions and a bit harder to disassemble. This design is made for glass optics. To get the right lens pay attention to these details in user reviews:

• Both front and rear lens elements are held by metal threaded rings with visible notches for a lens wrench. Plastic version has press-fit plastic rings without notches.

• There is a nice center-pinch lens cap included. Plastic version has front and back push-on caps.

• On the front there is a M49x0.75 thread for a lens filter that is not present in the plastic version.

Here is how the correct version with glass elements should look:

And here it is fully disassembled:

Assembly

UPDATE 2025-01-19: The mounting system from V1 is not very good and kinda finnicky. I've added the version with an embedded shoe mount as an option. Use the files with "Embedded Shoe Mount" in the name instead of the original ones. It is not that flexible but much sturdier and easier to use.

Three lens elements from two of these lenses are needed for this build, one convex (front element) and two concave (rear elements).

Print one of each part and assemble everything in this order:

Notice that the concave lenses have flat surface on one side. These surfaces should be facing each other. Put both of them inside the rear part of the housing.

Masks are snap-on.

OLD MOUNTIING SYSTEM: There are two variants of the shoe mount adapter and both of them can be screwed two ways: on the front and on the back. Overall you have four options with a step of exactly 20 mm. Here is the image from the first version of this viewfinder. Same mounting solution is being used here:

But because it has such a long body, I don't expect the long adapter to ever be needed. For the Fat Shot 617 the 1st or 2nd option should be used (short adapter).