Fujifilm X-Mount & XF Lenses May Support Full Frame

Last Updated on 02/16/2015 by Chris Gampat

Editor’s Note: This is a syndicated blog post from John Caz. It is being republished here with permission and we found it to be quite interesting.

INTRO

Yes, you read that right but before fast scrolling through to the end, please read this blog post from start to finish. I am not affiliated with Fujifilm in any way, and I’m no optical engineer either, just a photographer with time on his hands to experiment and ponder on some questions that have been bothering me ever since comparing my Fujifilm X-T1 with my D800. Please journey with me on my quest to figure out if the X mount and X series lenses can support a larger sensor.

THE COMPARISONS / MY FIRST SURPRISE

When I first compared the Nikon full frame body with the X-T1, the first thing that intrigued me was the large size of the mount throat compared to the size of the sensor. That got me thinking, so I started comparing some bodies to see if i could get a better picture of what was really happening.

While looking at this comparison, we must not forget that the Nikon being a DSLR has the sensor further back from the mount so beware of miniaturizing perspective. Personally what I see is plenty of room for the Fuji sensor to grow. (Nikon F-mount 44mm, Flange to focal plane 46.5mm. Fujifilm X-mount 44mm, Flange to focal plane 17,7mm)

Looking at this comparison, we now have two mirrorless bodies with sensors that are nearly the same distance from the mount. This is even more promising to my eyes compared to the previous comparison with the Nikon. (Sony E-mount 46.1mm, Flange to focal plane 18mm. Fujifilm X-mount 44mm, Flange to focal plane 17,7mm)

This comparison is not very kind to Samsung. Looking at this and going over the table below with all the figures, one can only deduce that Samsung lenses are designed only to barely cover the APS-C format with no leeway for a future sensor size increase.

QUICK MOUNT SPECS

Full frame DSLR – Nikon F-mount 44mm, Flange to focal plane 46.5mm

Full frame Mirrorless – Sony E-mount 46.1mm, Flange to focal plane 18mm

APSC Mirrorless – Fujifilm X-mount 44mm, Flange to focal plane 17,7mm

APSC Mirrorless – Samsung NX-mount 42mm, Flange to focal plane 25,5mm

THE SCENARIO

So far this was just thoughts in my head and I knew that it was a far off scenario to even think that Fujifilm would design their mount from the start to be able to take a larger sensor. But then, if they did, this would be a very smart move indeed. But how was i to find out if such a theory could be true. Well the most obvious thing to do is find out what size was the rear projection of the X series lenses. As much as I searched, I couldn’t find any info, so I resorted to trying to figure out the sizes my self.

THE TEST INSTRUMENT

As I have already pointed out, I’m no optical engineer so my method of measuring the projection described below is certainly not precise nor may it be correct. What I decided to do is make a box out of cardboard that had a height of 17,5 – 18mm, cut a hole for the lens to slip into and place some white paper on the back to record the projection – pretty simple really.

This is my finished test instrument. It was originally the box that my Samsung phone come with. In the pic, I have the Samyang 12mm f/2 lens mounted.

THE TEST METHOD

Now I knew I wasn’t going to get any precise numbers, but I put in the effort to see and witness if there was any difference in the projection size of my Samyang lenses and the X series lenses. It goes without saying that the Samyang 12mm f/2 lens is specifically designed for the Olympus/Panasonic μ4/3 format but able to cover a maximum of the APSC format as well. So I knew that this would be my base on which to compare my X series lenses with. With the lights in the room turned off, I placed the lens on the white part of the my monitor (notepad) and just circled each projection for every lens I had at hand.

This pic of the projection circle is not a true representation of the real circle. This is because the test was done under a certain amount of light in the room which means that the fall off from the edges of the projection circle aren't visible unless I push the exposure later in post to reveal the extent of the projection circle. Another factor to consider is the thickness of the paper as well. — This pic of the projection circle is not a true representation of the real circle. This is because the test was done under a certain amount of light in the room which means that the fall off from the edges of the projection circle aren’t visible unless I push the exposure later in post to reveal the extent of the projection circle. Another factor to consider is the thickness of the paper as well.

THE RESULTS

The XF 56mm and the XF 23mm both gave me a result of 35-37mm. The XF 18-55mm at 18mm also was able to cover the 35-37mm range though just barely with obvious fall off at the edges. At 55mm the XF 18-55mm showed a much smaller circle around 30mm with fall off. The Samyang 12mm f/2 and the 8mm f/2.8 surprisingly showed a circle of only 18-23mm with heavy fall off. Wow, this was a true revelation, since up to this time I didn’t really expect to see much of a difference.
Now bear in mind the numbers above don’t really mean anything, since the paper-base of my crude test instrument is not precisely 17,7mm from the lens flange -though its pretty close. This test has more to do with the difference between the X series lenses and a lens that truly has been designed for the APS-C format. I could be wrong in my assumptions, so if you know better, then please leave a comment below and enlighten me, but this difference between the Samyang and Fujinon lenses is proof enough for me that the X-mount can handle a larger sensor. I’m not sure about a full frame, but I would bet that a 1.2x crop factor sensor would be a perfect match.

Here I have placed a piece of paper the same size as the full frame (36×24mm) sensor. The image circle I have drawn from the X series lenses is more than enough to cover the needs of the sensor.

Here I have placed a piece of paper the same size as the APS-C frame (24×16mm) sensor. The inner image circle I have drawn from the Samyang lenses is more than enough to cover the needs of the sensor.

One thing to also note is that due to the limitations of my testing which was done under a certain level of lighting and not under total darkness, the projection circles that I have created are smaller than the actual circles projected by each lens. Another factor to consider is the thickness of the paper which also absorbed a certain amount of light. This was especially noticed when I pushed or pulled the exposure while developing the pics of the projection circle images.

CROP FACTOR TABLE

1,0x14mm
18mm
23mm
35mm
56mm
60mm
90mm

1,2×16,8mm
21,6mm
27,6mm
42mm
67,2mm
72mm
108mm

1,3×18,2mm
23,4mm
29,9mm
45,5mm
72,8mm
78mm
117mm

1,52×21,28mm
27,36mm
34,96mm
53,2mm
85,12mm
91,2mm
136,8mm

LAST WORDS

Please note that all the above is speculation on my part based on some crude testing at home. It may or may not prove anything. I’m still recovering from the N3H2 virus which has hit me 3 times in the last couple months and doesn’t want to let go. So I’m open to your thoughts but please remember, it just me thinking out loud!