Well, well, well... Who would have thought that this small lens, would have such a big impact optically on a larger sensor camera like the Fujifilm GFX ?

I am quite astonished from the very first impressions so far.

Wide open aperture ƒ 3.5

Already at wide open aperture ƒ3.5 - the lens shows remarkably good resolution (sure, you have to spice it up a notch in Photoshop - since it is a 40 year old lens). But there it is, covering almost the entire GFX sensor being pretty sharp. The vignetting is unusual low. It is visible, but like a very soft, natural kind of slightly darker borders.

Super easy to correct !

Colors slightly subdued

So, you can punch it a bit with colors, in order to shine. I sometimes use the Fujifilm Velvia profile.

Very sharp !

Stop it down to ƒ5.6 or ƒ8 - and all vignetting disappears. Sharpness is top notch ! Everywhere !! Now that is really a remarkable lens.

WOW !

So, I have to agree with the guy who works at Cyberphoto, who wrote on his blog abuot the Sonnar 100/3.5 on GFX 100 - being an unusual good lens. I have not really read anyone else having written about that lens + camera combo on the internet.

Minimum focus distance: 1 meter

Is a bit on the long side with 100 cm. At the same time, it isn't that unusual that lenses around 90-100mm often have a min distance of 1 meter.

So, you will not get particularly close. Natural for most lenses from the 80s, the optical performance (sharpness) is slightly less - but the difference is minimal. You can still make beautiful images at 1 meter distance, at wide open aperture.

It's is small & beautifully crafted !

Another thing that puzzled me, are two things: the lens is smaller than I thought. Really compact !! And second; it is crafted in a beautiful classic style with high quality feeling.

Typical Carl Zeiss 1980s style.

Excellent & compact Travel lens

Since this 100 mm lens turns into a 80 mm lens on the Fujifilm GFX camera (due to it's wider image sensor). Making it an unusual compact (short) telephoto lens for travels ! The built-in Image Stabilization of the Fuji GFX 50s II works very well with this lens. So, the aperture of ƒ3.5 is not so much of a limitation really.

Lens hood recommended (Ø 55mm)

I do use a lens hood for the Sonnar T* 100/3.5, with a diameter of 55mm. It is a silver one which looks pretty weird. Well, I didn't have any other in that size and lengts, but will of course order simple black lens hood soon.

The kind of lens hood should be of the kind equivalent for a short tele photo lens of around 80mm focal length (give or take).

Notice: AEJ vs MMJ version

that there are two version of this lens; one produced in Germany (AEJ) I believe - while the latter was produced in Japan (MMJ). The issue with the AEJ version is that it produces "Ninja looking highlights" in the bokeh when stopping down the aperture.

I have the latter MMJ version. How to distinguish the latter version, is the aperture ƒ22 marking on the aperture ring is painted in green color.

Only 7070 examples were made

I read on the internet, that Carl Zeiss only made 7070 examples of the C/Y Sonnar T* 100/3.5 lens. Everyone was drooling over the much brighter, larger and far more expensive Planar T*100mm ƒ2.0 version. Which by the way isn't performing as well on the Fujifilm GFX compared to how the Sonnar T* 100/3.5 performs. Frankly spoken; I have no personal experience from the Carl Zeiss Planar T* 100/2 performance with the GFX.

Also other Contax lenses didn't fully perform as well like the Sonnar 100/3.5. I think next best in was the Sonnar 135/2.8 lens. The shorter lenses performed less well (as most wider lenses do on GFX) It's just what i read over the weeks about C/Y Contax lenses.

I guess the Sonnar 100/3.5 was (back in the days) considered to be a "bore" lens with film. Not particularly bright. But in terms of mediumformat.... ƒ3.5 isn't really strange. Several Fujifilm GF lenses start at ƒ3.5 such as the GF 30/3.5, as well the GF 50/3.5 pancake lens.

MTF Chart

However, the MTF charts from the Carl Zeiss Sonnar T* 100/3.5 lens shows rather evenly distributed resolution lines - all the way to the borders and corners. Which might explain why it even works well on the Fujifilm GFX camera with its larger sensor ? I don't know.

Notice that the third lines is for 40mm (micro resolution details), and not the commonly used 30mm. I think Carl Zeiss and Leica often show the 40mm line, while Canon, Sigma etc use 30mm resolution lines.

Remarkable resolution

So, when you look at the 40mm resolution line being located at level 0.6 when you use wide open aperture ƒ3.5 - is a remarkable good performance for a lens made in the 80s !! It then rises to level 0.7 / 40mm lines at aperture ƒ5.6

Now keep in mind that the MTF chart is a theoretical calculation, aimed at using analog film material, not a digital sensor combined with a whopping 3.24 mm cover glass thickness on top.

In practice

With a larger GFX sensor, you will still see a slight drop in sharpness at the borders when used at wide open aperture ƒ3.5 at infinity. It quickly gets sharper when stopped down to ƒ5.6 and gets critically sharp at ƒ8

Puzzling performance

It still puzzles me greatly - that such a small lens - from the 80s - would perform that well on a GFX camera.

I mean, given that the GFX cameras exhibit among the thickest sensor stacks with a total of 3.24 mm thickness made up in three layers... That does usually fuck up almost all vintage glass (even modern glass) used with the Fujifilm GFX camera (seen in a critical light, I mean).

Perhaps the SONNAR optical design itself contributes to the better performance on the GFX ?

Again; I don't know and can only speculate.