This is a performance analysis and review article of the FujiFilm Fujinon XF 35mm F1.4.
You hardly understand the specific differences in how the lenses work and how their performance differs from each other, do you?
Even if you look it up in magazines or on the Internet, all you will find are similar "word-of-mouth recommendations" and articles like that.
In this blog, while researching the history of lenses and their historical background, we estimate lens design performance based on patent information and actual shooting examples, and analyze lens performance in detail from a technical viewpoint through simulations.
Professional lens designer Jin Takayama will carefully unravel optical characteristics such as optical path diagrams and aberrations, which are generally not visible, and explain the taste and descriptive performance of lenses in a deep and gentle manner.
Now, please enjoy the special information that you can read only on this blog in the world.
The XF35mm F1.4 was released in 2012 as a standard lens for the FujiFilm X Series cameras.
The X Series uses an APS size imaging device, so the focal length is equivalent to 53 mm when converted to full size, and the Fno is 1.4, making it a so-called standard lens.
It is a large aperture standard lens for APS size mirrorless, but I think it is surprisingly few specifications for other companies. For example, SONY does not have a lens of E 35 mm F1.8 with a little dark Fno and F1.4 specifications.
It seems that there are only a few standard large diameter lenses for mirrorless use. This is a lens that will be an interesting subject for analysis.
In the previous article, we featured the large aperture medium telephoto XF56mm F1.2 as an analysis of the lens for APS for the first time in this blog. Please refer to the following link for details.
This time, in commemoration of the second round of analysis of lenses for APS, I would like to recall a little what "APS film" was.
APS Film was created in 1996 through a tie-up between film and camera manufacturers. Behind the formulation of the standard, there seems to be a thick drama involving the intentions of each company.
At the time of release, I was already a great camera and was knee-deep in the lens swamp, so I expected this APS film standard to "fail."
The first reason is that APS film is one size smaller than 135 film (full size), so it is inevitable that the image quality will decrease. The reason is that those who want high image quality do not buy APS film.
It may be difficult to understand in the modern era when digital cameras with more than 20 million pixels are common, so I will supplement the resolution problem a little.
In modern digital cameras, there is no difference in practical resolution between APS size and full size. The evolution of the image sensor (CMOS) has increased the number of pixels too much, so there is no difference in practical category.
Then, on the contrary, I will convert the film to the number of pixels of the digital camera.
It is difficult to express the resolution of the film as if it were a digital camera. However, the resolution of a full-size ISO100 film is approximately 8 million pixels, so the APS, which has a small area, shrinks by approximately 66% to approximately 5 million pixels.
The resolution of ISO400 film is much lower than that of APS film, so you can feel that the resolution of APS film is slightly lower than that of APS film.
The second reason was that the rise of digital cameras was foreseeable.
In 1994, before the advent of APS film, the first commercially successful consumer digital camera, the CASIO QV-10, was released, marking the beginning of the digital camera era.
It started at a time when we could foresee the arrival of the digital camera age in the future, so we could predict that the end would be early.
However, contrary to my expectation, it was a hit as a compact camera.
However, I wonder if it was until around 2002 that he was able to breathe for a while. When the number of pixels in digital cameras began to exceed 2 million, the situation reversed and APS fell.
Under such circumstances, a culture was born in which the sensor size for a digital single eye was expressed by comparing it to an APS film. As a result, only the mysterious expression of APS size remains in the world today.
Since single-lens digital cameras were becoming affordable around 2005, it is difficult to judge whether the APS film, which maintained its standard for about 10 years, was a success or a failure.
It is said that the sale of APS film was quietly ended in 2012.
I knew that the patent document itself was WO2013/088701, but I think I will adopt Example 2 this time, although the reproducibility of the data is poor in Example 1, which looks similar, and the cross-sectional shape looks slightly different.
I will omit the detailed reason, but it is because the design date of the analysis software OpTalix I am using and FujiFilm are not compatible.
Now, Example 2 is reproduced below as a design value.
The following design values have been selected and reproduced from the appropriate patent literature and do not correspond to the actual product. Naturally, the data is not guaranteed, and I am not responsible for any accidents or damages that may occur by using this data.
Analysis of Design Values
Optical Path Diagram
The optical path of the FujiFilm XF35F 1.4 is shown above.
It uses 8 lenses in 6 groups and 1 aspherical lens.
The first to third lenses on the subject side retain the typical Gaussian lens feel, but the fourth and subsequent lenses have a unique arrangement.
Three lenses are attached to the image sensor side. The number of lenses to which three lenses are attached has decreased in recent years.
In the past, until around the 1970s, coating technology had not been developed, so we used to design the type of lenses that could be attached even by force.
In the era when there was no coating, it was important in design to prevent irregular reflection on the lens surface by bonding lenses together to reduce the number of air contact surfaces.
The reason for this is that reflection occurs at the contact surface between the lens and air, reducing the amount of light reaching the film and darkening the effective Fno.
It was also intended to suppress the degradation of image quality caused by flare due to irregularly reflected light.
By the way, if you apply a coating, the irregular reflection on the lens surface will be greatly reduced (to about 1/10).
Because of this, coating technology has developed in the modern era, and the process of bonding three sheets together is only used when the aberration correction effect is extremely high, so it is becoming rare.
In recent years, super-resolution type 50 mm f / 1.4 lenses, represented by SIGMA, have been on the rise. This FujiFilm XF35mm lens seems to be an attempt to optimize the size of the product while taking advantage of the symmetrical arrangement.
Let's take a closer look at each aberration analysis section to see what kind of balance was aimed at as the standard lens for FujiFilm.
Graphs of spherical aberration, image surface curvature, and distortion
There is a little eerie undulation at the base of the spherical aberration graph, but the absolute value is kept very small.
Looking at the spherical aberration, it seems to be about half compared with the traditional and small symmetrical Gauss type lens, but it seems to be less than that compared with the SIGMA 50 mm F1.4 which is representative of the modern large high-performance lens.
You can see that it was aiming for somewhere between the traditional soft Gauss description and the high resolution. As a standard lens for the X camera system, it was also important to reduce the size of the entire lens.
In the past, this blog analyzed the NIKON 50 mm F1.4D as a typical Gaussian type analysis, and the SIGMA 50 mm F1.4 as a recent high-performance type analysis, so please refer to the following link.
The field curvature also seems to be well corrected compared to the traditional double gauss.
The distortion of the general Gaussian type has a residual correction of about minus 2%, but this lens has been corrected to almost zero level.
The reason why the distortion of the general Gaussian type cannot be zero is due to the restriction that the back focus must be lengthened in order to secure the space to place the mirror.
Since this XF35mm is a mirrorless lens, there is no need to stretch the back focus, so the degree of freedom of distortion correction has increased, so it can be corrected to the zero level.
Lateral Chromatic Aberration (Magnification Chromatic Aberration)
The Lateral Chromatic Aberrations is not an abnormal level, but it is slightly large for the number of components. The Lateral Chromatic Aberrations is an aberration that can be corrected by image processing, so it may be an idea to suppress it by image processing.
(Left)Tangential direction, (Right)Sagittal direction
Let's look at it as lateral aberration.
"Compared with the general Gaussian type, the aberration is considerably reduced, but in the open Fno, the coma aberration remains, and it seems that the design retains a slight flavor."
Spot Scale 0.3 (Standard)
The results of the optical simulation will be shown from here, but let's look at the spot diagram first.
Compared to the traditional Gauss type, it has been corrected moderately, but there is no feeling of excess like the SIGMA Art series, and it gives a good impression.
Spot Scale 0.1 (Detail)
Maximum Aperture F F1.4
Finally, let's look at the results of the MTF simulation.
It is a modern lens, and aspherical lenses are also used, so if you compare it with a traditional Gauss lens, you can see that the mountain is high enough even in the periphery.
As expected, it is disadvantageous when compared with the giant gun type such as SIGMA, but it is also important to consider the product size as a standard lens.
Small Aperture F4.0
With the open Fno, the performance was a little lacking, but if you narrow it down to the F4.0, you will be able to see how the resolution goes up.
You can enjoy controlling the aberration with this lens.
It was an interesting product to see how it was designed as a standard lens for the FujiFilm X Series, but I could clearly see that the APS size was fully utilized by balancing the size and performance at an intermediate point.
Example photos are in preparation.
If you are looking for analysis information on other lenses, please refer to the table of contents page here.