Optical Design value Analysis - NIKON AF-S NIKKOR 85mm F1.4G [No.039]

This is a performance analysis and review article of the NIKON AF-S NIKKOR 85mm F1.4G

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.

Overview

This lens is a large aperture medium telephoto lens of the G series, which is a high-grade lens for the F mount released in the early stage of full-size digital SLR cameras.

First, let's look at the history of Nikon's 85 mm F1.4 specification lenses.

• Ai Nikkor 85 mm F1.4S (1981) 5/7
• Ai AF Nikkor 85 mm F1.4D (IF) (1995) 8/9
• AF-S NIKKOR 85 mm F1.4G (2010) 9/10

*groups/elements

The 85 mm lens of the initial NIKKOR lens seems to have started from the Fno1.8, but the lens of the F1.4 specification will appear in 1981 as described in 1 item of the list above.

In the previous analysis article, we analyzed the Ai AF85mm F1.4D (2nd generation) described in the 2 items that evolved to auto focus support released in 1995.

I thought it was a lens with an old-fashioned taste, but it was an excellent lens leading to the modern 3 d hi-fi design.

The AF-S Nikkor 85 mm f / 1.4G (3rd generation) described in item 3 is the lens to be analyzed in this section.

Private Memoirs

As mentioned in the analysis article of the NIKKOR 50 mm F1.4G, the first full-size (FX format) NIKON D3 went on sale at the end of 2007, marking the start of full-size digital SLRs.

As for lenses, the G series was established for full-size digital cameras. This lens was also one of the G series and supported the beginning of the digital single lens system.

At the time of writing (2010), it has been 10 years since it was released, but it has been highly evaluated on the current bulletin board site and price site.

Personally, I still remember the PENTAX645D camera in 2010 when this lens was released. (Isn't it a NIKON product?)

Full Size The NIKON D3 did not come as a surprise, as it had been expected that single-lens cameras would one day be affordable for the general public. The PENTAX645D, however, was a medium-sized digital camera that was available at a reasonable price.

(In the end, I couldn't buy it, but. sadness)

I think it would be a good idea to deviate too much from the main subject, so let's turn the 645D topic to another occasion and go on to analyze NIKON's most popular telephoto lenses.

Document Survey

In this case, while the investigation of the second generation Ai AF85F 1.4D has been difficult, we found WO2011/108428, which seems to be the third generation patent. Now, assuming that Example 1 has been commercialized, the design data will be reproduced below.

Notes!

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 above diagram shows the optical path of the NIKON NIKKOR 85 mm F1.4G.

It has 9 groups of 10 lenses, and it seems that aspherical lenses and special glass materials are not used.

The fourth lens is thin and rough, but there seems to be no mistake as it is exactly the same shape on the official HP. It is a scary technology because it can maintain such a shape with high accuracy.

IF SOMEONE LIKE ME, WHO'S CLUMSY WITH MY HANDS, WERE TO TOUCH THIS FOURTH LENS, I WOULD BREAK IT IN AN INSTANT.

This cross section is also worth seeing.

The 1st to 3rd lenses at the front (left) are from the leading side of the Ernostar. The 3 pieces of the 4th to 6th lenses at the middle part are beautiful Triplet. The 7th to 10th lenses at the rear end are a variation of the Triplet with a concave junction.

It can be said that sticking to the traditional formal beauty is unique to NIKON.

Longitudinal Aberration

Graphs of spherical aberration, image surface curvature, and distortion

Spherical Aberration , Axial Chromatic Aberration

The spherical aberration is less than half that of the second generation Ai AF85F 1.4D.

Compared to the current product line, the axial chromatic aberration is a little left, but it is made with consideration to suppress the redness, and it seems that it will not stand out unless the shooting conditions are quite severe.

Field Curvature

The field curvature is also well corrected as well as the spherical aberration, and you can imagine that the image quality is uniform over the entire screen.

Compared to the second generation, the number of lenses has been increased by only 1, but it's amazing.

Distortion

A lens with this focal length is in a region where distortion is easily removed, and distortion is slightly negative (barrel shape), but it is not at a level that can be detected by shooting.

Lateral Chromatic Aberration (Magnification Chromatic Aberration)

Lateral chromatic aberrations was also corrected to about half compared to the second generation.

In the analysis of the second generation, lateral chromatic aberrations's incomplete correction remained as a cause for concern, but was that point greatly improved?

Transverse Aberrations

(Left)Tangential direction, (Right)Sagittal direction

Let's look at it as transverse aberrations.

It can be seen that coma aberration in the tangential direction is reduced by half compared to the second generation.

In the sagittal direction, it looks slightly worse than the second generation at around 18 mm in the peripheral part of the screen. However, the second generation has an abnormally small sagittal coma aberration for the large aperture of the F / 1.4, so the deterioration is only to the extent that each aberration is appropriately balanced.

Spot Diagram

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.

I thought that the spot shape after 18 mm from the periphery would be V-shaped due to the influence of the deterioration of the sagittal coma, but it does not seem to be at a level that bothers me.

As you can see in axial chromatic aberration, the chromatic aberration itself seems to remain a little, but the noticeable red side seems to be sufficiently corrected.

Spot Scale 0.1 (Detail)

MTF

Maximum Aperture F1.4

Finally, let's look at the results of the MTF simulation.

First, the performance at open Fno.

As for the MTF, the second generation lens is also excellent, so there is no big difference in the open Fno.

However, although the difference is small in the center, it can be seen that the flatness is improved in the periphery.

Small Aperture F4.0

A small aperture reduces aberrations and improves the MTF.

It must be the result of repeated improvements in spherical aberration, field curvature, and lateral chromatic aberrations. The performance improvement is more remarkable in the peripheral area.

Conclusion

Compared to the second generation Ai AF85F 1.4D, the number of lenses is only one more, but the performance balance is optimized as a whole, and it is designed to overcome weak points.

Also, the fact that "aspherical lenses are not used" cannot be overlooked as an excellent point as portrait lenses.

Using an aspherical lens is effective in correcting spherical aberration, etc., but on the other hand, there is a weakness that blurs the image.

Generally, it is called "Nenrin Boke" or "Onion Ring Boke", and the phenomenon that Tamaboke becomes rough and loses its smoothness is likely to appear.

In recent years, it seems that each company has been taking measures, but it is still the time when the bokeh taste has been sacrificed.

If an aspherical surface is used, the apparent performance, such as resolution and MTF, will be improved. However, the fact that "aspherical surfaces should not be used for portrait lenses where blurriness is important" is a lens that feels very Nikon.

Sample Picture

Example photos are in preparation.

If you are looking for analysis information on other lenses, please refer to the table of contents page here.