Kenko 400 Mirror Lens Review by Vladimir Zatsarin

Staff Blog

Kenko 400 Mirror Lens Review by Vladimir Zatsarin

Oct 26, 2017

“Mirror lens” is a special class of camera lenses with a construction similar to astronomical telescopes, which in their turn are a stand out in simplicity and reliability.
They have small dimensions combined with long focal length, light weight, a simple construction and are not expensive. That’s why lenses of this class are still quite popular.
The present-day lens of this class we will talk about is Kenko MIL TOL Reflex Lens 400mm F8.



Brief look

Appearance and first impressions


Brief look


Focal length




Angle of view






Minimum focusing distance


Lens construction

6 elements in 2 groups

Filter size








w/o lens hood and caps


with lens hood and caps

Without lens hood, caps and lens adapter this lens weighs 350g, but combined with its lens hood and caps the weight increases 1.5 times. This is due to the metal lens hood (more detailed below in this article).

Appearance and first impressions

400_mirror.jpgMirror lens construction

The optical system of Kenko MIL TOL 400mm F8 Reflex Lens consist of two mirrors, that result in more compact dimensions compared to classic optical lenses: this 400mm tele photo lens weighs less than 400g, while any equivalent lens with the same focal length made with traditional lens schemes will weigh several kilograms and have an impressive size that will require a special case or backpack to carry it.

The small number of lenses and mirrors in the construction allows getting rid of chromatic aberrations, which is a common issue for usual tele photo lenses. In order to suppress distortions, designers included in the construction an expensive ED (Extra-low Distortion) lens, but it significantly affects the price of the lens.

This lens is compact and lightweight, its body is in metal and almost covered with a wide rubber focus ring. Available in three colors: black, silver (the one tested) and white.

An important feature of Kenko MIL TOL 400mm F8 Reflex Lens is its compatibility with most of the digital DSLR and mirrorless cameras: this lens has a threaded T-mount and, with an appropriate adapters can be used with a variety of mount systems - Canon EOS, Nikon F, Pentax K, Sony Alpha, Sony NEX, Micro 4/3 etc. This review is made using Micro 4/3 camera with crop factor 2, therefore the angle of view becomes equivalent to 800mm lens on a full frame.

There is another interesting feature. In addition to the thread for the adapter, there is also a thread for filters with a small 30.5mm diameter that can be attached on the rear lens.

Something similar is made possible with the lens hood, too. The lens has a thread for 67mm filter size, and this thread can be also used to mount the metal hood (in the same way as filters). The hood itself has an internal grooving along the entire length (this is done to reduce lens flare). It also has a thread for screwing 77mm size filters.

400_adapter.jpgAn example of using the adapter for micro 4/3 system

400_thread.jpgThread for mount adapter and thread for 30.5mm filter size

400_hood.jpgMetal hood with internal grooving

400_focus.jpgThe focusing ring

The focus is manual and this is the standard for most mirror lenses (except the discontinued Sony SAL 500 f/8 Mirror lens). The depth of focus is small, so when focusing, it is recommended to use Live View and crop the desired focus area. The moving range of the focusing ring is wide (about 270 degrees) and smooth, therefore manual focusing is quite comfortable. The minimum focusing distance is 115 cm, so the magnification ratio is 1:2.5.

Another important characteristic of mirror lenses is the absence of the diaphragm. There is just a hole that cannot be closed or opened. This causes some restrictions as you can control exposure with the shutter speed and ISO only. However, the use of ND filters will mitigate these limitations.


A 400mm focal length is a lot, but a 800mm is a lot more! Let's try shooting from the same position with a standard lens and with Kenko MIL TOL Reflex Lens 400mm F8.


Kenko MIL TOL Reflex Lens 400mm F8 lens (equivalent focal length* 800mm)

400_tele_1.jpgStandard lens (equivalent focal length* 50mm)

* the equivalent focal length is a characteristic of the optical system that consist of a combination of a lens and a sensor that can give information about the angle of view of this system.

Using ultra tele photo lenses allows “squeezing” the foreground and background, thus taking unusual and interesting shots.

Playing with perspective

400_vista_1.jpg400_vista_2.jpg400_vista_3.jpg400_vista_5.jpg400_vista_4.jpgAlso the lens is suitable for shooting dynamic scenes.

Shooting of dynamic scenes


Long focal length and a relatively short minimum focus distance allow taking interesting macro shots.

The possibilities of macro photography



This lens is also perfect for shooting at large celestial objects.

400_astro_1.jpgSolar Eclipse

400_astro_2.jpgFull Moon


Kenko MIL TOL 400mm F8 Reflex Lens will be an interesting choice if you are looking for a budget friendly ultra tele photo lens.
Small dimensions, weight and relatively low price make it particularly attractive for travel shooting. Other strengths are its macro capabilities, the absence of chromatic distortion, specific bokeh and the possibility to combine it with most of the mount systems. When shooting handheld you need to control the shutter speed – it should be shorter than 1/400 — 1/800 sec. On the other hand, shooting with cameras equipped with a built-in image stabilizer will allow using slower shutter speed without loss of sharpness.

The downsides are its “manuality” and low speed. But miracles do not happen every day and, choosing an ultra super tele photo lens, you have to sacrifice something. Therefore, it is definitely not suitable for those fans of the "one push" photography.

In conclusion, Kenko MIL TOL 400mm F8 Reflex Lens is for experienced photographers who need a lightweight, compact ultra tele photo lens at an affordable price.

Vladimir Zatsarin
Vladimir Zatsarin @ Onfoto: