Samyang 135mm f/2.0 ED UMC Canon EF astronomical review

Astrophotography is a type of astronomical observation in which images of celestial objects are taken. For astrophotography, it is not necessary to use a telescope – a photographic lens can be used as an astrograph. However, such photographic lenses are subject to completely different requirements than for everyday photography – good sharpness across the entire field is required, as well as minimal distortion (aberrations) even when shooting with a fully open aperture. Accurate centering of the lenses in the lens is very important.

For rapid accumulation of light, a high aperture ratio is desirable. This is especially true for short summer nights.

Фотообъектив Samyang 135mm f/2.0 ED, установленный на зеркальную камеру Canon 550D.
Samyang 135mm f/2.0 ED photo lens mounted on a Canon 550Da DSLR camera.

One of the most important parameters of a photographic lens is the focal length. The longer the focal length, the larger the size of the object image on the photodetector. There is no such thing as magnification in astrophotography, since the size of the image on the screen may vary, as well as the distance from which the image is viewed. However, one can very roughly imagine 1x magnification as looking at a 10×15 cm photograph from a distance of about 30 cm, obtained using a 50 mm photo lens and a camera with an APS-C format matrix (about 25.1 x 16.7 mm). Then the angular size of the object in the image will coincide with the angular size of the object in the sky.

The 135mm focal length is quite unique for astrophotography. It seems that this is already more than 50…85 mm, but noticeably less than the focal length of small telescopes (from 400 mm or more). The main objects for a 135 mm lens and a camera with a matrix diagonal of 25…43 mm are large hydrogen, gas and dust, dark nebulae and other structures with a large angular size. At the same time, the 135 mm lens is not as heavy and bulky as fast photo lenses with a focal length of 200 mm, which allows it to be used when shooting with a mount with a small carrying capacity (for example, Sky-Watcher Star Adventurer).

Samyang 135mm f/2.0 ED на монтировке Sky-Watcher Star Adventurer.
Samyang 135mm f/2.0 ED on the Sky-Watcher Star Adventurer mount.

The hero of the review is the Korean Samyang 135mm f/2.0 ED UMC Canon EF photo lens. This is a telephoto lens with a focal length of 135 mm and f/2 aperture. Production of the lens began in 2015. The manufacturer has declared an optical design of 11 elements in 7 groups, including one ED element. There are no aspherical lenses. The lens is suitable for cameras with Canon EF and EF-S mounts, however, using a special adapter you can connect it to an astronomical camera, but this will require an additional mounting ring to install the photo lens on the mount. The field of view with a full-frame camera is 18.8°, with an APS-C camera it is 11.7°. The minimum focusing distance is 80 centimeters. There are versions of the lens for other mounts, but the lens for Canon EF is the most versatile due to its large working distance. It is for Canon EF, and not Canon EF-M, be careful! EF-M is another mount for Canon mirrorless cameras with a shorter flange.

Optical scheme Samyang 1352.0 ED
Optical design of the Samyang 135/2.0 ED lens

Samyang 135mm f/2.0 comes in a small cardboard box. Includes lens, hood, protective caps, instructions and warranty card. There is also a description of the characteristics on the other side of the box.

Box Samyang 1352.0 ED
Lens box

The lens does not have autofocus or image stabilization – they are simply not needed for astrophotography.

The Samyang 135mm f/2.0 ED UMC Canon EF lens body consists of metal and plastic. The focusing unit has a wide rubber ribbed ring. Focusing is smooth, but with a little friction – this is good, since the focus will not be lost with every touch. The focusing ring rotates 180 degrees, making focusing much easier. For comparison, the Canon EF 135/2L USM has 120 degrees. Weight is about 850 grams, length without hood is about 13 cm, with hood – 18 cm.

The input aperture is approximately 65mm. The reflections on the lenses are green, lilac and colorless. The front of the lens has a thread for a 77mm filter.

Передняя линза объектива Samyang 135mm f/2.0 ED. Диафрагма максимально зажата.
Front element of the Samyang 135mm f/2.0 ED lens. The diaphragm is maximally clamped.
Блок задних линз объектива Samyang 135mm f/2.0 ED.
Rear lens unit of the Samyang 135mm f/2.0 ED lens.
Юпитер-37А, Samyang 135mm f/2.0 ED.
Jupiter-37A (135 mm, f/3.5), Samyang 135mm f/2.0 ED.
Юпитер-37А (135 мм, f/3.5) , Samyang 135mm f/2.0 ED.
Jupiter-37A (135 mm, f/3.5), Samyang 135mm f/2.0 ED.

The lens hood is plastic, snaps into place with force, and holds securely. It is inconvenient to put on the protective cover with the hood installed; it is difficult for your fingers to catch on the protrusions.

Объектив с блендой.
Lens with lens hood.
Бленда установлена.
The lens hood is installed.

The body has a distance scale and a 9-blade aperture control ring. The lens focuses to infinity with a small margin. There are a total of 14 ring positions and 8 values (2, 2.8, 4, 5.6, 8, 11, 16, 22). The value switches with clicks. I didn’t like the aperture ring – it’s hard to tell what aperture is currently set. It also rotates too easily and can be accidentally turned, so be sure to check the position of the aperture ring before shooting.

The Samyang 135mm f/2.0 ED lens demonstrates excellent sharpness even from an open aperture – both in the center and in the field. It is very unusual to see such small stars throughout the field. The chromatism is corrected well, but not perfectly. Still, we should not forget that this is an f/2 lens with one ED glass. When using SLR cameras with the primary filter removed (“blue glass”), red halos around stars become more noticeable. This is especially noticeable when shooting through CLS or UHC filters, which have a gap between the red and green parts of the spectrum. With the L-Pro filter, ghosting is less noticeable. When shooting without filters, the lens performs very, very well.

When using astro-modified cameras or specialized astronomical cameras with a pixel of less than 5 microns, a noticeable drop in resolution is observed in the red channel at an open aperture. This leads to difficulties with focusing in the H-alpha hydrogen line. The star appears as a bright point surrounded by a small halo. You can focus all the light into a small circle, but its size will be larger than the previous option. I use a lens with a monochrome camera QHY5III178m (imx178, 2.4 micron pixel) – we can say that with such a pixel the lens works at its limit. Stopping down will improve the situation, but I prefer to sacrifice a little quality for the sake of greater aperture.

Examples of single frames with a Canon 550Da camera with a Marumi DHG Lens Protect 77 mm protective filter, without calibration at an open aperture (in-camera JPEG).
In RAW- at link.

Pictures with a Canon 550Da camera and a Svbony CLS Clip filter, which is installed between the lens and the camera (several focusing positions):

More test frames obtained through Canon 5D Mark II and Canon 550Da cameras, as well as comparison with the Jupiter-37A photo lens.

Samyang 135/2 + Canon 550Da
Samyang 135/2 + Canon 550Da
Yupiter-37A 135 mm f/3.5 + Canon 550Da
Yupiter-37A 135 mm f/3.5 + Canon 550Da

An example of an image with a ZWO ASI183MC color astronomical camera (2.4 µm pixel) after calibration, folding and processing:

M 8 “Lagoon” and M 20 “Trifid” nebulae, August 1, 2019
Nebulae M 8 “Lagoon” and M 20 “Trifid”, August 1, 2019.

An example of working with a QHY5III178m monochrome astronomical camera (2.4 µm pixel) and a Deepsky H-alpha 12 nm narrow-band filter after calibration, addition and processing:

Туманности Северная Америка и Пеликан, 3 августа 2018 года.
North America and Pelican Nebulae, August 3, 2018.

The lens has noticeable vignetting even on an APS-C sensor. The situation is completely corrected by calibration with flat frames.

The lens must be thermally stabilized before use, otherwise the focus point may change its position. Keep this in mind if you take the lens from a warm room to a cold one.

I recommend that you definitely buy a USB heating strip powered by an external battery to reduce the likelihood of the front lens or filter fogging up.

When shooting, I use the Marumi DHG Lens Protect 77 mm protective filter. It is always mounted on the lens and protects the front lens from dust and dew. When bright stars enter the frame, glare may occur.

Separately, I would like to say about the everyday use of the lens. At this focal length and aperture ratio, it is difficult to focus accurately without a focus confirmation chip. However, when in focus, the lens produces an image with excellent sharpness and pleasant background blur. Both Adobe Camera RAW and Adobe Lightroom have correction profiles for this lens.

When compared with the Jupiter-37A lens (135 mm, f3.5), at open apertures the Samyang 135/2.0 ED lens demonstrates undeniable superiority in sharpness, chromatism correction and aperture. Samyang allows you to collect approximately 3 times more light per unit of time than a similar 135/3.5 lens. This is especially useful when shooting on short summer nights, when you need to collect more signal in a short period of time.

Some pictures after calibration, stacking and processing, taken by me with Samyang 135mm f/2.0 ED and Canon 550Da:

Окрестности Антареса, 13 мая 2018 года.
Regions of Antares, May 13, 2018.
Witch Head Nebula, November 11, 2023
Witch Head Nebula, November 11, 2023
Andromeda Nebula, September 4, 2021
Andromeda Nebula, September 4, 2021
Звёздное скопление Плеяды, 6 декабря 2021 года
Pleiades star cluster, December 6, 2021
NGC 1499 California Nebula, January 04, 2024
NGC 1499 California Nebula, January 4, 2024
Veil Nebula, September 2, 2019.
Туманности М8 и М20, 13 мая 2018 года.
M8 and M20 Nebulae, May 13, 2018.
Кавказская горная обсерватория ГАИШ МГУ, 26 сентября 2022 года
KGO Observatory, September 26, 2022

+excellent sharpness even at open aperture
+smooth focusing with large ring travel
+good enlightenment
+low chromatism in the blue channel

-red halos around stars (spherochromatism)
-reduced resolution in the red channel, especially when working with small pixels (less than 4.3 µm)
– possible glare from bright stars
– inconvenient protective cover.

Despite the shortcomings, I really like the lens. In my opinion, this is the ideal lens for a lightweight mount like the Sky-Watcher Star Adventurer. I quickly got used to the high aperture – after shooting with the Samyang 135mm f/2.0 ED lens, even “fast” telescopes like the Sky-Watcher BKP150750 will seem very “dark”. Aperture is especially important on short summer nights, when you need to collect as much signal as possible in a short period of time.

The main competitors for the Samyang 135/2.0 ED are Zeiss 1352, Sigma 135/1.8 and Canon EF 135/2L. Zeiss is several times more expensive, but it may have higher on-axis sharpness and better chromatism correction. Sigma has autofocus, in terms of sharpness it is supposedly between Zeiss and Samyang, but it does have autofocus. The Canon EF 135/2L is autofocus, but its sharpness and chromatism correction are the worst. You can compare the sharpness of lenses using the service of website.

I would like to note that all photographic lenses MUST be tested before purchase (against the starry sky or an artificial star), since due to lens distortions there is a chance of getting optics that are unsuitable for astrophotography.

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