Ms-Optics ISM 50mm F1.0 GA

Review and Photo example of the ISM 50mm F1.0.

Gallery

The sample photo were taken with the Leica M-P typ240

Review

ISM 50mm F1 GA is a large-diameter standard lens from MS-Optics (Miyazaki Optical), and as the GA in the lens name indicates, it uses a Gaussian lens format. As the creator, Mr. Miyazaki, says, it is an extremely compact size and weight (180g) lens for a lens with F1.0 brightness.

The trade-off is that there is severe flare when the aperture is wide open, which makes it difficult to use as a large aperture lens becomes meaningless if you avoid opening the aperture and stop down. Also, with a wide open aperture of F1.0, it is difficult to focus on the desired position with double images on a rangefinder camera, so when I used this lens the most, I always had the EVF2 on my LEICA M-P. I used this lens on the LEICAS SL, and the high-resolution EVF called EyeRes was able to accurately determine focus.

Mirrorless cameras in the 2020s have EVF display performance that is satisfactory no matter which model you choose, so if you want to use this lens with emphasis on focus position, I think it is better to choose a camera with an EVF.
Personally, I feel that the previous large-diameter standard lens Sonnetar 50mm/F1.1 is more straightforward and easier to use when it comes to depictions at maximum aperture.

Since the lens has a large Gauss-shaped front element, a 55mm filter can be used to protect the front of the lens, but the lens side has an external thread unique to Ms-optics (general lenses do not have an internal thread). Please note that the filter is attached in the opposite direction than normal. The hood also has a 55mm internal thread, so it cannot be attached to a regular lens.

The sophisticated lens appearance can be said to be the achievement of Ms-optics.
There is a wide variety of colors, including the metallic green shown in the photo, metallic red, metallic blue, metallic brown (gold), black paint, black, and silver.

Specifications

Item	Value	note
focal length(mm)	51.5
Maximum aperture	1.05
Minimum aperture	16
Leaf blade	16
Lens configuration	5groups 7elements	Gauss-type
Minimum distance(m)	0.8
Lens length(mm)	41	Distance from mount flange to lens barrel tip (without hood)
Lens max diameter(mm)	54.7	The thickest part of the lens barrel
Filter diameter(mm)	55	Reverse mounting
Weight(g)	178

Reference links

Description of Double Gauss lenses by Wikipedia

Update

2024.3.15:Update
2024.2.11:Update
2022.01.11:First draft

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