SMC Pentax-M 1:4 20mm Asahi Opt. Co.

Cost: 0$ (average market price $273)

Another decent, impressively compact, lens from Pentax. This lens was owned by my girlfriend who use this lens in previous years on her Pentax K1000 (she uses a Nikon D800 now). So another favorite!

As most old Pentax lenses, it's good old quality with a solid metal build, and butter smooth focus and aperture. It has small profile, so combines well with the Sony a6000, even with an adapter. With the APS-C crop factor of 1.5 (resulting in 30mm), it still makes a decent landscape portrait lens. Good sharpness and color rendition, but as it is a slow lens, it is advised to use a tripod if you use a camera without stabilization such as the Sony a6000 (or shoot in bright light). The lens was more compact than its K predecessor.

The lens does seem to suffer from the "blue dot" caused by flare. I had a good bunch of pictures with this problem when photographing a sunset. So a hood might be advised.

Again proof that an old lens might still be worthwhile and compete with the latest lenses out there. I will definitely use this lens more often. Fully recommended and a pleasure to use!

To combat partial reflection, Pentax developed chemical coatings for the lens surfaces with minimum light loss. SMC is "a remarkable seven-layer lens coating process that cuts the reflection ratio down to just 0.2% per lens surface. The result is a dramatic improvement in both color fidelity and brightness and the elimination of flare and ghost images."
SMC was patented and first applied in 1971, when Pentax was still making screw mount equipment. The multi-coated lens lines changed from Takumar and Super-Takumar to Super-Multi-Coated Takumar and later on to SMC Takumar. SMC Pentax was used for the newly introduced K-mount lenses. Pentax's SMC is still today considered as one of the best lens coatings on the market.

  

Lens Specification:

Focal Length: 20mm
Maximum Aperture: F4
Minimum Aperture: F22
Image Format: 35mm
Lens Mount: Pentax K
Optics: 8 elements, 8 groups
Blades: 5 blades
Focussing: Manual
Minimum Focus: 25cm
Maximum Magnification: 0.12x
Filter Size: 49mm
Weight: 150g
Length: 29.5mm
Production: 1977 until 1984

Serial Number: 6847539

More information on Pentax

Samples:

More pictures will be added in the future...

Sources:
Wikipedia - Pentax
Pentax Forums

Update: Super-Takumar 1:1.8 / 55 Asahi Opt. Co.

Cost: 0$ (average market price $37)

This is one of my favorite lenses, so a must to add some more samples. This lens was passed on from my dad to me. He bought this lens before I was born and used it to take pictures of me as a newborn in the hospital. So I can truly state that this lens has been a life-long companion.

It is regarded as one of the best Takumar lenses made, possibly even from all Pentax lenses. I would state without to much doubt that it's within the 10 best.

The lens feel like good old quality. Not only is it a solid metal build, but is also butter smooth for focus and aperture. It's very small, so combines well with the Sony a6000, but looks ridiculously small on the A7II, even with an adapter. Especially with the adapter being wider then the lens. With the APS-C crop factor of 1.5 (resulting in 82.5mm), it makes an outstanding portrait lens and a good street photography lens on full frame. I like the extreme sharpness, beautiful color rendition and a very pleasing bokeh.

This single coated 55mm Takumar lens existed in minimum 8 different versions, based on the same optical diagram. The version tested here is the second version of the Super-Takumar and was manufactured until 1965. This version can be recognized on its fine ribs on the aperture ring and that the smallest F-stop (F16) is to the left on the ring. This was also the first Takumar lens where at least one of the glass elements was made from radioactive glass which yellows over time. The yellow tint of the lens helps achieve a very warm glow of the pictures.

I think this lens is underrated by much, and can still be found for a good price, even when adding an adapter. Fully recommended and a pleasure to use!

Takumar was Asahi's Optical's lens name, named after the Japanese-American portrait painter, Takuma Kajiwara, whose brother founded Asahi Optical. The Takumar name was used until 1975, when Asahi switched from the M42 screw mount to the bayonet K-mount. 

The Super-Takumar lenses include an early form of lens coating to prevent flare and a sophisticated stopping-down mechanism. A switch on the lens enabled "Auto" or "Manual" modes. 

The Takumar lenses have a good build, feel solid, and enjoy an excellent reputation amongst users, and are even quoted to be the best series of photographic lenses ever produced, equal or beyond the best, and more expensive German lenses.

Lens Specification:

Focal Length: 55mm
Maximum Aperture: F1.8
Minimum Aperture: F16
Image Format: 35mm
Lens Mount: M42
Optics: 6 elements, 5 groups
Blades: 6 blades
Focussing: Manual
Minimum Focus: 45cm
Maximum Magnification: 0.17x
Filter Size: 49mm
Weight: 215g
Length: 38mm
Production: 1962 until 1965

Serial Number: 1214904

More information on Pentax

Samples:

1/250 sec - ISO100 - Handheld

1/6400 sec - ISO100 - Handheld

1/2500 sec - ISO100 - Handheld

1/800 sec - ISO100 - Handheld

1/1000 sec - ISO100 - Handheld

1/500 sec - ISO100 - Handheld

1/640 sec - ISO100 - Handheld

1/3200 sec - ISO100 - Handheld

1/2500 sec - ISO100 - Handheld

1/1000 sec - ISO100 - Handheld

1/1600 sec - ISO100 - Handheld

1/400 sec - ISO100 - Handheld

Sources:
Wikipedia - Pentax
Wikipedia - Takumar
Pentax Forums
All Photo Lenses