Cosina (Cosinon) Cosina 50mm f2 Heritage

เรื่องราวของเลนส์

The Cosina Cosinon-S 50mm f/2 is a compact standard prime made by Cosina, a prolific Japanese optical manufacturer known for producing lenses under many house and third-party brand names. This particular optic was also sold rebadged as a Petri, and at least one example has surfaced under the Vivitar brand (noted with a higher serial number and slightly different internal construction, making infinity calibration harder). It was offered in Pentax K mount as an inexpensive kit-grade or budget standard lens. No established nicknames or community jargon (such as 'Bokeh King' or similar) are evidenced in the available reviews. Its cult appeal is entirely practical and value-driven: reviewers repeatedly note how cheap it is to acquire (averaging around $7.50) and how easy it is to disassemble, service, rebuild, and recalibrate. A recurring caveat is the black anodised mount, which prevents electrical contact with Pentax DSLRs, so the green button and catch-in-focus may not work unless the user creates a contact (e.g. with foil or by removing a little anodising). Some users have gone as far as converting the lens, which involves removing the aperture lever and its protective shield.

สรุป: The Cosina Cosinon-S 50mm f/2 is a budget standard prime for tinkerers and value hunters. It is center sharp wide open, very sharp stopped down, and delivers pleasant (sometimes swirly) bokeh, all for a few dollars. Its easy serviceability makes it ideal for those who enjoy rebuilding vintage glass, though DSLR users must accept modifying the black anodised mount to regain electronic aids.

คาแรกเตอร์ของภาพ

โบเก้

ให้ภาพนุ่มนวลและเรียบ เมื่อเปิดรูรับแสงกว้างสุดจะเกิดเอฟเฟกต์โบเก้แบบหมุนวน (ซึ่งบางคนอาจไม่ชอบ) และได้รับคะแนนสูงจากผู้รีวิว

ความคม (เปิดสุด)

ตรงกลางภาพคมตั้งแต่เปิดรูรับแสงกว้างสุด; มุมภาพจะคมขึ้นเมื่อหรี่รูรับแสง และจะคมทั้งมุมถึงมุมที่ f/8 บนกล้องเซ็นเซอร์ APS‑C

แฟลร์

มักเกิดแฟลร์หรือ veiling flare (แสงฟุ้ง) เมื่อมีแหล่งแสงจ้าขณะใช้รูรับแสงกว้างสุด ซึ่งจะทำให้ความเปรียบต่าง (คอนทราสต์) ของภาพลดลง

คอนทราสต์

ให้คอนทราสต์ดีในสภาพปกติ แต่จะลดลงภายใต้แสงจ้าเมื่อถ่ายแบบเปิดรูรับแสงกว้างสุด

วิกเน็ตติ้ง

บนเซนเซอร์ APS-C ไม่พบการมืดมุม (vignetting) ที่มีนัยสำคัญ

รีวิวจากผู้ใช้

ข้อดี

Extremely cheap to acquire (average around $7.50) making it an outstanding value pick.
Easy to disassemble, rebuild, service, and calibrate infinity focus.
Center sharp wide open and totally sharp corners by F8 on APS-C.
Nice smooth bokeh, with high bokeh ratings from reviewers.
Fast enough f/2 aperture makes it quite easy to focus.
No significant vignetting or distortion on APS-C.

ข้อเสีย

Black anodised mount prevents electrical contact with Pentax DSLRs, so green button and catch-in-focus may not work without modification.
Contrast drops in strong light when shooting wide open.
Swirly bokeh wide open, which not all users appreciate.
Some branded variants (e.g. a higher-serial Vivitar version) have different construction that resists easy infinity calibration.
Anti-Pentax focus rotation direction (~250°) may annoy Pentax users.

เทคนิคการใช้

Stop down to around F8 for total corner-to-corner sharpness on APS-C.
Avoid strong direct light or use a hood when shooting wide open to preserve contrast.
If using on a Pentax DSLR, create a mount contact (foil or lightly removing anodising) to restore green button functionality.
Since these are easy to service, don't fear a hazy or stiff copy—rebuilding and recalibrating is straightforward on most versions.
Embrace or avoid the wide-open swirly bokeh depending on your taste.

แหล่งอ้างอิง (1)

Web-grounded synthesissecondary

The Cosina Cosinon-S 50mm f/2 is a compact standard prime made by Cosina, a prolific Japanese optical manufacturer known for producing lenses under many house and third-party brand names. This particular optic was also sold rebadged as a Petri, and at least one example has surfaced under the Vivitar brand (noted with a higher serial number and slightly different internal construction, making infinity calibration harder). It was offered in Pentax K mount as an inexpensive kit-grade or budget standard lens. No established nicknames or community jargon (such as 'Bokeh King' or similar) are evidenced in the available reviews. Its cult appeal is entirely practical and value-driven: reviewers repeatedly note how cheap it is to acquire (averaging around $7.50) and how easy it is to disassemble, service, rebuild, and recalibrate. A recurring caveat is the black anodised mount, which prevents electrical contact with Pentax DSLRs, so the green button and catch-in-focus may not work unless the user creates a contact (e.g. with foil or by removing a little anodising). Some users have gone as far as converting the lens, which involves removing the aperture lever and its protective shield.

https://www.pentaxforums.com/userreviews/cosina-cosinon-s-50-mm-1-2.htmlhttps://allphotolenses.com/lenses/item/c_745.htmlhttps://www.flickr.com/photos/tags/Cosinon%2050mm%20F2/https://www.dpreview.com/forums/thread/4238545