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Cosina / Petri Cosinon-s 50mm F2

Reviews Views Date of last review
5 31,906 Mon June 1, 2015
Recommended By Average Price Average User Rating
80% of reviewers $7.75 7.20
Cosina / Petri Cosinon-s 50mm F2

Cosina / Petri Cosinon-s 50mm F2
Cosina / Petri Cosinon-s 50mm F2
Cosina / Petri Cosinon-s 50mm F2

Compact standard prime. Also sold as a Petri (pic 2).
Note that these typically have black anodised mounts, this means there won't be electrical contact with a pentax DSLR so green button may not work, nor will catch in focus. Solution is normally to create a contact with eg foil or by removing a little anodising off the lens mount.

aperture f2 to 16 with 7 stops.
6 blades.
49mm filter.
Min. Focus: 45 cm ~ 1,48 ft
Focus ~ 250 rotation, anti pentax.
Weight ~ 165g.
Mount Type: Pentax K
Price History:

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Veteran Member

Registered: May, 2015
Location: Black Isle, Scotland
Posts: 405

1 user found this helpful
Lens Review Date: June 1, 2015 I can recommend this lens: Yes | Price: $20.00 | Rating: 8 

Pros: Very cheap, creamy oof, great sharpness at F5.6-8, small
Cons: Poor close focus, whole stop aperture ring, no body aperture control


I bought this looking for the cheapest lens on evilBay that wasn't broken to use for Single in June 2015. Having used it for a month I feel more qualified to give it a review. My original is below, for what it's worth.

First of all, I do actually love this lens. It's limited, but it's also cheap and having spent a month using little else I often find myself angling to go back to it. I like the colours that it gives me, the microcontrast, its resistance to flare, and all of this is made that much sweeter by the fact that it was only 15 plus p&p. This also comes with a nice, smooth out-of-focus effect.

Objectively it is by no means a high quality lens. When my copy arrived the focus ring was a tad sticky (this is less of an issue in the heat, so probably just old grease), though with a nice throw nonetheless. The aperture range is only from F2-16, and in full-stop increments at that. It's quite poor at close range as well, managing only just less than 0.5m. Its sharpness range is nothing special; at reasonable magnification it is acceptable from 2.8-11 in the centre, and 8-11 at the edges. Peak centre sharpness appears to be at 5.6, so depending on the subject 5.6/8 will be the sweet spot. The bokeh is smooth rather than busy due to the slightly curved aperture blades. I've also found chromatic aberrations to be negligible at all apertures; even wide open you really have to push the contrast to pull them out. The inbuilt hood has proven very effective at eliminating flare. Significant vignetting wide open.

So all in all, if you haven't by now gotten yourself a 50mm prime and you're on a real shoestring budget then I heartily recommend this lens. If you're just looking to mess around with one of the cheapest lenses on the market then this is still a good shout. If neither of these apply then it's up to you really. To round off this review here are a few shots from my Single in June 2015 run.

non functioning links removed

Old review.

Picked this up deliberately searching evilBay for cheap lenses, and very happy with the purchase.

For such a bargain the wide-open sharpness is okay, but the real show-stealer is the silky smooth OoF effect. It's just a shame it can't focus terribly close, but that's what we have extension tubes for.

Photo was 'ere

I'm no expert so treat my scores with a handful of salt, though I stand by the 10/10 for value.
Senior Member

Registered: December, 2013
Posts: 223

1 user found this helpful
Lens Review Date: December 18, 2013 I can recommend this lens: Yes | Price: $1.00 | Rating: 8 

Pros: Light weight, quite sturdy, great price
Cons: focus to rapid, coma at wide apertures
Sharpness: 8    Aberrations: 6    Bokeh: 8    Handling: 6    Value: 10   

I've owned 3 of them, all of them needed infinity reset
on aps-c you get swirly bokah reminiscent of the Helios 44 between f2.8 and f5 (found out when i delicked one for video shooting on a canon SL1/100d) now its been used on a canon 5d mark 3 after i was finally convinced to trade it with a super takumar 50/1.4 with a serious fungal infection (every element completely webbed bar the radioactive one

one of my other copies had bubbles at the edges of the front element, needless to say this one was was sharper than my CZJ Tessar 50/2.8 @ f5.6 to f11

and my final copy survived a swim in the sea with a Pentax MV (RIP) but image quality is still alot better than most kit zoom lens

by the way the coating is non insistent on most copies you pickup today so use a hood

as for the price i got all of the lens for $1nzd
New Member

Registered: September, 2010
Location: Milano
Posts: 9

1 user found this helpful
Lens Review Date: April 28, 2011 I can recommend this lens: Yes | Price: None indicated | Rating: 7 

Pros: cheap, smooth focus ring, portable
Cons: too soft at f/2

I found this lens on my father's "old" Petri MF-101 and i had a couple of shots with it, but don't use it so much (I don't like 50mm on APS-C.

some pics with this lens:
New Member

Registered: April, 2011
Location: Worms DEU / Adelaide AU
Posts: 1
Lens Review Date: April 21, 2011 I can recommend this lens: Yes | Price: $4.00 | Rating: 7 

Pros: Cheap, Ok Sharp once stepped down, build quality
Cons: Quit soft at f2, none others for the price

It's a dirt cheap lens! Ok so you can't expect mega performance out of it.

For what it is its great, a fast 50mm build like a little tank! I personally have dropped mine more then 4-5 times on the tiles and not a single scratch on it.

As I mentioned above, its quiet soft at f2, starts getting sharp around 5.6 for me.

Bokeh its all right, little too much busy and not buttery smooth.

I butchered mine and have stopped it down to around f4 permanent So I can shot in Aperture Priority all the time.

Get it i would say and play with it, even if you can't find some use for it, it sure does look great in the cabinet

Veteran Member

Registered: October, 2010
Location: madrid
Posts: 833
Lens Review Date: December 4, 2010 I can recommend this lens: No | Price: $6.00 | Rating: 6 

Pros: Dirt cheap, sturdy, possible victim of modification:)
Cons: Quite soft till f/4

Buy it if you find it really cheap..then open it change optical elements to see what happens, make a pinhole lens or whatever(i'm planning to make a frankestein with it and maybe use the mount to make a pentax mount adaptator or mod it into another brand lens).

The lens is okay though, i got a couple of portraits i's fast enough..and from the signs on mine it's sturdy..mine has been abused and it still works fine..
The aperture ring seems to be made from cheap plastic..the rest seems to be metal and from the weight you can tell it's got glass inside.It starts to be sharp at f/4 and delivers best at f/8, in those settings the image quality is ok.
The softness at f/2 is bearable and the bokeh is fine.

Edit: most of what i dislike may come from the abuse my lens had suffered (i discovered myself looking upon it with some tenderness in it's last moments of life).

two portraits taken indoors at night:
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