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Cosina cosinon-w ( Petri ) 28mm F2 MC

Reviews Views Date of last review
8 54,351 Fri June 8, 2018
Recommended By Average Price Average User Rating
88% of reviewers $123.57 9.00
Cosina cosinon-w ( Petri ) 28mm F2 MC

Cosina cosinon-w ( Petri ) 28mm F2 MC
Cosina cosinon-w ( Petri ) 28mm F2 MC
Cosina cosinon-w ( Petri ) 28mm F2 MC
Cosina cosinon-w ( Petri ) 28mm F2 MC
Cosina cosinon-w ( Petri ) 28mm F2 MC
Cosina cosinon-w ( Petri ) 28mm F2 MC

Fast wide angle, made by Cosina,who marketed it as a Cosinon-W (pics 3, 4). Also sold as a Petri.
Black anodised k-bayonet is indicative of early PK mount transition from M42 ie mid 1970's, but also can be found with standard bare metal PK mount.
Black, all metal, pentax k bayonet.

Focal length: 28mm
Max length: 37,6mm + mount
Max diameter: 62,5mm
Weight: ~140g
Aperture: f/2 - f/16, 6 blades
Min. focus distance: ~0.30m
Filter diameter: 49mm
Mount Type: Pentax K
Price History:

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Sort Reviews by: Date | Author | Rating | Recommendation | Likes (Descending) Showing Reviews 1-8 of 8
New Member

Registered: June, 2018
Posts: 1
Lens Review Date: June 8, 2018 I can recommend this lens: Yes | Price: $150.00 | Rating: 10 

Pros: sharp
Cons: expensive
Sharpness: 10    Aberrations: 9    Bokeh: 10    Handling: 9    Value: 9    Camera Used: pentax k3   

this lens is great.
my favorite lens.
There are also very good results in filmed cameras
New Member

Registered: January, 2018
Location: Paris
Posts: 8
Lens Review Date: February 23, 2018 I can recommend this lens: No | Price: $140.00 | Rating: 6 

Pros: Sharp above f4, nice colors
Cons: Blurry until F4, very far from a very good 28mm to my taste
Sharpness: 6    Aberrations: 7    Bokeh: 7    Handling: 7    Value: 5    Camera Used: K1   

Got a mint copy
Maybe a lemon (but not sure...) mine was not sharp until reach F4

F5,6 to F8 are very good except the corners
Nice Colors.
The problem is at this aperture I already have a tak 35/3.5 and a k28mm/3.5 which are far ahead of this one...

Overrated lens for me. Itís not the fast lens i hope. Poor result until F4. Not usable to my taste

Very good lens for 50/60Ä If you have not the choice....
Much better choice in Pentax SMC for IQ and build

Nota : don,t think monkey pic behind has been taken at f2 at speed 1/400(+nervous bokeh) ...f4 maybe or more

maybe this lens becomes a stellar one in apsc ....
New Member

Registered: October, 2016
Posts: 2
Lens Review Date: October 20, 2016 I can recommend this lens: Yes | Price: $90.00 | Rating: 9 

Pros: Great bokeh, very sharp, pretty small
Cons: CAs and Flares in a few situations
Sharpness: 10    Aberrations: 7    Bokeh: 10    Handling: 10    Value: 10    Camera Used: MX, Canon 550d   

I really love this lens. It is small, fast and sharp. Colors are no pro and no con for me, mine doesn't produce pictures with much contrast, but it doesn't look bad either. The only thing that is not so good about this lens is its behavior in situations where you shoot against the light.

By the way, I have the "MC COSINON-W" version of this lens, not the petri one. I don't know if there is much difference.

On crop this was the lens i used for everything. On film its pretty wide but you still are able to get some nice Bokeh. Anyway, the pictures may be better at showing you why I like the lens (All shot on a Canon 550d with minor postprocessing)

@2.8 (I think)



Veteran Member

Registered: May, 2015
Location: Black Isle, Scotland
Posts: 405
Lens Review Date: September 26, 2015 I can recommend this lens: Yes | Price: $70.00 | Rating: 8 

Pros: Cheap, vibrancy, decent sharpness when used right, wild OoF effect
Cons: Whole stop aperture ring, build, difficult sharpness, wild OoF effect, CA

You may have noticed that I've given this lens a high overall rating, but lower for everything else; this is because the lens is more than the sum of its parts.

First off, I've no idea why but when I got it the auto-aperture wouldn't function either side of F5.6-8. I took apart the mount and put it back together, not really having any idea what I was doing and losing a screw in the process. Now the aperture works, but as a preset. This doesn't really inspire confidence in the build quality, but hey-ho, I paid only £40 for a 28mm F2 so what can be expected? Like the other Petri lenses I own, the aperture ring also only does full stops.

Perhaps having something to do with my bungled mount job, the lens also judders when I take photos with it. I think this has occasionally thrown my focus off, and means it tends to work best in Live View, or with the 2s timer.

Edge sharpness is pretty dire until stopped down to F8, but then it's pretty fine - on the crop sensor at least. Centre sharpness is surprisingly good all the way from F2 until diffraction sets in. Though of course the centre is sharper at F5.6, you're splitting hairs unless trying to print larger than A4.

Flare resistance is minimal, so in most circumstances a hood is highly recommended. There is also noticeable chroma at high contrast edges, though we do have the modern advantage of software CA correction.

So why would I rate this lens 8/10? Sounds pretty crap, right? Yeah, but now we're coming to the good bits.

The standout quality of this lens is the colour. I was utterly astounded by how vibrant the colours, and particularly the reds, were. When flare is under control there is absolutely no requirement to boost saturation in RAW development. It's damn beautiful and satisfying to see.

The second aspect of this lens that I enjoy is perhaps a bit more of a divisive issue. Despite the standard aperture design (6 flat blades) meaning that bokeh has no character most of the time, when wide open the OoF effect is utterly wild. I have so much fun pointing this lens at different textures and seeing what comes out the rear end.

Without further ado, pictures!

Sharpness at F8


Out of focus

A flawed beast, to be sure, but a fun ride when tamed.
Inactive Account

Registered: February, 2012
Posts: 1
Lens Review Date: August 5, 2014 I can recommend this lens: Yes | Price: $145.00 | Rating: 9 

Pros: Sharp from F2 on, good color rendering, best 28mm Ive had.
Cons: build is not so good as pentax k lenses.

When I noticed that someone was selling this lens earlier this months I decided to buy it, I already got the famous Pentax K 35mm F3.5 but I was just very curious about this nearly ultra rare lens. In terms of sharpness this is really an outstanding lens, much better than my other 28mm's (pentax a 28mm f2.8, pentax m 28mm f2.9, panagor 24mm f2.5, sigma mini wide, and the vivitar 28mm f2.8), colors are great too. If you see one, just buy it I'd say.

Some images:

Image at F2

Image at F4

Image at F5.6

Image at F8
Senior Member

Registered: March, 2011
Location: Ontario
Posts: 115
Lens Review Date: January 17, 2012 I can recommend this lens: Yes | Price: $120.00 | Rating: 10 

Pros: Sharp, great colours, smooth focus and bokeh
Cons: Manual - K or M like

I think this lens is well suited for darker situations, being f2, and at that opening, it is still quite sharp. The bokeh transitions smoothly without any unsightly bright rims on lights/specular reflections in the background. Colors are rendered vibrantly.
As stated in an earlier review, the screw head nearest the locking slot, had to be covered with aluminum tape in order to allow the green button to work properly on my Kx.
I did a bit of research beforehand and found that this lens was made for Petri by Cosina (Cosinon). There were a few other 28/2's available in a K mount in this price range by Vivitar (Kiron/Kino) but these were reviewed to be soft when wide open so I went after the Petri and I am not disappointed.
This lens will be used frequently and is highly recommended.
Senior Member

Registered: February, 2011
Location: Tallinn
Posts: 162
Lens Review Date: April 2, 2011 I can recommend this lens: Yes | Price: $150.00 | Rating: 10 

Pros: beautiful sharp at f2 with creamy bokeh
Cons: it may not mount properly on K-5

So I got this lens out of curiosity and 'cos I got it cheap. I got it for 40EUR, but it sells on eBay sometimes around 150USD or more.
It really is exiting lens. Beautiful soft bokeh but pixel sharp in detail still.
Look at the pictures here
Initially I had difficulties to get the aperture lever to work on K-5. I could not understand what caused the aperture not close when mirror goes up. It works perfect on K10D.
When you look at the mount there is a screw close to the lock slot. It locates right under the contacts of the camera and one of contacts will "fall" right in the screw hole. Thus making no connection. When I placed a piece of aluminum tape over the screw hole it works as it should.
Lens Review Date: November 23, 2010 I can recommend this lens: Yes | Price: None indicated | Rating: 10 

Pros: sharp and high contrast at all apertures
Cons: none

tiis is the best 28mm lens i have ever used i used it on my k. 20d in custom permitted mode, i t was a gift from a lady at our photo club, who had gone over to canon from film. i could not believe my luck when i ran some tests, on tripod and hand held, its equivelent to42 mm on my sensor so it would serve as a short normal lens, i will probably use it for architecture details, i remember the petri cameras from the late 60s and early 70s the lenses were always well rated in photo mags but i never actually used one, then the brand dissapeared.
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