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Kowa Prominar 25mm f/1.8 MFT Lens Review

John Riley reviews the Kowa Prominar 25mm f/1.8 manual focus lens for Micro Four Thirds cameras.

|  Kowa Prominar 25mm f/1.8 in Interchangeable Lenses
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Handling and Features
SpecificationKowa Prominar 25mm F1,8 Front Oblique View

Kowa is indeed a venerable name in the world of photography, having produced many cameras and lenses from 1954 to 1978, plus more recently spotting scopes and even a range of ultra-telephoto lenses. The Prominar lens name has been used extensively and now we see it reappear in a series of three compact prime lenses for MFT format. Having looked at the Prominar 8.5mm f/2.8 (T3.0) and 12mm f/1.8 (T1.9) lenses, this time it's the turn of the 25mm f/1.8 (T1.9) – equivalent in 35mm-format terms to a 50mm f/1.8 standard lens. This is typically the lens that was supplied as standard on 35mm film SLRs over many decades. Let's see how it performs and whether there is still a place for the fast standard manual focus lens in the current digital world.

Kowa Prominar 25mm f/1.8 Handling and Features

Kowa Prominar 25mm F1,8 Top View With F Stops

The lens itself is quite compact in diameter, but fairly long. It weighs in at a solid 400g, which helps to convey a reassuring sense of quality. The finish is, as with its two siblings, impeccable. There is a 55mm filter thread and unfortunately this is needed for the screw-in lens hood provided. This is somewhat fiddly in practice, even though the thread is clearly of high quality. A bayonet fit would have been much more efficient.

The focusing ring has very sculpted and hard ribbing to ensure a good grip, helping to maintain the vintage look of the lens as a whole. The lens is manual focus only, down to 0.25m, just under 10 inches. This represents a maximum magnification of 0.15x, or 1:6.5. This is actually usefully closer than the average expectation for a lens of this type, which would be a magnification of 1:10. Manual focusing is very easy, particularly when using the various focusing aids available on the camera. For best results using the magnified image ensures accurate focus. There is narrow enough depth of field at 25mm and f/1.8 to ensure that the focus position is obvious. Without taking the camera from the eye, focusing can be achieved at f/1.8 and then the click stops counted down to set the desired working aperture. This seems to work quickly and effectively as the aperture set is fixed until altered. There is no electronic connection with the camera, so no automatic stopping down.

There is no depth of field scale, although there are ample distances marked in feet and metres to make this a useful possibility. 25mm on MFT format has a “35mm-format equivalent” of 50mm, and this is of course the traditional “standard” lens that many film photographers will have started off with. As such, designing it for high quality and a high level of correction is more or less a given. This focal length is looked on as a standard lens because it gives a view of the world similar to that of the human eye. It is suitable for a very wide range of subject matter and usually lenses of this type will take a fair amount of optical abuse from attachments, close up devices and so on, with quality holding well. The focusing and aperture rings move in the direction of Canon cameras, rather than Nikon/Pentax which move in the opposite way.

Finally we have the aperture ring, with a design that is very intelligent indeed. The review setting used was f/stops, which are provided with firm, positive click stops at full stop intervals, although one third stops are quite easy to approximate. Pressing a small button enables the whole ring to be rotated through 180 degrees to bring into play the T stop settings. The T stops, usually used for movie shooting, are clickless. The whole idea is highly inventive and works beautifully. There are 9 diaphragm blades, forming a nicely rounded aperture.

Kowa Prominar 25mm F1,8 On Lumix G6

Lens construction is 8 elements in 6 groups, including 1 aspherical and 1 XD (Extra Low Dispersion). This is fairly complex for the specification and bodes well for its performance.

Of course, there are a good many 25mm fast lenses available for MFT cameras, so let's see how that performance stacks up and if it could tempt the buyer into seriously looking at this option.

Kowa Prominar 25mm F1,8 Rear Oblique View

Kowa Prominar 25mm f/1.8 Performance

Central sharpness is very good at f/1.8 and excellent between f/2.8 and f/11. There is still very good sharpness at f/16.

The edges are very good from f/1.8 to f/2.8, excellent from f/4 to f/11 and again very good at f/16. Overall, there is a very satisfying crispness to images.

Kowa Prominar 25mm f/1.8 MTF Charts

How to read our MTF charts

The blue column represents readings from the centre of the picture frame at the various apertures and the green is from the edges.

The scale on the left side is an indication of actual image resolution as LW/PH and is described in detail above. The taller the column, the better the lens performance.

For this review, the lens was tested on a Panasonic Lumix G6 using Imatest.

CA (Chromatic Aberration) is commendably low both centre and edge and is unlikely to be a problem. If further correction is needed then there are software solutions, although for most of the time it will not be necessary.


Kowa Prominar 25mm f/1.8 Chromatic Aberration Charts

How to read our CA charts

Chromatic aberration (CA) is the lens' inability to focus on the sensor or film all colours of visible light at the same point. Severe chromatic aberration gives a noticeable fringing or a halo effect around sharp edges within the picture. It can be cured in software.

Apochromatic lenses have special lens elements (aspheric, extra-low dispersion etc) to minimize the problem, hence they usually cost more.

For this review, the lens was tested on a Panasonic Lumix G6 using Imatest.


Interestingly, Kowa provide a distortion figure and they quote -0.57% barrel distortion. The measured figure is -0.98%, which is still excellent. Again, further corrections can be made in software if desired.

Flare is generally well under control, with no signs of loss of contrast against the light. In the worst case scenario, with the sun in frame and at just the right angle, there will be obvious flare as in the sample image, but this is an extreme situation.

Bokeh, the quality of the out of focus areas, is super smooth, which seeing the rounded shape of the diaphragm is no surprise. This leads to very attractive looking images, which coupled with the high sharpness certainly have an overall feel that looks very, very good.

Kowa Prominar 25mm f/1.8 Sample Photos


Kowa Prominar 25mm f/1.8 Aperture range


Value For Money

The Kowa Prominar 25mm f/1.8 lens is priced at £599. There is a vast choice of alternative fast, bright 25mm lenses, including:

Panasonic Lumix G 25mm f/1.7 Asph, £148
Leica DG Summilux 25mm f/1.4 Asph, £459
Olympus M.Zuiko 25mm f/1.8, £299
Olympus M.Zuiko 25mm f/1.2 PRO, £1099
SLR Magic 25mm f/0.95, £552
Voigtlander 25mm f/0.95 Nokton II, £719
Meike 25mm f/0.95, £455
Zhongyi Mitakon 25mm f/0.95, £261

There is some powerful competition, and the Kowa lens, excellent though it is, is priced quite high in the overall field. Equally well, it is a classy performer, so the price point may be the only downside. For more options have a look at the Top 35 Best Micro Four Thirds Lenses.


Kowa Prominar 25mm f/1.8 Verdict

It would be difficult to argue against the usefulness of a 25mm fast lens on MFT format. As is true of any standard lens on any format, performance is very high and the focal length is very versatile.

The quality is not in question, but compared to a massive selection of alternative also very fine lenses the price does look high. This is especially true as the lens is manual focus. This leaves us looking very hard at the performance and general characteristics. For some, the price will not be an obstacle if the Kowa Prominar gives the desired “look” to the images. For others, there are a wide variety of choices, largely excellent as well in their various ways.

Kowa Prominar 25mm f/1.8 Pros

  • Excellent sharpness
  • Low distortion
  • Low CA
  • No flare in most circumstances
  • High quality of manufacture
  • Pleasant bokeh
  • ​Fast bright f/1.8 aperture

Kowa Prominar 25mm f/1.8 Cons

  • Manual focusing not for everyone
  • No weather resistance
  • No depth of field scale
  • Inconvenient screw thread lens hood
  • ​High price

Overall Verdict

Kowa Prominar 25mm f/1.8 Specifications

Lens Mounts
  • Panasonic Micro Four Thirds
  • Olympus Micro Four Thirds
Focal Length25mm
Angle of View50.2°
Max Aperturef/1.8
Min Aperturef/16
Filter Size52mm
35mm equivalent50mm
Internal focusingNo Data
Maximum magnification0.15x
Min Focus25cm
Box Contents
Box ContentsNo Data

View Full Product Details

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ChrisV Plus
13 2.3k 26 United Kingdom
3 Apr 2018 11:21AM

Quote:equivalent in 35mm-format terms to a 50mm f/1.8 standard lens

As usual, it seems it's fine to double the focal length, but not to add 2 stops to the aperture value. If it's 'equivalent' to a 50mm lens on 35mm format, it's also 'equivalent' to an f3.5. Exposure settings notwithstanding, that's what you're getting in terms of total light gathered and the effect on DoF.

The lens may perform reasonably well, but even by the standards of MfT, it's hard to see how this can be 4.5 stars and close to a recommendation. It looks [and controls by the looks of things] very much like my Voigtlander which actually is those two stops faster [it's quite a large heavy lens for the format]. In comparison to the reviewed lens the PanaLeica [which I also own] is smaller, lighter, considerably cheaper and of course, autofocus.

I'm wondering what a lens has to be in order for it to earn less than 4 stars? A hole at only one end perhaps?
3 Apr 2018 12:21PM
I think we all understand that different formats result in lenses that have different depths of field. There's little point in covering the same ground constantly, but hopefully the terms used are understood and clear. The whole point is that a 50mm lens on 35mm-format (full frame) is a standard lens as regards field of view. On MFT that will be the 25mm lens for the same FOV and that's what I'm referring to, and what other reviewers normally refer to as well.

As regards the last point, a lens has a rating that depends on how it is rated in several categories. There are very few bad lenses out there, but when there are we can be sure that they will receive whatever rating seems appropriate. Each star in the ratings covers a band of performance and lenses within a band will of course show some variation. It's a simple system intended as a guide and I haven't seen any system that is intrinsically better.
ChrisV Plus
13 2.3k 26 United Kingdom
3 Apr 2018 12:43PM
So there's no assessment based on price? Features? Weight? Not to mention comparison to other lenses within the same class? Might I humbly offer that those considerations along with performance [I assume you mean simply technically measurable aspects of IQ], might constitute a system that is intrinsically better. Not to mention more useful.

Yes we're covering the same ground again on the equivalence thing, but you explicitly stated not that this was equivalent FoV to a 50mm lens on 35mm format [which I have no argument with whatever], but that it was equivalent to a 50mm f1.8. You're using one half of the equivalence equation which is Fantasy Island - a place where one cake minus half a cake equals one cake.

MfT in particular [anyone reading should not I mainly use the format] likes to talk about equivalent focal lengths particularly when it comes to telephoto lenses when it makes it look like you're getting more in equivalence to larger formats. It's fine and logical to do that, but if you do, make a full comparison, not just the half that's flattering to the manufacturer, because that just defeats the object of any cross-format comparison [except for marketing purposes]..
3 Apr 2018 1:16PM
If you have a look at the review all these things are covered and ratings are summarised in four categories - Features, Handling, Performance and Value for Money. Then an overall rating is made, taking all these into consideration.
ChrisV Plus
13 2.3k 26 United Kingdom
3 Apr 2018 2:35PM
Ah yes - I note this lens does get 4/5 for 'features'. You may say that 80% worth of a lens' features are that it works like a lens [so no need for autofocus, camera controlled aperture or weather sealing], but that doesn't really leave a lot of room for differentiation does it? 90% for handling? Would it need to be defective to score less than a four?

I think I'm banging my head against a wall here, but it seems to me a lens would have to be a total stinker to score less than a four [what's the last time epz rated a lens so low?]

That would mean there's a very tiny band of differentiation in your scoring system. How helpful is that to your readers?
steveb127 2 1 United Kingdom
4 Apr 2018 6:35PM
I don't get why people are obsessed with “equivalence” – how does this camera and lens compare to traditional 35mm?

It can't be of any use to a beginner using say m4/3rds as if they couldn't understand the effects of cropping what's the likelihood that an understanding of 35mm equivalent is going to add value.

Surely by now most photographers know that if a sensor has a 2x crop size (Micro 4/3), you need to multiply the lens focal length by 2 to determine what 35mm lens it would be equivalent to in terms of FOV and a DOF. What is the benefit of that and to whom ? Why not learn how to use your equipment to the best of its abilities rather than in terms of some nebulous 35mm equivalent camera / lens combination ?

The obsession with equivalence has also created a deal of confusion - many who quote the crop multiplier also apply it to aperture directly eg: F2.0 m4/3rds is really F4.0 35 mm equivalence - wrong - for lenses F2 is F2 is F2 irrespective of sensor size.
ChrisV Plus
13 2.3k 26 United Kingdom
4 Apr 2018 10:23PM

The obsession with equivalence has also created a deal of confusion - many who quote the crop multiplier also apply it to aperture directly eg: F2.0 m4/3rds is really F4.0 35 mm equivalence - wrong - for lenses F2 is F2 is F2 irrespective of sensor size.

Right. But then 25mm is also always 25mm. You want to know what that means practically on a 4/3 sensor? It’s the same AoV as you’d get with a 50mm lens on a 35 format sensor. Sensible. You want to know what effect that has on DoF (which also conveniently equates to total light gathering). It’s 2 stops. Not complicated at all. No one is saying f2 is F4 - just that like 25mm equating to 50mm in effect, f2 equates to f4.

If you don’t want to make comparisons between formats, don’t make them. At all.

Other sites do this and it makes sense. I like this site- just not this aspect of it. It’s either slipshod or dishonest because it only tells half the story.

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