Technically this should be a part of my review of the C/P 25/1.4, but I couldn’t wait to share my latest observations with you, so here you go 
This is not a scientific comparison, nor has it the aim to be exhaustive – it is merely to show some of the differences between the two lenses under certain conditions. Those conditions are:
- Indoors setting with available light
- Close focusing for maximum bokeh
- Aperture wide open on each lens
What I want to compare here are the following points:
- Bokeh (i. e. rendering of out-of-focus areas)
- Optical qualities (vignetting, distortion, sharpness, colour)
- Speed
The setup I used for this comparison was pretty simple – in fact I simply shot away at a scene that happened to just be there by chance – a teapot and a salt shaker on our kitchen table, with some light reflections from kitchen stuff in the background. This proved to be a quite usable setting for checking the three above mentioned points.
Now without further ado, here are the resulting pictures. Click them each to view a larger version that also contains a 100% crop showing each lens’ sharpness performance.
First, the Lumix 20/1.7:
Olympus E-P1 + Lumix 20/1.7 @ f/1.7, 1/125 sec, ISO 200
And next, the Cosmicar/Pentax 25/1.4:
Olympus E-P1 + Cosmicar/Pentax 25/1.4 @ f/1.4, 1/125 sec, ISO 200
Right away I think it is worth noting that both lenses perform exactly the same in terms of speed. Both pictures were exposed for 1/125th of a second, and both are equally well exposed. This can only mean one thing, namely that the Cosmicar/Pentax’ maximum aperture setting, which is nominally 1.4, is in fact (only) a 1.7(*). It does show significantly more bokeh though, but this might at least in part be due to its greater focal length of 25mm vs. the Lumix’ 20mm.
Speaking of bokeh, I personally find that the C/P’s rendering of out-of-focus areas is much more pleasing. Not only does it offer more, it is also quite different from the Lumix’. The Lumix’ bokeh is – as most other aspects of the Lumix – very clinical. It is more of a consistent blur of things, with rather harsh transitions between in-focus and out-of-focus areas. The C/P, on the other hand, has a much more ‘alive’ bokeh. There seems to be action going on, the transitions are smoother – simply put, it has a certain magic to it that I find (Ashwin Rao might beg to differ here) the Lumix lacks – at least in this particular case.
As I said, the Lumix’ performance is quite clinical (to me). It is a great performer technically, as can be seen from the pictures: there’s only the slightest distortion (if at all), no vignetting worth mentioning, it’s sharp – it’s good. Whereas the Cosmicar/Pentax shows strong barrel distortion, it has vignetting at every aperture setting, it has terribly soft corners – but then again it wasn’t designed to be used with sensors larger than 1″, was it? But there are also areas where it performs better than the Lumix. First, it is sharper, at least in the center. Now before you shoot me for such heresy, let me say in my defence that I did not do a thorough sharpness comparison between the two. I know that the Lumix has a sweet spot somewhere around f/2.8-3.3 where its sharpness is stellar, but it is a tad soft wide open, which the C/P isn’t. You can see this in the 100% crops, although I have to admit it is a bit unfair since I autofocused with the Lumix and it didn’t hit exactly the same spot that I focused on with the C/P. But I can tell you from other pictures I took that it is sharper than the Lumix wide open.(**) The other aspect is color signature, which is a bit warmer with the C/P. I personally find that much more pleasing – in fact it always bugged me about the Lumix that it renders a bit too cool for my taste.
To sum it up: The Lumix is the better performer technically speaking, but I think this was to be expected (it does cost more than twice as what the C/P + adapter cost new, and it was designed for MFT). My personal impression though is that the Cosmicar/Pentax has a lot more character. Even with all its flaws it just gives the pictures a certain uniqueness, as if it were to say “I know I’m not perfect, but isn’t that what’s so loveable about me?” And that’s exactly it. I love the Cosmicar/Pentax 25/1.4 for how it renders – not so clinical, not so perfect, but with a certain charm of its own.
That’s why I do indeed prefer it over the Lumix as my everyday-walkaround-take-pictures-of-everything-in-any-situation lens, although the Lumix still has the advantage of autofocus, which might come in handy from time to time
*) I could secondarily verify these findings by pointing both lenses at the same well-lit scene, first wide open and then stopped town to f/2, 2.8 and 4. Both performed identically, giving 1/3200 sec. at their initial aperture setting, then 1/2000 @ f/2, 1/1000 @ f/2.8 and so forth.
**) dpreview Forums user madmaxmedia pointed out to me that there might be something wrong with my sharpness rating for the two lenses. So I did another test and I have to admit that this time the results contradict what I originally stated – the C/P is in fact not sharper than the Lumix wide open (I may have mistaken a crispy sharp shot from the C/P for having been taken with f/1.4, where it was in fact f/4!). But I find it is a close call, and the C/P does get really really sharp when stopped down, which is amazing for such a small lens. (Sharpness samples of the C/P will of course be included in my final review soon!)
So here are two 100% crops that show how each lens actually performs in terms of sharpness wide open, for you to compare (click the links to open each picture):
Cosmicar/Pentax 25/1.4 @ f/1.4 | Lumix 20/1.7 @ f/1.7
Buy the Pentax 25mm f/1.4 C-mount TV lens from B&H Photo Video Audio!
Buy the Panasonic Lumix G 20mm f/1.7 lens from B&H Photo Video Audio!
February 17th, 2010, 5:51 pm | 
Cosmicar/Pentax 25mm f/1.4- I love the bokeh and warm tones in the pics. Don’t mind the vignetting
Panasonic 20mm f/1.7- Sharp
Which lens should I get for my e-p1? I can’t decide
As mentioned in my email, I’d recommend the 20/1.7 for general shooting, as it is a dedicated Micro Four Thirds lens with full sensor coverage and autofocus, is bitingly sharp at any aperture and has a very versatile focal length. It’s also small and light and easy to carry around with an E-Px or GF1. The Pentax is really a specialty lens, and one might not want its unique signature in every picture. It has its charms of course, but I personally only use it every now and then, as it’s only sharp in the center and has no AF. But of course this is a matter of taste and preferences.
I have 3 C-mount lenses and 2 different C-mount to m4/3 adapters; none of these lenses fit into either of the adapters because the base of the lenses is too wide to go all the way into the “well” at the bottom of the adapter. You would have to file off the bottom corner of the lens, and I haven’t been brave enough to do that yet.
You don’t mention this problem, so I guess either the Pentax is skinnier than some, or your adapter is wider.
Do you know what brand your adapter is?
Yes, I’ve heard of that problem, and in some eBay auctions they mention it and recommend a certain type of adapter to use. The problem is of course that the C-mount has a shorter flange back distance, i.e. the lens needs to be closer to the sensor than a Micro Four Thirds lens. The C->MFT adapter thus has its base recessed into the MFT mount, thereby limiting the possible diameter of any lens to be mounted. The Pentax 25/1.4 is a very slim lens, so it should fit into virtually any adapter.
My adapter is from “Kipon” (as it says in the picture), but I am uncertain whether it is one with a deliberately wider base. You might want to check out what’s there on eBay – from the pictures you should get an impression of how wide the base is. But keep in mind the maximum width of the base of the adapter is limited by the diameter of the MFT mount, and the distance that the adapter base is recessed into the mount. So, if your lenses are very wide already from the mount onwards, you will probably have difficulties finding any adapter to use them. Some lenses start getting wide a few millimeters behind the mount, those will fit into an adapter more easily (e.g. the Schneider-Kreuznach 25mm f/0.95).
I’ve read that using a 2X extender on a c-mount lens enlarges the image circle and eliminates the vignetting, although that increases the cost of using a c-mount lens. Do you have any experience using 2X extenders?
No, I don’t. A 2x extender will magnify picture by 2x, like zooming in. Using an extender may also lessen the reolution, but probably not as much as a digital zoom function. I guess this is only useful with very short focal legths, as the 25mm I reviewed here would effectively become a 100mm tele lens on Micro Four Thirds. But if you want an f/1.4 tele, using an extender on a C mount lens might actually be a cost effective solution.
I’m afraid they don’t perform exactly the same in terms of speed. The second picture is a little brighter than the first one.
Thanks for pointing that out! One would expect the 25/1.4 to be half a stop faster. But the camera’s metering claims otherwise. But since I used integral metering, maybe this is to do with the lens’ vignetting wide open. Maybe this test should be redone using spot metering.
I was being bored and did a little experiment using Photoshop. I gave the first picture +0.3EV and it turned out almost exactly the same in terms of brightness with the second one. So I think the pentax can live up to its f1.4 aperture. ^_^
Cool, thanks! If you like, you can send me the pictures and I will include them in the article.