Based on my last few posts, it would seem like all I shoot with are C-mount lenses. I swear I shoot with other lenses too! I just thought I'd get these out of the way since I'll be going overseas not too long from now and it should be all Micro Four Thirds when that happens. I may even be jumping into a new system but I don't want to jinx it so I'll keep my lips sealed for now.
My main reason for doing this 2-in-1 review is that I feel the same way towards both of these lenses. I'll get this out of the way now... Neither the Cosmicar 6mm f1.2 or the 25mm f1.8 are spectacular so if that's what you're after, you can pretty much skip this review. They aren't on the top of my list of favourite lenses to use although not because I think they're horrible. They're okay, I just have better options in my arsenal. But if any of these lenses happen to fall into your lap or you're able to get a good price on them then it might be worth experimenting with. And to be fair, you can do far worse when delving into the world of C-mount lenses.
Cosmicar 6mm f1.2
A couple of things before I get started...
#1: This lens won't achieve infinity focus when screwed into a C-mount to Micro Four Thirds adapter without modification. And by that I mean filing down the edges of the rear lens mount.
#2: This lens heavily vignettes when used on M4/3. Most of the newer M4/3 cameras have a digital teleconverter function but even when I enabled this on my Olympus Pen E-P3 (2x maginfication of the image) there's still some vignetting. You'll have to shoot it at 16:9 aspect ratio to minimise the vignette. Vignetting is a non issue on the Pentax Q.
|Uncropped image, shot using an Olympus Pen E-P3|
|Shot using an Olympus E-P3 with the 2x Digital Teleconverter function enabled|
With the 2x Digital Teleconverter function enabled on my Olympus Pen E-P3, this becomes a 12mm lens for M4/3 (24mm full frame equivalent). On the Pentax Q, the full frame equivalent focal length is approximately 33.6mm.
Images are soft when shot wide open at f1.2. If you're shooting with M4/3, it can be usable under certain conditions. It's way too soft though when used on a Pentax Q to the point where I'm scared to open it that wide at any time. At f2, it's pretty good on M4/3 although still fairly soft on the Q. It sharpens up nicely at f2.8 and it's at its sharpest between f4 and f5.6.
There's corner softness at most apertures although things improve when you stop down. Plenty of chromatic aberration in the corners and also when shooting a high contrast scene. You'll notice some distortion when shooting straight lines.
This doesn't seem to be the most practical lens to get for the Pentax Q since anything wider than f2.8 is soft. The 02 Standard Zoom 5-15mm lens is f2.8 at it's widest so if you have that lens already, you'll probably be much happier with that. But if you don't have that lens and you're able to find this lens fairly cheap then you might be able to have some fun with it.
As for its use on M4/3 cameras, don't get it unless you're okay to shoot using the digital teleconverter function or if you don't mind cropping later on. There are other lenses that are close to the 12mm focal length (both native and adapted lenses) but if you have to have a small lens with an f1.2 aperture then this might do in a pinch. I can say that I've enjoyed using this more on my Olympus Pen E-P3 than on my Pentax Q, maybe because I don't have to worry about the ridiculous softness at the wider apertures.
While I don't record a lot of videos, I think this lens should do pretty well when shooting videos. People don't tend to scrutinize videos as much as they do still images. There may be times when low light performance is more important and you may be able to forgive the shortcomings. The vignetting even disappears when shooting video on an Olympus camera since they tend to slightly crop the image during video recording so no need to worry about that.
Cosmicar 25mm f1.8
The 25mm I have does not say 'Cosmicar' anywhere on it but if you do some digging around, you'll discover that it looks exactly the same as a Cosmicar 25mm f1.8. So I don't know, maybe they just didn't put the branding on the copy I got.
I'm not going to lie, there are better options in this focal length if you're planning on using this with a M4/3 camera. Among the C-mount lenses, I've personally owned the Computar 25mm f1.3 and the Pentax Cosmicar 25mm f1.4. I can say that this lens produces less barrel distortion that those two but I much prefer the images rended by those other two lenses. You also have the native lenses from Panasonic (the Leica branded 25mm f1.4) and the new one from Olympus (25mm f1.8), both of which are excellent. That said, you're probably looking to pay 10-15 times the amount (maybe more) for those native m4/3 lenses when compared to this lens.
Side note: I did have to modify this lens in the same way that I modified the Cosmicar 6mm f1.2, by filing down the edges of the rear lens mount. I didn't have to do that with the other lenses I just mentioned. So you'll need to ask yourself if it's worth the trouble. Unless of course you can find one that has already been modified.
No modifications needed on the Pentax Q. This lens has a full frame equivalent focal length of 140mm on the Q. If you like shooting with this focal length then this is a pretty handy lens to have. The reach is impressive given the size of the lens and I have no issues at all with how it handles on the Q.
No vignetting issues on the Pentax Q. There's vignetting when used on M4/3 but nothing that can't be overcome with some vignetting correction in post or by cropping a little. Or both. I've left the image below uncropped so you can see the extent of the vignetting. If you're shooting a bright scene then it will be very noticeable.
Depending on the scene you're shooting, a little vignetting may not be too bad. I actually tend to add some vignetting to my images in post so I don't mind this. But the vignetting can be corrected depending on the software you're using. See below for how your images can look when corrected for vignetting. We're essentially making the corners a bit brighter to match the rest of the image.
|Original image with no correction applied|
|Vignetting correction applied using Adobe Lightroom|
On both M4/3 and Pentax Q, centre sharpness is pretty good at f1.8. I have no reservations about shooting it wide open and it only gets better when stopped down. Sharpness is close to optimal at f2.8 and at its best around f4 and f5.6. I can't tel if it's sharper at f4 or f5.6, they look the same to me without doing any super pixel peeping.
When shooting with M4/3, you'll start to notice some softness about a quarter of the way from the edge of the frame so probably not a good idea to use this for landscapes or any scenes whereyou'd want the whole frame sharp. Should be okay though if you're mainly keeping your subject in the centre of the frame. All this isn't as much of an issue when shooting with the Pentax Q. There's softness but mostly confined to the extreme edges.
Chromatic aberration is controlled well enough, it's mostly confined to the extreme corners and even then, it isn't too noticeable unless you go looking for it and/or you're shooting a really high contrast scene.
I did not pay much for these lenses. The Cosmicar 6mm was almost free and the 25mm was bought for around $25. So while these lenses aren't my faves, they're pretty good value if you can get them at similar prices.
If you're shooting with M4/3, get the 6mm f1.2 if you need the focal length or the fast aperture. You may not use it all the time but it can be useful to own. Skip the 25mm f1.8 unless you can't get a hold of the other options although not a bad lens to have if that's all you've got.
If you have a Pentax Q then it's the opposite. Get the 6mm f1.2 only if you don't have any lenses at this focal length but the 25mm f1.8 can be a useful lens to have. I really like the reach that it has on the Q.
SAMPLE PHOTOS: Cosmicar 6mm f1.2
SAMPLE PHOTOS: Cosmicar 25mm f1.8
More photos taken using this lens are available on my Flickr page.