Thanks Bill. It's complicated for me to know: some C-mounts are regular 16mm, having slightly less coverage than the Super16mm lenses. Then the camera itself has several aspect ratio options on the sensor, so exactly what size will the 16:9 video aspect ratio be? Hopefully, it will use the maximum sensor width and be cropped top/bottom. But strange that someone has made a C-mount adapter if it's not really usable (I can't remember what page I saw it on now -- I've recently been darting from different forums all over again, like I did when the D90 first came out, trying to nail down what my personal rig might be made up from if I got a G1H).

Well, I browsed a few photography forums and it seems some still photographers have already been using C-mount lenses on the Lumix G1, so this is very encouraging for us. This is what I learned:

The C-mount flange-to-film/sensor distance is 17.526mm, and for MFT it is 20mm. So any C-mount lens will have to intrude about 2.5mm into a MFT camera. Because EVF cameras have no mirror box this isn't such a problem. However, beware some C-mount lenses have extended optical elements beyond the lens threads, and this is a distance too far for the workings of the camera. Simplistically, if nothing extends past the lens thread, you will probably be ok.

This is not to say a particular lens will have a big enough lens circle (some older cine lenses have a very small diameter rear element). But since video is shot in the camera's 16:9 aspect ratio this gives the best chance of escaping corner vignetting. If you are framing for 1.85 or CinemaScope, you'll have even more cropping potential to clear a vignette from an otherwise useful lens.

There are so many different C-mount lenses out there, made over a long period of time, so personal recommendations about what works for MFT will be useful for people buying lenses unseen over the net. My usual C-mount advice is to be prepared for extra collimation costs for older lenses, and this may be even less forgiving when used on a densely packed camera sensor.

Sorry, forgot to include the links -- these were the two best sites I came across today (new to me) which you might find interesting:

http://www.rangefinderforum.com/forums/ (see the MFT section -- couldn't get direct link to work).

http://forum.getdpi.com/forum/forumdisplay.php?f=44

Another consideration I found out about C-mount/MFT adapters is that the designs include a stepped inner ring (to recess the C-mount lens). If the bottom barrel diameter of a C-mount lens is larger than the adapter ring, this will stop you being able to screw the lens fully home. In acknowledgement of this importance, the adapters often quote the diameter of the step ring (in the one's I have seen so far online, it's anything between 36.9mm to 37.2mm). So C-mount lens choice for the GH1 will be partly governed by this mechanical restriction (though some enthusiasts have already had a bit shaved off their lenses to solve this!). You have to physically measure the bottom barrel diameter of a lens because it's not usually something which will be quoted (doesn't normally matter), so this is another hurdle to be mindful of when buying.

So, if you can find a C-mount lens, that hopefully doesn't need expensive servicing, with a small enough barrel diameter to fit the adapter ring, without an overly extended rear optical element to plough into the internal buffering, which has a wide enough circle to cover 16:9 on the GH1 sensor without vignetting -- phew! -- then you should be good to go.

Sounds like a lot of hoops to jump through, but I'm encouraged that some of these still photographers have been surprised with the "character" of these older cine lenses. I thought the new Fujinon machine vision lenses for megapixel cameras might be a good bet (reasonable price, very sharp, no hunting around in the second hand market), but I think their lens barrel diameter might be too much for the current adapters for the reasons noted above. Perhaps someone could measure some? I'll shut up now...

The information I quoted is most of what I know about C-mount.
And the C standing for 'Cine'.

I ended up getting a nice mini-history of movie film formats.

Historic sub-35 mm Film Formats & Cameras

16 mm film - Wikipedia, the free encyclopedia

I thought it might be worth redoing these calculations given we now know the GH1 is NOT wrapping 24p inside a 60i container.

Actually doing a rough calculation, Both doing 1920x1080:
Canon 5D2, 42 Mbps, 30 frames/sec., so about 1.40 Mb/frame
Panny GH1, 17 Mbps, 24 frames/sec., so about .708 Mb/frame.
Canon Vixia HF S10, 24 Mbps, 30 frames/sec., so about .800 Mb/frame
Panasonic HMC150, , 24 Mbps, 30 frames/sec., so about .800 Mb/frame

So for Panny to crank the GH1 bitrate up, that will be next years model.
I still think u4/3rds would be a hell of a platform to build a real video camera around.
But that's probably just my imagination running wild.
On the other hand, this will be the first time I know of that a camera manufacturer specially designed a pair of lenses just for video work.

MY sample was pure 24.0. By June, Pana could have added pulldown.

Unless they are watching the feedback.

Trying to be depressing, or does it come naturally? ;-(

I was looking at the Panasonic GY-HM100U & HMC150 and imagining them rebuilt around a u4/3rds lens+sensor core. It was nice while it lasted. Among the nice things about this format for Panasonic is that it will be very difficult for Canon, Nikon, or Samsung to easily match the zoom range and light weight of u4/3rds lenses as they are trying to build on an even larger sensor base (APS-C, FF 35mm).

Ok , I need a little help understanding how C Mount lenses can be used on m4/3 cameras . My understanding is that most C Mount lenses for 16mm don't even have an image circle large enough for s16 . So how could they , if 16mm camera aperture is about 10.3 x 7.5mm and m4/3 sensor size is 18 x 13.5mm , work without real bad vignetting , and maintain infinity focus ? thanks

No power zoom and now this:

[PMA] Panasonic SLR Camera Reflects Difficulty of AF Development

Panasonic Corp exhibited its lens-interchangeable camera "DMC-GH1," which will be released by the end of July 2009, at the Photo Marketing Association (PMA) show.

The camera can record HD video in 1080/24p or 720/60p AVCHD format. And it can output 1080/60i video on a TV when decoding (replaying) HD video, according to the company. The SoC hardware to improve image quality and the image sensor's pixel structure in the DMC-GH1 are the same as those seen in the DMC-G1.

The DMC-GH1 (prototype) has an auto focus (AF) video recording function that users might find strange. Specifically, the AF function does not work when the zoom ring is turned after the video button is pressed.

There are two methods of avoiding this problem.

(1) Focusing the camera on the subject by half-pressing the shutter button after rotating the zoom ring.

(2) Presetting the AF mode dial on the upper left hand side of the camera body to AFC mode (which continuously focuses on different subjects like a camcorder) before pressing the video button.

In other words, the first method uses AFS (auto focus-single) mode (in which the camera focuses on the subject only when the shutter button is pressed), which is useful for doing things like filming a movie. For example, to produce a movie effect, it is possible to focus on a man in the foreground while he is speaking and shift the focus to a woman in the background as she starts speaking.

On the other hand, this mode is not suited for following and shooting a running child using the zoom function, for example.

Though the second method is effective in such a case, still camera users usually shoot images in AFS mode. So, they have to remember to switch the AF mode dial to AFC before pressing the video button. As far as I could tell from the exhibited model, however, the camera's focus in AFC mode did not seem very accurate.

If the trouble of switching the dial causes a negative user experience, what must be done is very clear. It is to automatically switch the mode to AFC when the video button is pressed, even though the AF mode dial indicates AFS. And Panasonic should tell users that the AF mode dial can be used only for still images.

When I asked Panasonic at its booth if it is planning to add a function to automatically switch to AFC mode, the company gave me two different responses. One person denied it. But another neither confirmed nor denied it, just saying the camera is still under development.

I don't know which is the case. But supplementary explanation of the first person was interesting because it was about the difficulty of the development of the unprecedented auto focus function.

First, the DMC-GH1 is equipped with a 4/3-inch image sensor. And it has a much shallower depth of field than, for example, broadcast cameras with a 2/3-inch image sensor. Therefore, it is difficult for the camera to automatically continue to focus on the moving subject and shoot a movie that does not make viewers feel uncomfortable.

Moreover, Panasonic developed the AF capability of the DMC-GH1 based on the DMC-G1's AF function, which can be used only for taking still pictures. The DMC-G1's AF is very accurate in AFS mode, and it was realized through sudden focus shifts and slight camera shakes. So, this is possible only with still images.

It will take more time for Panasonic to eliminate the problems caused by such motions and achieve a high focus accuracy in AFC mode, said the person who denied the possibility that the company will enable the camera to automatically switch to AFC mode.

======

This is interesting because I kept trying to see what the switch did and when I asked the rep he avoided a direct answer when I said a lower quality AF mode was used when shooting video.

Kurth -- you are right, in theory C-mount lenses do not have practical image coverage for the MFT sensor. But it seems some C-mount lenses have a larger image circle than was necessary for 16mm or even S16mm. It is this unexpected extra which has made them usable for the MFT sensor. I'm as surprised as you; I thought I knew a little bit about C-mount cine lenses and this was a total unknown to me. However, I have to accept the fact that there are stills photographers using these lenses on the G1 right now. As expected, some lenses vignette on all the available aspect ratios and won't be any good, but amazingly a few do not vignette even on 4:3. Obviously, shooting in 16:9 gives video users the best option to escape the worst effects. However, since this extra coverage is coming from the edges of the lens which was never designed to be seen by a film frame, there may be softness as well as illumination fall off. At the moment, it's our friends the stills photographers who are making discoveries in this hit and miss affair, so we wait until more reports come in concerning the things we want to know about the performance of specific lenses (see my previous posts about what to look out for). Check out those photography links I posted and see for yourself what the photographers are saying about it and look at their sample images.

John - I followed a number of links to different sites and every example of a c mount lens on the g1 vignetted . Now these were all 4/3 and not 16/9 images but from my understanding the 16/9 image is wider on the sensor , so the problem would be worse . I'd love to be able to use c mount but I think that the scarlet will be the first camera to use them effectively obviously because the sensor is smaller . If Panasonic could issue a firmware mod that could , for c mount lenses , sample the video image from a smaller part of the sensor ( also increasing effective focal length ) then that would be cool. I'd love to be able to use my ole' 9.5-95mm ang.. Maybe the s16 canon lenses would work but they are very expensive .cheers/k

Kurth -- some examples I saw were clearly reported as having no vignette with 16:9, and this was confirmed by the image samples presented. I also saw many "white wall" tests showing the image circle fall-off. I spent many hours going through so many threads on several forums I did not keep a record, but the impression was certain lenses were usable, which certainly surprised me. At the moment only the G1 is available, so the filmmakers have to wait for the GH1 to carry out their own experiments to find out what's what. I have some C-mount primes which I will try on the GH1 if I get it.

yeh , I also have a 10mm ang that might be nice - I also have alot of canon fd mount lenses which might be more useful - someone somewhere should do a compatibility list when it's time . With this camera and with the scarlet , c mount lenses might become harder to find !

Kurth -- I made these quick notes when I was originally looking at the still photography websites. They are also hoping to get some sort of combined data about what's good and what's not. These contributions come from the getDPIWorkshop forum:

SOM-berthiot 25mm f0.95: “vivek” said covers all frame aspect ratios, but needs machining to fit adapter.

Pentax 25mm f1.4: “Monza” said covers 16:9.

Canon 50mm f1.8 TV lens: “wjlapier” said covers all frame aspect ratios.

SOM-Lyter 1” f1.9: “wjlapier” said covers all frame aspect ratios. Some edge smear.

Wollensak 1” f2.5: “wjlapier” said covers all frame aspect ratios. Some edge smear.

Bausch & Lomb 26m f1.9: “butterdada” said covers all frame aspect ratios. Soft when wide open.

My apologies if I got some of these conclusions wrong. Thanks to all these guys for putting down their money to find this stuff out for the rest of us.

There's a great c-mount lens compatability chart that's being maintained here:
G1 C Mount Lens Compatibility List - Google Docs

And here's a list of all the lens adapters available for the G1, and where to get them:
Panasonic Lumix G1 Lens Adapters