Navitar 6mm F1.4 C mount

Will such a short lens work on the GH1 without severe vignetting? I've seen pics of people using glass twice as long on m43 and the image is just a small circle in the middle of the frame. God, i would love if this lens and a C-mount adapter would work well. A really wide, fast lens is something I'd use the hell out of.
 
This lens is for a 1/2" chip security camera. It will vignette severely without a tele-extender on the back end. When you add the tele-extender it will no longer be a very fast lens. Around f3.5 with a 2.6x.
 
Razz16mm said:
This lens is for a 1/2" chip security camera. It will vignette severely without a tele-extender on the back end. When you add the tele-extender it will no longer be a very fast lens. Around f3.5 with a 2.6x.
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The 2.6X feature on the GH2 is via sensor crop so I doubt it affects the f-stop. And I've read it should allow use of lenses for 1/2" chips ... good luck!
 
If this experiment works, and the GH2 allows the use of 6mm CCTV glass, that's it, I'm getting one. I look forward to the results of this experiment.

GrahamH said:
The 2.6X feature on the GH2 is via sensor crop so I doubt it affects the f-stop. And I've read it should allow use of lenses for 1/2" chips ... good luck!
Click to expand...
 
I've thought about this carefully.

On a Full Frame 35mm format sensor (e.g. Canon 5D)
A 6mm F1.4 C-mount (1/2 inch format) will "look" like a 6mm F1.4 lens with severe pin hole vignetting on 35mm format.

On a m4/3 sensor (default 2x crop factor, e.g. GH1) but ALSO using the 2.6x Crop Mode (1:1 pixels)
A 6mm F1.4 C-mount (1/2 inch format) will "look" like a 31.2mm F7.3 lens (but with the low light abilities of an F1.4 lens) on 35mm format.

Reason:
FOV = (Crop Factor A x Focal Length) x Crop Factor B = (2 x 6) x 2.6 = 31.2

OR

m4/3 sensor = 21.6mm diagonal image circle
1/2 inch sensor = 12.7mm diagonal image circle
m4/3 sensor with additional 2.6x crop = 8.3mm diagonal image circle (21.6/2.6=8.3)
35mm full frame = 43.3mm diagonal image circle

43.3mm/8.3mm = 5.2x crop factor!

F1.4 Depth of Field x 5.2 crop factor = F 7.3


Resources
See page 10 of:
http://www.zeiss.com/C12567A8003B8B6F/EmbedTitelIntern/CLN_35_Bokeh_EN/$File/CLN35_Bokeh_en.pdf


Note: this assumes the 2.6x crop mode refers to extending the 2x sensor crop factor by an additional 2.6x not just 0.6x.
 
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The image diagonal with a 1/2" chip is 8mm, at least according to wikipedia. As the 2.6x crop gives the function of a sensor with an 8.3mm diagonal, the image's FOV on your GH2 would be very slightly wider than you would get from using the lens on a 1/2" camera. But yeah, the lens would basically function as the equivalent of a 31mm lens on a full-frame camera (or 15.5mm lens on a 4/3" camera).

Haven't seen any decent-looking 1/2" lens smaller than 6mm -- do they exist? It seems that 1/3" sensor c-mounts would be quite usable with the 720p 3.9x tele-conversion (1/3" diagonal is 5.5mm compared to the 3.9x crop's 6mm,) I wonder if that would open up any interesting avenues.
 
Got the lens, doesn't focus right, yet, but I bet I can sand it into shape. Circle looks about the right size to cut into with the 2.6x.

Playing with the lens in front of the sensor, it seems to come into focus both inside the body a bit and about three inches away from it -- I suppose this is just a normal phenomenon with lenses, but I've never noticed it before.

Doesn't look terribly high quality, but better than those little $30 25mm's and 35mm's from China, at least.
 
Oh, I suppose that's extension tube effect...

Not looking too good, I'm not sure I can get it close enough without really screwing with it. Maybe I can get it shimmed up just right with some tubes and do something with it.
 
pomoville said:
Oh, I suppose that's extension tube effect...

Not looking too good, I'm not sure I can get it close enough without really screwing with it. Maybe I can get it shimmed up just right with some tubes and do something with it.
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well? got the GH2? show some footage with the 6mm+crop :)
 
pomoville said:
Got the lens, doesn't focus right, yet, but I bet I can sand it into shape.
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The problem is with the c-mount adapters people are selling. They're selling c-mount adapters that work fine for cinema lenses (16mm c-mount) but not for security-camera lenses. Security camera lenses have wider diameter rear casings, and they just won't fit into the narrower-diameter cinema c-mount adapters. Somebody has to get Ciecio7 or one of the other makers to make a c-mount adapter that has a wider base for the lens to seat into.
 
Barry_Green said:
The problem is with the c-mount adapters people are selling. They're selling c-mount adapters that work fine for cinema lenses (16mm c-mount) but not for security-camera lenses. Security camera lenses have wider diameter rear casings, and they just won't fit into the narrower-diameter cinema c-mount adapters. Somebody has to get Ciecio7 or one of the other makers to make a c-mount adapter that has a wider base for the lens to seat into.
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how about 8mm c-mount ? can i get one that will work with 8mm bolex lens?
 
Bolex had a slightly different mount, especially on the wide angles, because the Bolex had a prism instead of a spinning mirror. Bolex lenses were called "RX" mount. They would mount on a regular c-mount, but wouldn't necessarily focus correctly (or something; I don't remember the exact difference, I was never much of a Bolex guy).
 
Barry_Green said:
Bolex had a slightly different mount, especially on the wide angles, because the Bolex had a prism instead of a spinning mirror. Bolex lenses were called "RX" mount. They would mount on a regular c-mount, but wouldn't necessarily focus correctly (or something; I don't remember the exact difference, I was never much of a Bolex guy).
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mmm.. interesting.. i may seriously consider getting a 6mm RX... so you're basically saying the c-mount is NOT a problem with those lens.
the only problem you can recall is not focusing right.. is it crucial? like not getting infinity? or just a "numbers" issue and can be focused fine by hand ?
 
Found it...
http://www.bolexcollector.com/articles/07_03_21.html

Basically they're saying if you put an RX lens on a regular camera, it'll work but the image will suck. The RX lenses are designed to provide different spherical aberration correction than regular lenses, because the RX lenses are designed to go through the prism that Bolex RX models had, whereas regular c-mount lenses aren't and don't. So if you put an RX lens on a regular (non-prism) camera, you'll get lousy contrast and soft images, especially when wide open.

The gist of the article is: only use a Bolex RX lens on a Bolex RX camera. Don't try to use a Bolex RX lens on any other kind of camera.
 
Anyone have some luck with a 6mm c-mount lens? Can you confirm Barry's description of the CCTV c-mount requiring a wider diameter flange to rest against? Can someone elaborate on this, as I'd like to think up a DIY solution.
 
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