Cosmicar 8mm

ahuyevshi

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I'm guessing either I got a crappy adapter, or this lens focus mechanism is broken... It is sharp as hell, minimum focusing is seriously less than 1/4 in.... For 30 bucks I think it might be a fun lens to keep in the bag....

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Alan Wolf

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distance focus?

How does it do with focus on far objects? My guess is that the reason it focusses so close is that the mount is further from the sensor than typical, so it's like you have a short extension tube built in. But it images great—nothing wrong with a really wide macro lens—it's very tempting actually!
 

OzRay

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Ray, not Oz
I thought that the likes of the Cosmicar 8mm was designed for 35mm film and so you should get full coverage of the sensor, but with less FOV than on 35mm film.

Cheers

Ray
 

Krang

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Feb 19, 2010
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How does it do with focus on far objects? My guess is that the reason it focusses so close is that the mount is further from the sensor than typical, so it's like you have a short extension tube built in. But it images great—nothing wrong with a really wide macro lens—it's very tempting actually!
Is this true? Have you tested on far away objects? And how much does it cover in video?
 

kai.e.g.

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My cosmicar 12.5mm was exactly the same. You need to machine the back end of it to allow it to fully screw into the m43rds adapter. Look up "cosmicar machining" (or modification, perhaps) in Google, and you should find some threads over at GetDPI describing the process.

@OZRay: These c-mount lenses weren't made for 35mm film. At best, they're designed for 16mm or Super 16mm film, though TV lenses like the cosmicars, computars, etc can also be intended for even smaller image sensors. You won't get full sensor coverage with any c-mount lens until at least 25mm (and even then it's pot-luck). 50mm and above will pretty much all safely cover the 4/3rds frame.
 

kai.e.g.

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I don't have access to a metal lathe - that would be the fastest way. The way I handled mine was to use the "reaming" tool of a Swiss Army Knife. It probably has another name; it's that short pointed tool with a thick cutting edge. I stacked a couple of books on the kitchen counter, put the knife on that and angled the tool just right, so that spinning the lens round & round upon a soft cloth very slowly ground away the metal that needed removing. You're basically doing exactly what a lathe does, only by hand. It took a couple of hours (? I took a lot of long breaks in between, so I'm not sure just how many hours). I also used a good metal file at times (once I'd established a good notch) - just resting the file in the notch and spinning the lens round & round.. I'll post a photograph of the back of my lens if that would be useful to you.

There's another option, too. The chap I purchased my Computar 25mm lens from had adjusted the focusing of the lens in such a way that it focused to infinity, without having to be screwed all the way into the adapter. This simply involves removing the screws in the lens barrel, which makes the focus ring free-spin, with no lock at either end. I did a very similar thing to my Elgeet 12mm (which required no machining, but its focus was way off). You should probably get better advice than mine from someone, though: I'm very new to this, but am happy that it all worked, maybe just out of pure luck :)
 

hohoho

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What kai.e.g. says.

The alternative is of course to pay somebody to do the work for you. If you have more cash than patience and you can't think of a closer alternative, there's Japan Exposures.
 

thearne3

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Jan 28, 2010
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I have the Computar 8.5mm f1.3. No machining required - a very small lens. I haven't taken any pictures with it recently, but will post.

I DO have a lot of experience with filing lenses - the 12.5mm and 25mm Computars require it. I use a fine three-sided file. Takes about 30mins. PM me for detailed info.

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ahuyevshi

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DJ adapters are cheap.. I got mine for 25 bucks... Unfortunately as I have been reading you really need to grind down the lens so it fits...
 

thearne3

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DJ -

Look on eBay 'c-mount adapter'. Here is a picture:

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kai.e.g.

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The Computar f1.3/25mm is wonderful on m4/3rds cameras. I just love it. It's annoying, because I'd really like to buy one of those terrific Lumix f1.7/20mm, but with the Computar, it's that much harder to justify the expense :-(
 

thearne3

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Ok. The snow slowed down enough to get out for some shots with the Computar 8.5mm. What I'm seeing is significant CA (blue) near the edges of the FOV. I've left it in for the first shot, so you can see what I mean. The second I tried to remove it - not completely successful with Aperture 3.0.

Here are three shots - all at around f5.6-8. Aperture has no effect on vignetting.

I look forward to seeing some shots from the Cosmicar 8.5mm!

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Here's one cropped square:
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