You know what we need?

[RichA]

A machining service to deal with these lenses. The shot below was taken with a Cosmicar (Pentax) 12.5mm f1.4 1" CCTV lens on a Panasonic G1. That is as far as I can get with that lens from an object right now. The Cosmicars are exceptionally good. Not inferior to the Schneiders and the Angenieux lenses in any way, and you can still buy them at affordable prices. But, the 12.5mm has a very slightly too wide back that won't fit into the recess of the 4/3rds to c-mount adapter. So, about 1mm needs to be taken off for it to fit. We're talking about 10 minutes for a machinist and a small lathe. A service like that, even one to make a new rear retaining cap to replace the original for these kinds of lenses would be good, and the costs would be low, maybe $40-$50 for basic jobs like that.

 

[kds315]

...but unfortunately you seem to forget that the poor machinist might not be willing to take the risk of mounting the lens to his lathe, since it might damage it...had that discussion already...

 

[Godfrey]

...but unfortunately you seem to forget that the poor machinist might not be willing to take the risk of mounting the lens to his lathe, since it might damage it...had that discussion already...

The brass base comes off the Cosmicar 12.5mm f/1.4 with three grub screws in a half a moment. Very easy to chuck in a lathe and turn. Only problem is that to fit it to the C-mount adapter, it needs to be relieved about a third of the way up the grub screw threads so you might need to run a tap through them to refit the base to the lens, but it's not hard at all to work with. There's plenty of meat for the grub screws to be re-fitted and hold the lens body securely.

I'm no machinist, but I did mine in about 10 minutes on a borrowed lathe.

 

[RichA]

...but unfortunately you seem to forget that the poor machinist might not be willing to take the risk of mounting the lens to his lathe, since it might damage it...had that discussion already...

Any machinist who would chuck the whole lens has a screw loose.

 

[Vivek]

You know what we need?

Just a small (cheap) key file and ~30mins of filing for each flange. It is important to note that even rough finishes will not affect the planarity of the flange (where it meets the adapter) since only the sides are trimmed and the cosmetics will not not show when the lens is mounted on an adapter.

Some of us do not need a machinist for jobs like this.

 

[wjlapier]

This service did exist at one time on this forum. I had a Comiscar 12.5/1.4 and Tevidon 25/1.4 modded back then.

But I agree with Vivek. I modded two of my c-mounts so I could obtain infinity focus. Wasn't the prettiest mod, but the results were fine.

 

[RichA]

This service did exist at one time on this forum. I had a Comiscar 12.5/1.4 and Tevidon 25/1.4 modded back then.

But I agree with Vivek. I modded two of my c-mounts so I could obtain infinity focus. Wasn't the prettiest mod, but the results were fine.

I'm still debating doing it with the Cosmicar 12.5mm. I've seen lathed mods and they actually show a clean ring of material removed, not a bevel, but an actual squared off reduction in rear barrel diameter sufficient to clear the adapter shoulder. I hope there is enough material to simply file a bevel.

 

[woodmancy]

I'm still debating doing it with the Cosmicar 12.5mm. I've seen lathed mods and they actually show a clean ring of material removed, not a bevel, but an actual squared off reduction in rear barrel diameter sufficient to clear the adapter shoulder. I hope there is enough material to simply file a bevel.

I wonder if someone who has tried the Vivek approach could post a picture of the result? I have a Cosmicar and I am very tempted to do this myself, with a file.

Keith

 

[Vivek]

This is a Fujinon-TV 25/1.4 (example- gives an idea):

An important lesson learnt from this:

The file slips while filing. So mask all the areas that aren't going to be filed.

I was able to inform Y.B. Hudson of this and he may have a cleaner looking end product.

 

[thearne3]

Here is another example. Pictured lenses are Computar 25mm and 12.5mm. I used a fine three sided file for about 30 minutes on each. Close to a clean notch. Careful not to go any farther toward center than necessary - I have an extra 12.5mm for parts because I filed off too much and the base broke off! Also, as Vivek noted: mask the areas not being filed - both for cosmetic reasons and to avoid fine filings in the moving parts of the lens. I use black electrical tape.

Best,
Tom

 

[slosync]

Filed Cosmicar

Here is a Cosmicar I filed at home. Note how far up the flange you have to go to have it fit into the adapter... I tried to keep the file at approximately a 45 degree angle while filing. If you note Tom's picture above you can see you don't have to go past the set screws if you have it machined.

Cheers,
Don

 

[woodmancy]

Thanks everyone for these pictures, I'm starting tomorrow!

Keith

 

[RichA]

Here is another example. Pictured lenses are Computar 25mm and 12.5mm. I used a fine three sided file for about 30 minutes on each. Close to a clean notch. Careful not to go any farther toward center than necessary - I have an extra 12.5mm for parts because I filed off too much and the base broke off! Also, as Vivek noted: mask the areas not being filed - both for cosmetic reasons and to avoid fine filings in the moving parts of the lens. I use black electrical tape.

Best,
Tom

If I could file like that, I'd be a human lathe!

 

[RichA]

BTW, the Fuji 25mm f1.4 in the picture was easy because it had a retaining ring that I could remove (not a base with integrated c-mount like the Cosmicars). I replaced it with the sliced off top of a black film container. I wish they were all that easy.

 

[ecsh]

If someone has a seriously screwed up lens they want me to try and get better, i use both a lathe and mill at home. PM me if your interested, as i would like to see what can be done to make this look better than some of the examples above, LOL.
Joe

 

[LizaWitz]

Wouldn't it be better to make the well of the C-mount adapter a bit wider, rather than to modify every lens?

 

[Vivek]

If someone has a seriously screwed up lens they want me to try and get better, i use both a lathe and mill at home. PM me if your interested, as i would like to see what can be done to make this look better than some of the examples above, LOL.
Joe

Sample from that Fujinon-TV 25/1.4 (f/1.4)

Try making something that.

BTW, the Fuji 25mm f1.4 in the picture was easy because it had a retaining ring that I could remove (not a base with integrated c-mount like the Cosmicars). I replaced it with the sliced off top of a black film container. I wish they were all that easy.

I found that out later. Anyway, the Fujinon is harder because it is a tough aluminium alloy as opposed to the soft Cosmicar/Computar brass flanges.

 

[thearne3]

Wouldn't it be better to make the well of the C-mount adapter a bit wider, rather than to modify every lens?

Liza,

I can only speak for the RJ Camera adapter - doesn't appear to have enough material. But perhaps you were referring to a change in the manufacturing spec? ...that would be the best option! I can see no reason why the Far East sources could no modify the adapter to accommodate the wider shoulder of many lenses. I wonder if we could develop a consensus spec and 'campaign' (email the various sources) for it? Hard to imagine this has not already been done...

Best,
Tom

 

[carsonc]

share my experience too

 

[Y.B.Hudson III]

how did I miss this thread?

fuji 25mm...