C-mount adapter lens compatabilty

[TomBah]

I wanted to raise this question for everybody in the forum: I have recently purchased a GH1 and a Hawke Peng adapter: http://cgi.ebay.com/C5-type-TV-Bole...ItemQQptZLens_Accessories?hash=item4a9bd9af09. However, since my c-mount lenses have rear diameter of 40mm, they will not focus to infinity with this adapter (Linos lenses, based on Rodenstock optics).
I have contacted several e-bay sellers, but no one could answer me if there is in existence a c-mount to m4/3 adapter which allows these larger lenses to reach infinity focus. From basic scrutiny of camera, lenses and adapter, it seems possible to manufacture such an adapter. Does anybody have knowledge of this problem, and a possible solution (aside of machining the lenses, which is crude and impossible in my case). Any help will be most appreciated, for these and other lenses.

 

[Vivek]

I think you need to look for a c-mount to M39 adapter that will fit your c-adapter.

Replace the c-mount to M39 adapter present in your Rodenstock focus mount and use it with the adapter combination I mentioned above.

 

[MRfanny]

will a cmount to M39 onto an M39 to micro 4/3 work? does extending the distance because your stacking adapters affect image? excuse my ignorance.

 

[Vivek]

I just realised that the lenses TomBah referred to aren't what I had in mind.

Perhaps, those lenses need the removal of the c-mount flange and re mounting in a m4/3rds flange.

 

[laptoprob]

It's not about the 39mm screw adapter: it's the max. available size within the M4/3 bayonet. This maximum is 37,2mm in the adapter you already bought. I'd wait 'till you get the adapter and then see if you can shave a bit off of the lens 40mm rear. Maybe you can unscrew this part? I don't think there is another 1,5mm to spare in the regular adapters.

 

[MRfanny]

Perhaps, those lenses need the removal of the c-mount flange and re mounting in a m4/3rds flange.

Is this easy to do? I've taken the rear cmount flange off my lens and it fits perfectly but problem is the flange has the thread on it..ha it is also not thick and deep enough for me to shave 4mm off it so its a dead duck. I could just machine it down and superglue it back onto the lens but that's super last resort backyard mechanic style..lol pity cause the images look great.

 

[Vivek]

Don't know. Depends on the lens.

 

[laptoprob]

I just measured the m4/3 'throat', the inside of the bayonet mount. Something like 38mm. So anything bigger than the 37mm some adapters offer will never fit.
You will have to graft/glue the m4/3 mount onto the lens, no other way.
What is the rear diameter with the flange removed?

 

[MRfanny]

my adapter has a 37.2 mm opening. my rear flange measures 41.7mm. i took it off to see if the walls were thick enough for me to machine but they are not. i'd end up with a piece of foil as side walls if i did..ha.

Im considering just doing it anyways and gluing it back on because it has the cmount thread on it. the more expensive option is to just permanently screw it to another cmount adapter from the back..lol

or i could just buy that pentax one=)

 

[laptoprob]

Basically all you need is the m4/3 adapter at the correct 'depth', relative to the C-mount threads. That should justify the means I guess. And the lens will have to fit in the m4/3 bayonet, so you will have to permanently unscrew the C-mount flange to get infinity focus. Is the lens without the C-mount thin enough?

 

[MRfanny]

without the cmount flange it fits perfectly with a diameter of 36.8 and gets infinity focus if you adjust for the missing 1mm thickness of the base of the flange. Ive held it by hand onto the adapter and it works perfectly.

If i buy another adapter for it, i may as well pick up a pentax like you did with no fitting dramas..lol

here's a clip i did of the lens and using it at the end so you can get an idea of what it looks like.

http://www.vimeo.com/7638600