Is this an Arri S or B mount?

Matthew W. Phillips · January 9, 2013

I am looking for a lens adapter from CP to Arri so I can have a broader assortment of lenses. On eBay, a seller has what he thinks is an adapter from CP to Arri. The CP part is obvious to me since I have that mount on my Angie 12-120 (which I already hate.) The part I'm not familiar with is the Arri mount.

Can anyone tell me by the pics in this auction if this is an Arri S or Arri B mount? Or is it even one of those or is the seller mistaken?

Thanks.

http://www.ebay.com/itm/160937136141?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

Dom Jaeger · January 9, 2013

It's a somewhat dodgy B (for bayonet) mount. B mount lenses have the 2 tabs at the back of the mount. Usually they are fitted then twisted until a spring lever in the camera (or adapter) mount clicks into a cutout in the lens mount and locks them in. In this case, after fitting and twisting, a grub screw driven against the thin wall of the lens mount is the lock. A little dodgy, but it should work, the ID of 41mm is correct.

Steve Switaj · January 9, 2013

It's (mostly) a B mount.

You can tell because of the two milled slots for the mount "ears".

As Dom notes, this is a low-end mount. The better ones have a nicer locking mechanism and can stay the camera as a new mount. This one seemingly uses setscrews to retain the lens, and is meant to be attached to the lens and left there.

This is OK so long as the screws either have soft tips or some sort of pressure pad underneath them, otherwise, a normal set screw (made of hard alloy) will leave a ding in the (relatively) soft stainless steel of the lens mount, and you obviously don't want that.

Although this adapter clearly allows for B mounts, many set-screw type adapters could also take an S mount lens since the throat diameter and backfocus were the same. It's a matter of whether the setscrews are placed to get a good grip on the flange groove.

Rob Sanders · January 9, 2013

If I were you I wouldnt buy the one you showed us here on Ebay. Instead talk to Ken at Whitehouse Audio Visual here in California. He has the highest quality Arri B > Cp mount.

http://www.whitehouseaudiovisual.com/Mount_1.html

MOUNTc(lg).jpg

Gregg MacPherson · January 9, 2013

This one seemingly uses setscrews to retain the lens, and is meant to be attached to the lens and left there.

There are a few cheap lens mount adapters to fit Arri mount lenses that literally fasten the adapter to the side of the Arri mount with set screws. A better kind has the screws at an angle so they apply pressure to the B mount tabs. At least it's better at assuring the lens is seated on the flange. The adapter Matthew pointed to on eBay, an Arri B mount lens is twisted untill you have a friction lock with the tabs. If one was switching out primes all day on an indie shoot the mount would stay in the camera and the set screw lock would not be used.

Obviously it's not as nice a design as the locking one at Whitehouse, but if its machined correctly for back focus and it's stainless then it could be usefull. It's a cheap price. The locking type may come up cheap on eBay if one is patient.

Matthew W. Phillips · January 9, 2013

I understand the concerns about this adapter. But all I need to know it if it will work if I only need it for one lens. I was thinking about purchasing a Vario Sonnar 10-100 to use as my primary zoom instead of the stock Angie 12-120. Would this adapter be okay for putting on the Zeiss and leaving it there? It wont break off or anything most likely?