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Are These Arri-S or Arri-B Mounts? I'm Confused!


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I'm new to looking at vintage lenses, and I'm super excited to be picking up my first set soon - but these mounts have got me stumped. I've looked up Google as much as I can, and there's just not a whole lot I can find visually on the difference between Arr-S and Arri-B mounts - I intend to get a converter to PL mount so I can mount on my KOMODO, but I want to make sure I'm getting the right converter.

From what I know, Arri-S camera mounts have a thing sticking out one side that will hold the lens in place; Arri-B mounts have a two sided twist and lock mechanism.

These above are two different listings I'm looking at, but I'm just not sure is this Arri-S or Arri-B I'm looking at (especially with that funny screw thing for the lens on the left).

Some help please?

Edited by Joel Hanson Li
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The second one could be Arri S mount, hard to tell without seeing more of it. 

Generally eBay listings will correctly identify common mounts like this, so just searching for Arri S or Arri B lenses should give you a few examples to look at, although right now there aren’t very many B mounts on there.

The defining features of S or Standard mount are a straight cylindrical rear with a groove near the end when viewed from the side, and a slot (or sometimes two opposite each other) near the outer edge when viewed from the back. Different lenses might have different optical protrusions coming out of the cylinder. Here’s a few eBay Standard mount examples:

https://www.ebay.com/itm/284894575177
https://www.ebay.com/itm/334253654718
https://www.ebay.com/itm/373458008681

Note that the last example is actually a 16mm format lens, but the seller doesn’t mention it. 
You also need to watch out for older Arri S mount lenses, which require different adapter types that allow the cylinder part of the mount to rotate - Cookes, some Schneiders, a few others. There are also a few other more obscure mounts that can look similar, so it can be a bit confusing.

Arri B or Bayonet mount lenses have a rear cylinder with two protruding lugs opposite each other when viewed from the side. They are pretty easy to identify as no other mounts look similar. Here’s a few eBay examples:

https://www.ebay.com/itm/284913653386
https://www.ebay.com/itm/275224575570

https://www.ebay.com/itm/372228787417

Again some of these are 16mm format lenses. As with S mounts, you can’t tell the format coverage just from the mount, although often 16mm lenses will have optics that protrude further back than 35mm ones. 

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Wow thank you for the very detailed explanation! I suspected the second one to be Arri S as well but I was thrown off by the presence of 2 grooves when I though I should just be seeing one groove - also, the listing itself said Arri S in the description, but Arri Bayonet in the item specifications.

Anyhow, here are more pictures of both.

 

Lens On Left

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Lens On Right

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Lens On Left

s-l500.jpg

 

I think the golden screw like mount was for screwing into this supposed mount - it says it's "Arriflex Standard Mount" which I assumed was the Arr-S mount. It also additionally said it used to sit on an Arriflex 16, if that helps?

 

Lens On Right

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This is the only side profile I'm seeing.

 

Both of these are Cooke Speed Panchro Series IIs.

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Yes Arriflex Standard mount is Arri S.

So the first one might be Arri S but the inner helical should be further inside and the outer mount shouldn’t completely unscrew like that. Might be missing something or incorrectly assembled. 

Second is definitely Arri S. It is the older type that needs to rotate inside the mount, so you need a Les Bosher style adapter, or the RafCamera one.

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Yes, I found the first one a little weird with the protrusions, and though it seems like the Rafcamera Arri S - PL adapter might still fit, I think the second one one might be a safer bet to get just because it looks alot more familiar to me.

Les Bosher's mount looks solid, but last I checked it's almost 3 - 4 times the price of Rafcamera's adapter!

My plan is to fit the Speed Panchro Series II with an Arri S - PL adapter, then fit it on a PL to RF adapter (DZOFilm's one) before mounting on the RED KOMODO (Super35) - there shouldn't be any problems about cropping or such right?

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I’m not familiar with Komodo or RF adapters but in theory it shouldn’t vignette.

The back focus might be a bit out with multiple adapters, but as long as you focus by eye and the lens reaches infinity it doesn’t matter so much with a prime.

A lot of Arri S adapters don’t quite fit certain cameras because they hit baffles inside the mount, I think RafCamera has a list if which cameras work with his Arri S adapter. It should  be ok coupled with an RF to PL adapter, but you’ll need to test it.

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I could be wrong, but it looks like that brass helical part was put on over the Arri-S mount. You may be able to remove that helical and get to the original mount. If you compare the lens to a known copy, you should be able to tell.

If the lens+adapter needs to be shimmed, you will miss the intended focus range. You might not be able to reach infinity focus, or you might have the opposite issue, where you are able to focus beyond infinity. If the latter, and if there was originally a hard stop for infinity, you won't be able to rely on the hard stop, plus you may not reach as close of focus as possible.

However, the lens+adapter might be close enough that it won't be that big of an issue.

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I know it looks unusual - the lens itself sits snugly in the brass helical, and which seems to be screwed into the supposed Arri S mount - it doesn't look like the lens head fits in the lens mount, and it definitely does not look like the usual known Arriflex mount Cooke Speed Panchros listed - and if turns out to not fit and just be a lens head I bought, I'd have to spend another 4K USD and a 1 year wait to get it rehoused before using. Dilemma!

Wow this whole shimming business sounds like quite a science by itself - here's hoping my lens+adapter idea (albeit it being 2 adapters) work!

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