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PL Hard Mount for Zeiss 8-hole Lenses


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#1 Gregg MacPherson

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Posted 21 May 2012 - 07:26 AM

I was looking around to find an inexpensive way to re-mount some S16 Zeiss MKII primes from Arri-B to PL. They have the 8 screw hole pattern. Visual Products have some nice looking stainless ones, not inexpensive. I saw some inexpensive plated brass ones but I think they are were for Optar lenses. They came with a spacer ring that may help set the flange position.

Does anyone know the distance from the front of the PL mount (the drilled face that sits on the rear of the lens body) and the rear of the flange/wings?

Were the original Zeiss Arri-B mounts machined super accurately? What tolerance could one assume for that? If the PL remounts are really acurate will they still need re-shimming?

Cheers,
Gregg
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#2 Dom Jaeger

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Posted 21 May 2012 - 08:12 PM

Hi Gregg,

proper Zeiss mounts tend to be machined to pretty small tolerances, most PL mounts I've measured are one or two hundredths of a mm under 5.50mm from base to flange seat.

Swapping between Bayonet and PL is pretty straight forward, but I almost always need to adjust the shimming a little, usually no more than 0.05 mm.

Cheap PL mounts, on the other hand, can be way off sometimes. I've come across some where the flange wing thickness was so over-tolerance that the locking ring in the camera mount wouldn't go over them. They also often fail to have an undercut in the corner where flange meets rear, causing the lens to sit forward in certain camera mounts that don't have a sufficient chamfer.
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#3 Tom Jensen

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Posted 21 May 2012 - 08:28 PM

There are also adapters that go over the bayonet mount and tighten with screws.
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#4 Dom Jaeger

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Posted 21 May 2012 - 10:31 PM

There are also adapters that go over the bayonet mount and tighten with screws.


Personally I'd avoid the ones that use grub screws to attach, they tend to be cheap and nasty, come loose over time and can damage the bayonet mount. Far better are the type that secure with a lock ring, such as Visual Products sell:

http://visualproduct...2&Cat=8&Cat2=23

Unfortunately they're not cheap either. Adapters also should be checked for collimation, as even the well-made ones rarely slip on without needing a slight adjustment to the back-focus. What I've sometimes done for people on a budget is have them buy one good PL adapter, then I fit it to each of their Bayonet lenses and check and adjust the back-focus of each accordingly. Then they can swap the one adapter between all of their lenses. But they need to use a good adapter, and if they use the lenses in Bayonet mount again they need to replace the original shimming.

Feel free to ignore what I say though - in my job I have to be picky (and I've lost count of the number of times I've had to 'fix' someone's dodgy adapter from ebay), but plenty of people get by with the cheap stuff.
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#5 Tom Jensen

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Posted 22 May 2012 - 12:37 AM

No, it's true, though. When I was at Otto's back in the 80's we had a set with the screws and that's what made me think of it. The screws did come loose all the time and we had the luxury of a collimator and a projector as well as several lens techs. Fortunately, I was lucky enough to never have to use them.

Edited by Tom Jensen, 22 May 2012 - 12:39 AM.

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#6 Gregg MacPherson

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Posted 22 May 2012 - 05:10 AM

Hey thanks Dom, Tom.

If I can get some inexpensive hard mounts I would far prefer it. There are some fairly inexpensive interesting looking adapters that have better variations of the grub screw idea. I might round up the references and see what you think. But for now I'll research the hard mount idea and see what happens.

The plated brass hard mount I mentioned before is also an adaptor. I may get one on apro (meaning I can return it) to have a look. The vendor on eBay wasn't that helpful with measurements. From the photo it looks to me that the critical dimension from the mount base to the flange seat/rear of wings will be less than 5.5mm even with the spacer.
Here is the eBay URL
http://global.ebay.c...0710926766/item

I have a friend with a large CNC wjho may make the adapters for me for free. If the increment under 5.5mm is not that important I think he can make a consistent dimension for that from mount to mount (maybe within just a few microns). Before Dom's post I thought we had to be within a couple of microns of the idealized dimension. It's a ;lot easier if we don't. Wether he will be happy to make them in stainless I am less sure of. He would be happy using 6061-T6 aluminum or probably brass.

How long does it normally take to collimate a set of five S16 MK II primes? Steven Spooner at Panavision Auckland was friendly and keen to help. But he may have to do it after hours.

Dom I found the previous thread on Fabricating a PL mount which made me wonder about different versions of the mounts. Are you sure that the dimension given above as "one or two hundredths of a mm under 5.50mm from base to flange seat" is good for my S16 MKII lenses?

Cheers,
Gregg
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#7 Dom Jaeger

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Posted 22 May 2012 - 09:28 AM

As long as it's under 5.50 mm you can shim it up to within half a hundredth. They're purposely under tolerance for that reason. If it's over you're in trouble.

I take about an hour to collimate a set of primes, but it depends on how many need adjusting. I like to check them both at infinity on a bench collimator and at closer focus with a projector, in case there's a discrepancy with the scaling. Projecting also tells you if there are any issues with the lens - introduced aberrations, image shift, focus play etc.

If you've got a friend with a CNC machine then making your own mounts is a good option. If you can get hold of a proper Zeiss PL mount to give them they should be able to replicate it fairly easily. You could even make a few more than you need, sell them on ebay and make your outlay back.

The critical dimensions are the flange wing thickness and the rear diameter, and a consistent flatness of at least within a hundredth. And make sure they're undercut like the Zeiss ones. And all burrs should be removed.

I've had to deal with mounts that look exactly like the ebay ones you linked to that were full of burrs, not properly undercut, and sometimes over tolerance. But those were made in India for $40 each, whereas these are from a US supplier, right?... Should be fine then. B)
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#8 Gregg MacPherson

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Posted 22 May 2012 - 06:19 PM

I've had to deal with mounts that look exactly like the ebay ones you linked to that were full of burrs, not properly undercut, and sometimes over tolerance. But those were made in India for $40 each, whereas these are from a US supplier, right?... Should be fine then. B)


Yes very funny. I asked the vendor who the manufacturer was and he said he did not know. He said he has a lot of them. He didn't want to measure the thickness of the flange with base and the spacer ring. I'm wondering if he has a source of these in India or China.

I'm curious about the Indian made one you are refering to. Do you have any clues how to find that.

Cheers,
Gregg.
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#9 Dom Jaeger

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Posted 22 May 2012 - 09:21 PM

Yes very funny. I asked the vendor who the manufacturer was and he said he did not know. He said he has a lot of them. He didn't want to measure the thickness of the flange with base and the spacer ring.


The fact that he can't even be bothered measuring one for you should set alarm bells ringing.

I'm curious about the Indian made one you are refering to. Do you have any clues how to find that.


No, sorry. A client sourced them himself, my only involvement was the hours of de-burring, re-machining and adjusting that were required to actually make them useable.
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#10 Gregg MacPherson

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Posted 23 May 2012 - 08:12 PM

The fact that he can't even be bothered measuring one for you should set alarm bells ringing.

No, sorry. A client sourced them himself, my only involvement was the hours of de-burring, re-machining and adjusting that were required to actually make them useable.


Yes I was on full alert with that one, but I was still quite curious. If the price was $40 I would probably get one and have a look. Things like deburing and some re-machining where I wasn't messing with the resulting flange position I would just do at home.

Cheers, Gregg.
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