Questions about my camera, focusing and stabilization

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Robdoc

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Questions about my camera, focusing and stabilization

PostSat Jun 25, 2022 1:47 am

Hi everyone, 

I have a few questions and really hope that someone can help me out.

1. I have a BMPCC6K with a half cage. For some reason whenever I hook up a focus motor on it, the camera will jostle up and down when I use the focus.  I even got the Tulta nucleus nano wireless one and the same thing happens. This really worries me because I have a wedding to shoot for a friend in 2 weeks. Does anyone else experience this?

2. I just heard today that Blackmagic announced that they will have a in-body stabilization feature with a firmware update.. is that now, and would you take a chance doing a wedding handheld and do the stabilization after?

3. Can someone tell me what focus things they use on their handheld rigs? And, does it make the camera jostle up and down when you use it?
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rick.lang

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Questions about my camera, focusing and stabilization

PostSat Jun 25, 2022 3:52 am

General release of camera firmware 7.9 and the DaVinci Resolve 18.5 beta will work together. Can’t hurt to do the camera update and give it a go one the fifth beta of release 18. You would seem to have enough time to test right away and make a decision about using that approach for the the wedding. No pressure, eh? Bonne chance.

I use PD Movie currently for my focus control via a thumb controller on my rails. But I’m on a tripod when using it.
Rick Lang
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Jim Simon

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Re: Questions about my camera, focusing and stabilization

PostSat Jun 25, 2022 4:48 am

2. I've been doing handheld without stabilization for years. (Well, without post-stabilization. OIS lenses all the way, baby!)
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robert Hart

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Re: Questions about my camera, focusing and stabilization

PostSat Jun 25, 2022 11:09 am

Depending upon what lenses you are using with a small-bodied camera with stills-camera lens mounts, you have just about everything conspiring against you when adding a powered follow-focus.

Follow-focus motors tend to be powerful brutes. They have to be.

Simple spur gears attempt to force themselves apart. Ideally they and their shafts/bearings should be in a common rigid housing. That is one rule the typical swing-arm follow-focus breaks with several possible joints in the common structure, the camera to baseplate fixture, the lens to camera fixture, the support rods to camera fixture, the internal mechanism of the lens itself, the integrity of the swingarm of the follow focus throw, flex of the rods, the camera body itself and the lens body, it is something of a minor miracle a geared follow-focus works at all

Simple spur gears are mostly wider in diameter than the shafts they drive. Loading by the friction of shaft bearings against the gears driving them around is relatively low or they just would not be efficient. Most lenses break that rule in that the diameter of the bearing surface of their driven gear (the focus ring itself) is almost as wide as the driven gear. So pressure increases a friction load. The gears under load tend to add a separating force which in turn adds to the friction, a perfect storm and sometimes a cascade to failure when the gears force themselves apart and hop teeth.

So let's look at those points of fixture.

A full cage attached top and bottom to the camera body will help. A half cage may depend too much upon the firmness of the camera base to baseplate attachment. If there is no rubber, the camera will try to twist off its mounting screw unless the screw is very firmly tightened which may distort the camera body itself. If there is rubber on the base faces, then the joint may flex.

Rods into cage/baseplate. - How tight is the fit in the holes and how firmly are they are clamped in place? Some arrangements are better than others but most hollow rods will flex in the holes and along their length.

The attachment of the follow focus assembly onto rods. - By necessity, the contact area of the attachment must be narrow compared to the rods into the baseplate. If the fit to the rods is loose and requires a lot of tightening, then flex will inevitably occur there. Some follow focus motors attach to a single rod and their swing to engage the driven gear on the lens happens on the rod itself a wear point where clearance can open up.

The "offer-twist to lock" lens mount. - Nikon F-Mount, Canon EF-Mount, M43-Mount? These commonly maintain flange face firm contact by the use of a thin spring within the mount ring that the bayonet lugs of the lens tail engage against. Some non-genuine mounts do not use the springs but have built-in compliant faces the lugs engage against which function identically. These are often crudely achieved by slot cuts in the base material of the mount ring.

Why do it this way? Most bayonet-style stills-camera lens mounts also use a locking pin to stop the lens from twisting in the mount and falling out during focus movements. The lens must therefore rotate in the mount a fixed distance to allow the pin to engage. The spring arrangement allows for minute variations in machining of the lens tails, the inevitability of wear on the bayonet surfaces and to a much lesser extent the flange faces.

The rejection forces from a follow focus gear set tend to bend the lens body off-axis, especially if the lens focus system is damped with a high friction lube for smoothness and to maintain working tolerances by filling in the gaps. A point of yield will be the circular spring inside the lens mount which will cause the image to move as one side of the flange face opens up.

The PL-Mount eliminates this problem at expense of not having a locking pin on the twist ring but relies entirely on the fixed pin engagement with a matching slot in the lens tail, which is why you do not transport cameras with lenses mounted if you have any common sense. The Canon FP-Mount was a similar arrangement as are the B4-Mount and B3-Mount. The EF-Mount was really an evolutionary step backwards possibly driven by manufacturing cost.

There have been emulations of this system with alternative Canon EF-Mounts and Nikon F-Mounts offered. P+S Technik with its IMS system and I think RED Corp have had a go at positive lock mounts for Canon and Nikon bayonet style lens tails.

Some modern self-powered stills-camera lenses with plastic bodies eliminate damping frictions due the necessity to get the most out of the limited power available from internal servomotors. Simply allowing more generous clearances and an optional disconnect of the focus ring from the focus system when autofocus is selected introduces the possibility of image shifts when focus trims are made. Wear and age will weary them and make the issue worse for motion video work.

There is not much to be done about a sloppy lens except to buy something else.

The traditional externally mounted geared follow-focus is really just a workaround which became an industry standard and was eventually powered. ENG servo lenses were a far more elegant solution, some better than others.

So after all that barely scientific fluff and crappenstance discourse, what to do?

A full cage with upper and lower fixture for the camera will be helpful. A decent baseplate with snug fit around rods and cam levers versus split clamping is desirable.

Solid rather than hollow metal rods will be helpful to avoid torque bending of the rods.

A good solid bridgeplate and chair under the front of the lens plus a secure strap or even a saddle clamp across the front will be very helpful to resist torque bending. It will be absolutely useless if the lens body does not have internal focusing. Even a ziptie across to the rod most opposite the driving gear will be helpful but all this will make lens changes a pain in the ring.

Mike Patey of Best Tugs in the US has developed and vends reusable zip ties apparently to aviation standards. https://www.besttugs.com/

A good solid bridgeplate will be assisted by a mattebox with its own good solid bridge to further firm up the rods against bending.

So what about the corrugated spring inside the Canon EF-Mount and Nikon F-Mount? There is not much to be done as the fit is precise. You might be able to increase spring tension slightly by adding small shims under the spring but making those will be extremely complicated and frankly not worth the effort. - I have tried.

Compliance within the camera body itself from forces occurring between the lens mount and camera base. A full cage will spread the perimeter loading on the camera body but will not address concentrated loads occurring at the lens mount. Given the non-modular nature of the electronics layout, any compliance within the camera body is not ideal as it will work electrical joints which are a known weakness in modern leadless surface-mounted PCB designs.

The more you can stabilise the mechanical bond between the lens body and the rods/baseplate the better.

Now we run into the final dilemma. How long is a piece of string. You may build a tank of a setup, then do hour back in with the struggle and grunt of carting it about and get it caught in hedges or snag long flowing hair. (Note my political correctness in avoiding sexism). When the person grabs a hank of that long flowing hair to haul it free, you are fated to be pulled off your shot.

My first step would be to make a bridgeplate, chair and saddle for the front of the lens and incrementally build from there. The bridgeplate should be easy to get hold of but don't stuff around with those halfcircle clamp-ons or the cheap split circle and draw rods versions. For torsional strength both types are ornamental but poor in firmness.

The chair and saddle may have to be 3D printed or custom machined for the front of your lens.

Meanwhile, you can try a strong zip tie around the front of the lens body down to the rod most opposite the drive-gear-driven gear contact point and cut a piece of thick plywood to work as a triangular wedge with hooks between the rods and a chair to match the bottom of the lens front. Be careful not to tension it down too much or you may break the camera or pull it around on its baseplate.
Last edited by robert Hart on Sat Jun 25, 2022 11:26 am, edited 1 time in total.
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Kim Janson

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Re: Questions about my camera, focusing and stabilization

PostSat Jun 25, 2022 11:23 am

The problem with most modern relatively low budget lenses is that they have no bearing on focus or zoom ring, it works fine when you hold it from both sides with your hand, but when applying pressure just from one side with the focus motor, not so well.

So it takes some custom build and 3D printing is very good for that. Applying force from both sides of the lens, or using a bit longer level etc. In general better attach the focus servo to lens body. As for loose bayonet, also something that easy to design and print 3D print part will fix well.

It will make though more difficult to change lens.

This was one experiment, the startup friction is always the problem, that makes very slow zoom difficult and starting smoothly viewtopic.php?f=4&t=66387&start=50#p438604 (the sigman 50-100 f1.8 is mechanically pretty good

This was mechanically bad lens, but works somewhat ok with normal servo with servo link that does not push the zoom ring to lens body, and it has separate lens encoder. (not most beautiful build though :) viewtopic.php?f=4&t=66387&start=50#p430760

Regarding lens control, the B4 lenses are totally from different planet. Very well build, everything moves smoothly.
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Last edited by Kim Janson on Sat Jun 25, 2022 11:36 am, edited 1 time in total.
LeViteZer Smooths the movement, www.levitezer.com
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robert Hart

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Re: Questions about my camera, focusing and stabilization

PostSat Jun 25, 2022 11:32 am

Further to my reply above, here is a link to the P+S Technik IMS-Mount product range. The flange face of the IMS-Mount base is 19mm, just a whisker under the 19.25mm of the M4/3-Mount system. It is likely that none of their offerings will suit your camera. The prices are rather gold-plated but the quality of their machine work is second to none.

https://www.pstechnik.de/products/ims-i ... t-adapters
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robert Hart

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Re: Questions about my camera, focusing and stabilization

PostSat Jun 25, 2022 11:55 am

This is a solution I arrived at for a heavy appliance which was stressing the lens mount on a video camera and binding the relay focus lens movement.

It comprises a one-piece saddle/chair. The construction material was phenolic-impregnated MDF electrical board. It is now an unused monument to some past best intentions.

If I made it again, I would split the piece around the cylindrical Letus body into a separate chair and saddle but I built this in a hurry with a holesaw, drill and round files.

Modern 3D printing tech and CAD design software would make this a breeze to build today.

Use the raise arrow on the right of image frame to see the fixture to the rods.
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robert Hart

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Re: Questions about my camera, focusing and stabilization

PostSat Jun 25, 2022 12:17 pm

Kim Janson. You are a braver man than I. Tearing into my Sigma 50-500mm to attach a Fujinon servo would terrify me. I chase aeroplanes with it so a servo would be handy.

Your lighter Sigma lens may be good internally but the big Sigma's scroll followers are plastic. The tiny screws attaching the scroll followers pull in their holes threaded into very thin concentric cylinders and tear the threads. The followers are not rollers but fixed pieces.

The front moving group is very heavy and a Fujinon servo would definitely stall especially if the lens was pointed upwards. That weight whilst facing upwards may be why one of the screws and scroll follower tore out and locked the lens up. I use it to chase aeroplanes in acrobatic flight.

It was full of fungus which is why I opened it up myself. I just about sent myself insane but I got there in the end
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wemrick1

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Re: Questions about my camera, focusing and stabilization

PostSat Jun 25, 2022 2:02 pm

I use the Tilta Nucleus Nano as well as the DJI RS2 focus motor and yes it can jostle when torqued. I can mitigate most of that by being gentle in the beginning movement of the focus motor moving the control wheel slowly to start. I would imagine adding a bracing strap to the end of the lens would help too. I haven't gotten around to that yet with the gimbal.
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Robdoc

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Re: Questions about my camera, focusing and stabilization

PostSun Jun 26, 2022 2:24 am

rick.lang wrote:General release of camera firmware 7.9 and the DaVinci Resolve 18.5 beta will work together. Can’t hurt to do the camera update and give it a go one the fifth beta of release 18. You would seem to have enough time to test right away and make a decision about using that approach for the the wedding. No pressure, eh? Bonne chance.

I use PD Movie currently for my focus control via a thumb controller on my rails. But I’m on a tripod when using it.

Sorry, one more thing Rick. I, of course have the full Davinci Resolve. When I go to download the DaVinci Resolve 18 Public Beta 5 Update it asks for all my info. Is that how you download the beta versions? Usually I get updates on new versions once I am in resolve. So, if I download this would I esentially have two resolves on my PC?
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rick.lang

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Re: Questions about my camera, focusing and stabilization

PostSun Jun 26, 2022 4:18 am

If you download the Resolve beta to a separate computer system (or booted from a separate macOS boot disk, it will be independent of your normal general release package.

If you booted on your system that has general release Resolve 17.4.x, it’s cleanest to remove that version and replace by 18.beta5.

I’m still on Resolve 17.4.x while editing the music festival footage for another week or so, but I’m eager to upgrade to Resolve 18 when I’m free of obligations.
Rick Lang
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Uli Plank

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Re: Questions about my camera, focusing and stabilization

PostSun Jun 26, 2022 8:27 am

I do all my testing of 18 from a separate boot. IMHO, the safest option not to mess with your daily work.
The software may be free, but the hardware needed for smooth performance is not.

Resolve Studio 17.4.6 , MacOS 12.3.1
MacBook M1 Pro, 16 GPU cores, 32 GB RAM
and
iMac 2017, Radeon 580, 32 GB RAM
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Jeffrey D Mathias

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Re: Questions about my camera, focusing and stabilization

PostSun Jun 26, 2022 9:54 am

Note too that DR18.5 will require updating your database... so back up.
AMD Threadripper 1950x 16-core 3.4 GHz
96 GB Crucial DDR4 2666 ECC UDIMM RAM
AsRock Fatal1ty x399 motherboard
AMD FirePro W8100 GPU & AMD Radeon Pro WX 8200 GPU
Windows 10 Pro 64-bit version 2004, build 19041.1165
DeckLink 4K Extreme 12G

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