Thread: BMMCC with a v mount converter?

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  1. #91  
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    The AC house wiring was an example of how some separation schemes might work, was not referring to AC-DC power supplies. But yiu are correct I that transformers can provide true power tap separations.
    Cheers
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  2. #92  
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    Here is my attempt to hack SmallRig and build a rear mounting plate. Probably cheapest and most functional possible. Rear plate can be adjusted to use with or without LP-E6 backup battery. Total weight 450g (2x Cheese Plates, 5x RailBlocks, 2x 6inch Rods, 10x screws). If you use long Arca Swiss or Manfrotto QR plate, you can screw it directly to the RailBlocks and bypass bottom Cheese Plate.
    Each item sold as a separate part, so you got a lot of different bonus screws, hex keys and large rugged ziplock bags. Probably i will replace middle Ratchet Wingnut screws with regular hex screws because they are more usable in limited space.

    2pcs SmallRig Mounting Cheese Plate 1598
    8pcs SmallRig Super lightweight 15mm RailBlock v3 942
    2pcs Aluminum Alloy Rod 6inch 1050






    Last edited by shijan; 12-02-2017 at 05:27 PM.
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  3. #93  
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    I really like how smooth everything looks together there shijan. Really keeps it compact. The only downside is that there isn't a QR plate to get the camera off the rails quickly. But I guess that'd cost more and make it harder to fit together.
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  4. #94  
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    Quote Originally Posted by Ryanite View Post
    I really like how smooth everything looks together there shijan. Really keeps it compact. The only downside is that there isn't a QR plate to get the camera off the rails quickly. But I guess that'd cost more and make it harder to fit together.
    Yea, you are correct but it appears not too complicated to unscrew 4 screws if needed. Also QR plate between camera and rails adds about 2-3cm of of additional height. If use Follow Focus rods are usually permanently attached to camera all the time.
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  5. #95  
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    If you put 15mm spuds on the corners of the Smallrig Easy Plate thusly

    Easy Plate.jpg

    Then attach a pair of these, cool mounting block (Smallrig) 980s. Creates 2 mounting points 18mm on center.

    cool mounting block 980.jpg

    Then you can attach the smallrig V-Mount plate like so. You can also mount another Easy Plate if you wanted but you'd need to drill out and countersink a pair of the 1/4-20s.

    V-Mount.jpg

    Mine is inverted to attach to the rod risers for bringing the camera and lens up to 85mm on center. If you have a smaller setup or don't use rails install the spuds on top of the plate.

    Camera Legos, good times.
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  6. #96  
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    Why is it important to have the camera up to 85mm? Is it for large cinema lenses?
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    Quote Originally Posted by Stelvis View Post
    see I never understand this idea- and it may very well just be me being ignorant - but how do you exactly 'isolate grounds' when they will end up at the same contact terminal on the battery one way or another?

    can someone explain how this works in more detail?
    Ok, first you need to understand the cause of the problem before you can understand how it's solved.

    So, what IS the cause of the problem? It's unwanted electromagnetic radiation that induces signal into your equipment and signal carrying cables. Each electrical device and signal carrying cable (video and/or audio) needs a 'shield' to protect it from this unwanted electromagnetic radiation, otherwise known as RFI (radio frequency interference). RFI is all that radio signal present pretty much everywhere we go, especially in high population densities. You will also find electromagnetic radiation from power circuits in houses/buildings which can induce unwanted signal. The reason RFI affects signal cable is because video and/or audio signals are very low voltage/amperage and therefore susceptible. So the shield 'captures' this radio rubbish and sends it to 'ground'.

    In a 'grounded' device, it's sent to earth - which is a copper/metal rod physically driven into the ground (dirt!). In this situation earth loops can be caused if you are powering devices (that themselves are connected together, such as an audio cable connecting and audio system and camera) from different power points. Each power point may have a different earth voltage (resistance or differential) on the earth pin than the next, so RFI may be captured by the audio cable shield, and then 'earthed' from one device to another instead of straight to ground. In otherwords, electricity takes the path of least resistance, so if one power point earth pin has less resistance than another, the RFI will pass up that audio cable and through the device, inducing 'noise.'

    In a battery powered system - not connected to mains power, or earth - RFI can still induce noise into signal if there's different earth voltages on the equipment. For example, a micro camera and VA 5". They are connected via an HDMI cable, so therefore the earth shields are connected together. If there's a differential between the earth shield, then an earth loop is conducted. So effectively you need to 'isolate' each the equipment's earth from each other, and one effective way is to use a transformer isolator.
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  8. #98  
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    Quote Originally Posted by Ryanite View Post
    Why is it important to have the camera up to 85mm? Is it for large cinema lenses?
    No, it's just the 15mm LWS-light weight standard, it's 85mm vertically from rod center to lens center just like all LWS rails are 60mm horizontally. Historically a lot of gear is designed with this in mind, any Chrosziel, Arri, Oconnor, etc., matebox isn't going to be compatible with a lens/camera combo that doesn't follow. My camera lens is at 85mm on center so that it works with the Chrosziel matte box that I have. There are a couple other "standards" for 19mm and studio configurations but I don't know the differenced off the top of my head.

    Good Luck
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  9. #99  
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    Quote Originally Posted by trispembo View Post
    Ok, first you need to understand the cause of the problem before you can understand how it's solved.

    So, what IS the cause of the problem? It's unwanted electromagnetic radiation that induces signal into your equipment and signal carrying cables. Each electrical device and signal carrying cable (video and/or audio) needs a 'shield' to protect it from this unwanted electromagnetic radiation, otherwise known as RFI (radio frequency interference). RFI is all that radio signal present pretty much everywhere we go, especially in high population densities. You will also find electromagnetic radiation from power circuits in houses/buildings which can induce unwanted signal. The reason RFI affects signal cable is because video and/or audio signals are very low voltage/amperage and therefore susceptible. So the shield 'captures' this radio rubbish and sends it to 'ground'.

    In a 'grounded' device, it's sent to earth - which is a copper/metal rod physically driven into the ground (dirt!). In this situation earth loops can be caused if you are powering devices (that themselves are connected together, such as an audio cable connecting and audio system and camera) from different power points. Each power point may have a different earth voltage (resistance or differential) on the earth pin than the next, so RFI may be captured by the audio cable shield, and then 'earthed' from one device to another instead of straight to ground. In otherwords, electricity takes the path of least resistance, so if one power point earth pin has less resistance than another, the RFI will pass up that audio cable and through the device, inducing 'noise.'

    In a battery powered system - not connected to mains power, or earth - RFI can still induce noise into signal if there's different earth voltages on the equipment. For example, a micro camera and VA 5". They are connected via an HDMI cable, so therefore the earth shields are connected together. If there's a differential between the earth shield, then an earth loop is conducted. So effectively you need to 'isolate' each the equipment's earth from each other, and one effective way is to use a transformer isolator.

    Prove it. Take 5 minutes with a multimeter and prove there is any way possible to isolate the ground between a micro and a monitor, you can't because the IO is chassis grounded. All you can do is isolate the battery from the transformer and most transformers don't do this.

    The "problem" is people wanting to find a JFK style magic bullet that explains a host of different problems across multiple OEMs which are poor transformer design, mismatched cables, and poorly designed circuits, or rather circuits that were designed for 10w suddenly having to deal with 200+w from a pro battery rather than a tiny transformer. Some dude came up with the idea of ground loop and people ran with it because it sounded good. I can't pretend to know all the permutations off all the historic failures though Tilta, and BMCC are the usual suspects and come up often. As far as the scope of this thread, which is the micro and V-mount batteries, ground isolation is physically impossible, battery, transformer, or otherwise.
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  10. #100  
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    Quote Originally Posted by Howie Roll View Post
    Prove it. Take 5 minutes with a multimeter and prove there is any way possible to isolate the ground between a micro and a monitor, you can't because the IO is chassis grounded. All you can do is isolate the battery from the transformer and most transformers don't do this.
    Ah yes, Howie, right you are. In the example I was discussing each device has it's own battery, but as this thread is about a single V-lock battery, I'm just waffling.

    So, the problem is the same - unwanted noise induced into the signal - but the solution is different. With a single battery system isolating each device will only go so far.

    In a DC power supply, the noise will need to be suppressed with filtration - high frequency series choke or high frequency suppressor. It's like a low pass filter and will usually filter out everything marine frequency and above (roughly 100MHz +). In a standalone camera with using one battery with multiple devices in one (IE. URSA Mini - camera, monitor, audio preamps, etc) these power problems are solved by the electrical engineers. But in a third party power distribution system - one battery powering multiple devices - as Denny, Howie and others have mentioned, it's going to depend on the quality of the design. A better design will have high frequency suppressors built in, along with quality voltage regulators etc. Cheaper distribution systems, such as Tilta's and others, probably not.

    A typical high frequency suppressor is the little box that comes with your ADSL modem. It sits between your modem and the telecom line running into your house/office/building. One could try inserting that on the DC line powering one or all devices. Though I suspect there are some purpose built products for the applications discussed in this thread - powering a BMMCC & Monitor for a single V-lock battery.
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