BMMCC PWM Specs

The place for questions about shooting with Blackmagic Cameras.
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Stu Aitken

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Re: BMMCC PWM Specs

PostTue May 10, 2016 8:49 pm

I only have Oly m43 lenses rigtht now but the micro seems to able to magically map the Iris on those to the full range of the servo channel - ie f1.8 is sitting around 5 degrees, and f22 close to the max

guess maybe its not as straightforward with the metabones adapter?

I did find I sometimes hit an awkward 'in-between' value where I could hear the lens almost flicking between one aperture and another, and its not easy to get around that using a consistent 'step change' in the servo angle each time I go up or down

so even though the full range on these lenses is mapped well automatically the 'steps' don't necessarily correspond perfectly with the limited precision of the 180 values the normal servo.write() method uses

I'm thinking if I continue with the PWM route I'll probably swith to using writeMicroSecond() instead which allows you to use much finer incremements (1000 vs 180) without resorting to any floating point variables
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Steve Watson

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Re: BMMCC PWM Specs

PostWed May 11, 2016 9:18 am

Hi,

that's interesting, I'd assumed that most lenses would act the same but I guess it depends on the iris servo in the lens itself.

What are the range of values for focus for those lenses ?

Steve
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Stu Aitken

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Re: BMMCC PWM Specs

PostWed May 11, 2016 4:14 pm

Steve Watson wrote:Hi,

What are the range of values for focus for those lenses ?

Steve


I haven't checked this thoroughly yet, mainly as its quite hard to tell from just looking at the lens whether you are actually at infinity or closest focus :)

on the list of things to check

I could get quite fine adjustments through using commands sent over a serial connection (not got it hooked up to any actual hardware yet, just driving over the serial port via USB from my macbook)
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Steve Watson

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Re: BMMCC PWM Specs

PostThu May 12, 2016 3:08 pm

Hi,

one thing I've discovered doing another shoot is that for these sort of stills lenses with a very small focus throw is that I need to do some kind of reverse logarithmic scale in my app's slider.

Just looking at the olympus 12-40 which has a rough servo values from 45 - 135 most of the range is taken up from 0.2 feet to 5 feet(looking at the lens marks in manual mode I'm estimating it's an angle of 70 degrees - which probably is servo values from 45 - 115) so it has only 20 degrees of movement from 5 feet to infinity which is not that great when you want to do a fine focus change from say 8 feet to 10 feet. This is of course exactly the same when using a manual follow focus on these sorts of lenses, but with a manual follow focus could just use a bigger cog to get finer control.

The exact logarithmic scale(ie to make the movement of the slider have more travel distance in the further focus distances) is probably completely different for every lens. So I'll have to experiment.

But on a gimbal the ability to do focus pulls using it is really useful - more the kind of focus pulls from one object to another, rather than a pull as you move in(at least in single user operation this is tricky, but then doing the same hand held might be equally as taxing.)

Steve
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Denny Smith

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Re: BMMCC PWM Specs

PostThu May 12, 2016 4:15 pm

Yes, the native MFT lenses have a short hard to control focus throw. I have tested the Panny Leica lenses, including the 42.5mm f/1.2, which has a longer focus throw, almost as much as the Zeiss ZF lenses, and can actually be focused with the LANC remote without too much problem. The other Panny Leica lenses perform fairly well too, with the 15m having the shortest focus throw. Assuming similar performance from the SBus, with a degree of greater control. Cheers.
Denny Smith
SHA Productions
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Stu Aitken

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Re: BMMCC PWM Specs

PostThu May 12, 2016 5:30 pm

isn't the focus throw on the Oly lenses perhaps different depending on how the clutch on the lens is set (for those that have this feature)?

eg if I engage the Manual focus clutch on the 17mm is obviously a quite short 90 degree throw, but I can also manually focus using the fly by wire with the clutch in the 'normal' autofocus position and the throw is much longer (albeit variable as its non linear dependent on speed of rotation)

I'm not sure if this also has an effect on doing it through the remote servo channel (which presumably would just ignore whatever the lens barrel clutch is set to anyway...)

LANC may be quite different as that is NOT sending an absolute focus position, just a command to focus nearer or further each time and there is no way to control the 'granularity of that - it must be something they have hard coded into the camera?
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Steve Watson

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Re: BMMCC PWM Specs

PostFri May 13, 2016 9:55 am

HI,

I can't speak for other lenses but the 12-40 only works with servo control if it it set to autofocus. If I set the lens so I can see distance marks it doesn't focus with my box.

Steve
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Stu Aitken

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Re: BMMCC PWM Specs

PostFri May 13, 2016 1:13 pm

that would make sense - I'm guessing the clutch effectively disengages the auto-focus motors completely then

the thing I could never work out is how it magically transfers the focus range to the absolute range on the manual clutch from the relative focus by wire system when you engage/disengage the clutch...

bringing this back to the main topic:

has anyone confirmed SBUS working with the actual camera yet?

I'm still working on it, but haven't quite got there yet - its quite a difficult protocol to deal with (stores 11 bits for each channel spread among multiple bytes, little endian bytes in big endian packet, inverted signal logic, etc) and I suspect the timing of sending each frame (and sending them repeatedly at regular intervals) is somewhat tricky to code for given the controller app also needs to read inputs from the user and then wrangle those into a valid signal
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Stu Aitken

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Re: BMMCC PWM Specs

PostSat May 14, 2016 5:04 am

eureka :)

SBUS works.

hints for anyone else trying (this may be gobbledegook for anyone unfamiliar with arduino land or RC electronics):

the various arduino libraries you can find online for sbus work with a little bit of adjustment - most of them are more aimed at reading sbus than writing it, but there is at least one that does writes as well

https://github.com/mikeshub/FUTABA_SBUS

(thanks to Mike Baker, et al)

I had to tweak the library a bit to get everything to work - I also got rid of lots of it that I didn't need (the read parts and some other RC functions like failsafe mode, etc)

you need to run the Tx out via a signal inverter to convert to inverted logic before running that to the camera Rx - eg http://www.maplin.co.uk/p/74hct14n-hct-cmos-logic-rs17t

I'll post more on all this later...

the camera doesn't seem to care much about the time between sbus frames which is a relief (I didn't have to mess about with difficult stuff like timer based interrupts or anything)

the 'switch mode' functions (ISO, shutter, WB and REC) work like this:

to go UP send a val on the associated sbus channel of 1024 followed immediately in the next frame with a val of 2046 - it won't work with either of the more obvious values of 1023 (neutral) or 2047(max)

to go down send 1024 then 0 in the next frame

the usable min and max for the more 'analog' like camera functions (focus, iris, levels, zoom) seem to be in a significantly smaller range than the possible min/max - my guess would be around half (so say 500 to 1500 aprox centred on 1023) - this seems different behaviour than PWM which did pretty much map the whole of the 'usual' RC servo control range available (ie 1000 to 2000 centered on 1500)) - this may be lens dependent though.

I'll try and make a video showing all of this tomorrow :)
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Kim Janson

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Re: BMMCC PWM Specs

PostSat May 14, 2016 7:08 am

Thanks Stu, good info*. I wonder though it the UP/DOWN limits are that tight. One should be able to use it also with normal SBUS RC transmitter, and the signal mapping on those probably is not that accurate or standard?

Will it not work if you go from about middle position to about 80% up or down?

*BMD, it would be good to have this kind of info on the users manual.
LeViteZer Smooths the movement, www.levitezer.com
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Stu Aitken

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Re: BMMCC PWM Specs

PostSat May 14, 2016 3:31 pm

Hi Kim

I'll do more tests on this and you may be correct - that it seemed to be really picky about the values could possibly be related to the fact my sketch is perhaps a bit all over the place in terms of the frame timing - I just tried to get it to work without worrying too much about how various part of the code that process input commands might have effected sending a very regular frame timing (or - maybe I lucked out and it is pretty much in spec and I'm overestimating the code execution overhead)

I found I had to put the 2 frames that did the UP/DOWN right after each other and I used a very guessed at delay of 6ms in-between (based on the supposed spec being a frame every 14ms or so and trying to guess how long the actual frame write took at 100k baud)

certainly last night it only stated working reliably when I did use those exact values on UP especially, but I'll see if I can get it to respond reliably to a wider range

the library I linked to seems designed for a controller that sits in-between a normal sbus receiver and whatever its controlling so it can also read a signal and pass that through, etc - you would probably want to keep a lot more of it intact than I did if running with real sbus gear in the mix
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Stu Aitken

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Re: BMMCC PWM Specs

PostSat May 14, 2016 3:45 pm

oh - one other thing that I expect may be important

I had to make sure that Serial() was set to 8E2 (ie one start bit, one parity bit and two stop bits for every 8bit data byte) as well as 100k baud - a lot of what I found in terms of existing arduino code seemed to omit that

I changed the serial initialisation that lives inside the SBUS class begin() method in the library cpp file to this


Code: Select all
Serial.begin(BAUDRATE, SERIAL_8E2);
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Stu Aitken

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Re: BMMCC PWM Specs

PostSat May 14, 2016 7:35 pm

Kim

ran some tests and here's what I found:

for switch mode camera functions:

the range of values you can use for LOW and HIGH are quite large - it even worked if I used 800 for LOW and 1200 for HIGH

however the acceptable value for the 'base' mid point seem to be much smaller - between 1024 and 1031 it worked anything outside of those nope - eg

going from 1030 to 1200 to switch up worked
going from 1032 to 2000 didn't

same on the way down - it seems you have to define the start 'Neutral' value pretty tightly then it will accept a drop or rise of any significant amount beyond the neutral to read it as an UP or DOWN on that camera setting

this was consistent amongst any assigned camera function

hope that helps - if thats still an issue you could easily capture the 'neutral' stick position you are using and just remap it?

eg:

Code: Select all
STICKPOSITION = map (STICKPOSITION, 900, 1100, 1024, 1030);


should do the trick - map() doesn't truncate out of band values so you can still use anything below 900 or above 1100 as valid inputs after
Last edited by Stu Aitken on Sat May 14, 2016 8:13 pm, edited 1 time in total.
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Stu Aitken

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Re: BMMCC PWM Specs

PostSat May 14, 2016 8:12 pm

I've uploaded my altered library and test sketch to git hub if anyone wants to take a look at it:

https://github.com/boldstelvis/BMC_SBUS

there will be a video to explain all later as well
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Marc Koecher

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Re: BMMCC PWM Specs

PostSat May 14, 2016 8:51 pm

Great work Stu. Sorry I somehow missed when this thread started taking off. I never got the notifications. But it looks like you've figured everything out. I've been away from playing with this for a while after having setup the gimbal controller. Hopefully getting back to it and creating a more elaborate controller/power/interface for shoulder mount setup.
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Stu Aitken

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Re: BMMCC PWM Specs

PostSat May 14, 2016 11:02 pm

cool - I'm planning something like the xc10 grip:

Image

initial layout idea:

https://drive.google.com/file/d/0B7XMok ... sp=sharing
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Kim Janson

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Re: BMMCC PWM Specs

PostSun May 15, 2016 6:15 am

This controller will get full control for BMMCC and a bit smaller gimbal for it too :)

https://www.facebook.com/levitezergimba ... 456697566/
LeViteZer Smooths the movement, www.levitezer.com
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Tony Rivera

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Re: BMMCC PWM Specs

PostMon May 16, 2016 9:25 pm

I'll pass along the suggestion to the teams in charge of the manual to see if that's possible.
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Max Buitrago

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Re: BMMCC PWM Specs

PostSun Jul 10, 2016 5:58 am

Stu, I have the BMMCC mapped to my Taranis remote through SBUS and I cannot get these microsecond values to work correctly. for example the Rec on a 3 position switch, all it does is start recording with any input value. I have center at 1030 - UP 1200 and DOWN 0 but when I hit the switch to either position it starts recording and it does not stop even bringing it back down 0

Any one here trying it out with an RC remote?

Max
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Stu Aitken

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Re: BMMCC PWM Specs

PostTue Jul 12, 2016 6:40 pm

Max Buitrago wrote:Stu, I have the BMMCC mapped to my Taranis remote through SBUS and I cannot get these microsecond values to work correctly. for example the Rec on a 3 position switch, all it does is start recording with any input value. I have center at 1030 - UP 1200 and DOWN 0 but when I hit the switch to either position it starts recording and it does not stop even bringing it back down 0

Any one here trying it out with an RC remote?

Max


record works a bit differently in that any defined 'signal' will trigger on/off

in the case of sbus that would be any change from defined neutral to low or high
as I mentioned before the camera seems quite picky about what it accepts as "neutral" over sbus (in my previous tests that's strictly values between 1024 and 1030 only) which might tbe the issue?

there is apparently no defined "ON" and separate "OFF" signal for record - it will just change state each time from whatever its doing
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Kim Janson

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Re: BMMCC PWM Specs

PostTue Jul 12, 2016 6:52 pm

Yes, the current recording control is simply just bad implementation, BMD please fix it.

SBUS level up=record
SBUS level down=do not record

would work just fine.
LeViteZer Smooths the movement, www.levitezer.com
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ChrisBird

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Re: BMMCC PWM Specs

PostSun Sep 09, 2018 12:36 pm

I've been working on mine through a Taranis 9XD+ and I could only get the switch items to work if the neutral position was 1002.

I agree its kinda annoying in its current implementation.
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ChrisBird

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Re: BMMCC PWM Specs

PostThu Sep 27, 2018 7:18 am

ChrisBird wrote:I've been working on mine through a Taranis 9XD+ and I could only get the switch items to work if the neutral position was 1002.

I agree its kinda annoying in its current implementation.


After discussion with Black Magic support team even though the change notes dont indicate any changes after the version of firmware I have it appears to have resolved the issues.

Center is now considently 1514 PWM on SBUS. The doco has also been updated to explain how it works for each of the different controls. I'm very happy with it.
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