PCC 6k + Sigma 18-35mm F1.8 DC HSM: Camera can go to F1.7?

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aBavarian Normie-Pleb

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PCC 6k + Sigma 18-35mm F1.8 DC HSM: Camera can go to F1.7?

PostWed Jul 27, 2022 4:26 am

Hello everyone,

I hope I'm not asking an ignorant question, this is on one hand my very first Blackmagic camera and on the other hand my first Sigma lense.

I'm using a Pocket Cinema Camera 6k with the popular Sigma 18-35mm F1.8 DC HSM lense, image quality-wise I'm pretty happy but I noticed something (to me) weird in the camera settings:

The camera's firmware control for the lense goes to F1.7 and not just F1.8.

Is this...

- Normal?
- A bug?
- A hint that something might be broken?

What I've tried without any effect:

- Updated camera to latest firmware with camera software package 7.9
- Reset camera firmware to factory defaults
- Checked that the lense has the latest firmware (2.03) with the Sigma USB Dock
- Reset the lense firmware to factory defaults

Thanks for you guys' help!

Regards,
aBavarian Normie-Pleb
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aBavarian Normie-Pleb

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Re: PCC 6k + Sigma 18-35mm F1.8 DC HSM: Camera can go to F1.

PostWed Aug 03, 2022 7:38 pm

A small update: No changes of the situation with 7.9.1.

But I've heard from other Blackmagic camera users that they've also seen this with the Sigma 18-35 Art lense.
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Uli Plank

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Re: PCC 6k + Sigma 18-35mm F1.8 DC HSM: Camera can go to F1.

PostFri Aug 05, 2022 7:12 am

Nothing broken. Communication error, I suppose.
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rick.lang

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Re: PCC 6k + Sigma 18-35mm F1.8 DC HSM: Camera can go to F1.

PostFri Aug 05, 2022 4:05 pm

In a post from BMD, we were told that BMD is reporting the aperture sent by a lens whereas other camera manufacturers may round the value to the lens manufacturers’ published specs.
Rick Lang
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Howard Roll

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Re: PCC 6k + Sigma 18-35mm F1.8 DC HSM: Camera can go to F1.

PostFri Aug 05, 2022 10:02 pm

rick.lang wrote:In a post from BMD, we were told that BMD is reporting the aperture sent by a lens whereas other camera manufacturers may round the value to the lens manufacturers’ published specs.


I’m not so sure. The situation with broadcast lenses isn’t any better.

viewtopic.php?f=4&t=165391

Good Luck
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aBavarian Normie-Pleb

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Re: PCC 6k + Sigma 18-35mm F1.8 DC HSM: Camera can go to F1.

PostSat Aug 06, 2022 1:44 am

Since the combo Sigma 18-35 F.1.8 + PCC 6k is so popular I'm wondering why this hasn't been addressed with firmware updates (on either side, Sigma or Blackmagic, but my gut says it's a BM issue).

A weird thing is that it doesn't just seem to be a displayed value bug (for example no change between the setting F1.8, the actual lense's limit and F1.7 what the camera thinks to be doing), if I carefully watch thhe histogram I can see that there actually is a slight difference between F1.8 and F1.7.

In the meeantime I've tried actually reflashing the camera firmware (coming from a computer background so I get the need for firmware resets to address bugs) which led to the camera stil going to F1.7 manually BUT now if I select automatic Iris control via the camera firmware it only goes to the correct F1.8 - which is probably F1.9 since there still is the slight noticeable difference between F1.8 and the manual F1.7.

For a new customer this doesn't especially invoke trust in the camera and is honestly speaking embarassing :-/
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Mike Potton

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Re: PCC 6k + Sigma 18-35mm F1.8 DC HSM: Camera can go to F1.

PostSat Aug 06, 2022 3:28 am

It just doesn’t matter if there is a .1 rounding difference.
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carlomacchiavello

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Re: PCC 6k + Sigma 18-35mm F1.8 DC HSM: Camera can go to F1.

PostSun Aug 07, 2022 12:58 pm

The same with pocket4k and metabone, on ursa g1, on 6k, on Sony with adapter sacked falcon lite, on x-t4 with fringer adapter.
May be sigma that send it.
All work fine what is a matter? :-)


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rick.lang

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Re: PCC 6k + Sigma 18-35mm F1.8 DC HSM: Camera can go to F1.

PostSun Aug 07, 2022 1:42 pm

Howard Roll wrote:
rick.lang wrote:In a post from BMD, we were told that BMD is reporting the aperture sent by a lens...


I’m not so sure. The situation with broadcast lenses isn’t any better.

viewtopic.php?f=4&t=165391


Thanks, Howard. I suspect failing to close the iris completely may be a different and more serious issue. My manual Fujinon Cine Zoom iris will close completely.
Rick Lang
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Uli Plank

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Re: PCC 6k + Sigma 18-35mm F1.8 DC HSM: Camera can go to F1.

PostSun Aug 07, 2022 1:46 pm

Most lenses don't close completely, it's normally a feature of broadcast lenses.
The software may be free, but the hardware needed for smooth performance is not.

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Howard Roll

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Re: PCC 6k + Sigma 18-35mm F1.8 DC HSM: Camera can go to F1.

PostSun Aug 07, 2022 9:18 pm

So why are BM cameras rounding down when everyone else is rounding up? Or is it that BM cameras aren't rounding at all and simply truncating so f1.785 becomes f1.7 rather than f1.8? Yeah agreed, with photo lenses it's no big deal but when you're working with broadcast tools this sloppy math can have major consequences. ENG lenses you can just grab the ring and close it, with box lenses there's no external physical iris or zoom control and they rely on properly calibrated signals which the BM units do not provide.

Good Luck
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roger.magnusson

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Re: PCC 6k + Sigma 18-35mm F1.8 DC HSM: Camera can go to F1.

PostSun Aug 07, 2022 11:24 pm

Something's not right. The BMD post Rick mentioned was in reply to my question about Olympus lenses on the Pocket 4K showing a higher f-stop, not lower. It's consistently reported as +0.1. This started with firmware 7.9.

Seems there's more to it than the explanation we have so far. Maybe they are rounding up when it's below 0.05 and truncating when above 0.05.
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rick.lang

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Re: PCC 6k + Sigma 18-35mm F1.8 DC HSM: Camera can go to F1.

PostMon Aug 08, 2022 12:32 am

Agree both issues need to see a resolution with the issue affecting box lenses especially important to get right in the camera.
Rick Lang

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