Blackmagic Forum

Hi!

The question is basically in the title. With the new bmcc6k being in L mount, I wondered if it was possible to use the most recent sigma art lenses which are normally in focus by wire and switch them to linear focus (like you can do with the lumix s5iix for example).

If any of you guys knows the answer it would be of great help
Thanks

Sigma ART HSM L-Mount lenses including their 24-70mm can focus manually as well as by wire… just rotate the focus ring.

Rick I think some of the newer mirrorless-only models are focus by wire even if you use the ring as they specifically mention linear/nonlinear focus in the marketing copy. Or, alternatively, if one was using a Panasonic lens that is definitely always by wire is that an option? I don't see anything in the manual, and I'd bet this is something that has not and will possibly never be implemented.

Jon, I’m not sure what is happening inside the lens housing when one rotates the focus ring manually on those new Sigma L-mount lenses, but I don’t think there’s any limitations on which camera those new lenses are used as long as it’s L-mount. Or if an electrical contact is required to operate the lenses on a camera without electrical contacts if such a thing exists. But that may not be a concern given the BMCC6K L-mount is active.

It's not whether they work at all, it's whether you can switch between speed sensitive and linear focusing. Most focus by wire implementations are speed sensitive so you don't get consistent focus throws, but companies have started to make it so you can switch the focus sensitivity and whether it's linear or not, sometimes along with focus direction and total rotation from MFD to infinity.

I'm sure the lenses work on the BMCC6K, it's just whether you have access to the linear focus setting (or if it's on by default, which would be great.)

Thanks for clarifying that for me. I think my brain is a little exhausted but no rest for the wicked.

Here is a video that specifically addresses the manual focus of the BMCC6K using an L-mount lens:



According to this reviewer’s early impressions, use a manual fine tune of the focus may be problematic compared to the more predictable behaviour with his Panasonic camera’s settings that does address linear manual focus. He hopes BMD will update the camera firmware to offer a similar setting when using the focus ring manually.

Better yet use fixed position on a non linear curve. Here’s a cap of an 18mm CP3. With manual lenses the bulk of the mechanics are dedicated to close up work. It’s a funtion of how optics work. With this lens 180 degrees of focus travel are dedicated to a 1 foot range from 13” to 25” and from 5’ to infinity you’re only working with about 20 degrees. It would be a cool feature to invert the physical characteristics of the lens and make the long end a little more granular.

Good Luck

Howard Roll wrote:Better yet use fixed position on a non linear curve. Here’s a cap of an 18mm CP3. With manual lenses the bulk of the mechanics are dedicated to close up work. It’s a funtion of how optics work. With this lens 180 degrees of focus travel are dedicated to a 1 foot range from 13” to 25” and from 5’ to infinity you’re only working with about 20 degrees. It would be a cool feature to invert the physical characteristics of the lens and make the long end a little more granular…

I agree with this novel concept, Howard. My shoot last weekend needed to cover a stage area over 20m away and roughly up to 15m deep. My last focus mark is 20m on the Fujinon and I set the PD Movie focus thumb control to move about 300 degrees while the lens itself moves about a degree. Would be wonderful to have a setting on a lens that allowed longer throws for the farther focal distances. Three cheers for the PD Movie giving me that long focus throw.

Howard Roll wrote: It would be a cool feature to invert the physical characteristics of the lens and make the long end a little more granular.

This is possible with modern follow focus systems from Preston and Arri.

“ The focus scale can be expanded or compressed by finger touch”

https://prestoncinema.com/products/product-info/hu4

“ Focus mapping to pre-marked rings uncouples focus scales of a lens from the focus ring of the handset and allows you to choose the best scale for your shooting situation (also: no focus rings have to be made during prep).”

https://www.arri.com/en/learn-help/lear ... system-faq

JB

Back on topic though!

Has there been any development or mention of something in the works to set manual focus options?

As stated in the review Rick linked to, other cameras can already switch between between linear & non-linear and/or set the ring rotation angle for linear focus.

Would love to know this before investing in a lens that might not be able to switch to linear focus...

BramSmans wrote:Back on topic though!

Has there been any development or mention of something in the works to set manual focus options?

As stated in the review Rick linked to, other cameras can already switch between between linear & non-linear and/or set the ring rotation angle for linear focus.

Would love to know this before investing in a lens that might not be able to switch to linear focus...

I also really would like to know this and can't find information anywhere. But probably will find out this week. BMCC6K and Sigma 24-70 Art II L-Mount should arrive this week.

FYI There is now way as I can see, that allows for changing between linear and adaptive focus of the Sigma Lens with the BMCC. But it seems quite linear as far as I can tell.

After trying it with the Focus Pro from DJI now, I must say that it is not linear by default and I don't find any way to change it in the camera. And according to the information I found the switch is only to be found in the camera menu.

We don't support linear focusing with L-Mount lenses at the moment, but this is something we're looking to add.

Thanks for the official reply!

Yes thank you for the reply! You would add so much value to the Sigma L Mount lenses, that support linear focus switching!

It would be great to have the feature. But what I’m delighted with here is an actual response from someone inside of BMD who’s telling us both that they’re aware of the request, agree that it currently can’t be done, and are working toward a solution.

We get almost none of this in the Resolve forum. We’re told it’s BMD policy to not interact in this way.

Joe Shapiro wrote:We get almost none of this in the Resolve forum. We’re told it’s BMD policy to not interact in this way.

BMD generally don’t talk about what’s in the future. They don’t do roadmaps or talk about the direction they’re going.


JB

John Brawley wrote:

Joe Shapiro wrote:We get almost none of this in the Resolve forum. We’re told it’s BMD policy to not interact in this way.

BMD generally don’t talk about what’s in the future. They don’t do roadmaps or talk about the direction they’re going.


JB

Believe me I know! I just think it’s taking it a bit too far when they won’t talk about if what behavior is already there is a bug or as intended, and if the former do they have any intention of fixing it in the near future.

John Brawley wrote:BMD generally don’t talk about what’s in the future. They don’t do roadmaps or talk about the direction they’re going.


JB

True, with the only exception perhaps with that possibly unplanned leak for the immersive (stereo) camera.

Introducing Blackmagic URSA Cine Immersive
https://r.tapatalk.com/shareLink/topic? ... source=app

Joe Shapiro wrote:

John Brawley wrote:

Joe Shapiro wrote:We get almost none of this in the Resolve forum. We’re told it’s BMD policy to not interact in this way.

BMD generally don’t talk about what’s in the future. They don’t do roadmaps or talk about the direction they’re going.


JB

Believe me I know! I just think it’s taking it a bit too far when they won’t talk about if what behavior is already there is a bug or as intended, and if the former do they have any intention of fixing it in the near future.

It’s cultural and with some good reason.

Lots of companies work this way (Apple comes to mind)

JB

John Brawley wrote:
It’s cultural and with some good reason.

Lots of companies work this way (Apple comes to mind)

JB

BMD did publish a road map with the Big Ursa and its swappable sensor claim also the Ursa Mini 4.6k OG with its Global Shutter option all ended up being tall tales. I guess lesson learnt.

Back on topic (AGAIN)...


i really like what Samyang have done with their V-AF series lenses. They can be used linear, but they won't be 100% accurate. Which is what I'd suspect for other focus-by-wire lenses switched to 'linear', too. Pull focus from A to B a few times and end points will be off.

For that reason Samyang separately sell a manual (follow-) focus adapter that snaps to the front of the lens and turns it into full manual.

https://samyangus.com/products/v-af-man ... us-adaptor

Now, I am not sure about linear performance of other focus by wire lenses, maybe there are some that are 100% precise? Are there any focus-by-wore lenses that actually perform 'stable' when soft-switching to linear?