Pl to Ef mount URSA 12K

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thefilmaddict

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Pl to Ef mount URSA 12K

PostWed Dec 01, 2021 12:26 pm

Because the other video out there seems to have some wrong information in it, I decided to make a video documenting how to change the pl mount to an ef mount on the Blackmagic URSA 12k. Thanks to the help you guys provided on the forum, I think I got it right. As always, I appreciate your knowledge and I am now able to use my ef glass.

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rick.lang

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Re: Pl to Ef mount URSA 12K

PostWed Dec 01, 2021 7:32 pm

Good job! What was the total thickness of the shim(s)?
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Jeffrey D Mathias

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Re: Pl to Ef mount URSA 12K

PostThu Dec 02, 2021 12:02 am

Seems this video is missing something as well. According to BMD instruction card included with the PL mount there is a 0.10mm shim that is taken away when changing from PL to EF and added when changing from EF to PL mount. It also states to make sure to always leave the remaining 0.10 and 0.50 shims when removing the EF and that they always stay with the camera.

So even though a nice looking video, it is however miss-informative (also seems to spend more time concerning the torque wrench than the mount.) Please refer to official BMD information.

By the way BMD also suggests to place the camera vertically when changing mounts... maybe so the shims do not fall out when removing the mount.
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Uli Plank

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Re: Pl to Ef mount URSA 12K

PostThu Dec 02, 2021 12:09 am

Well, position has its pros and cons. If you put it vertical, there as higher risk of dust falling into it. I had no problem with the shims keeping it horizontal.
Regarding the shims to keep or take out, many EF lenses have far less precision than PL. You never know before trying a proper collimation.
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timbutt2

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Re: Pl to Ef mount URSA 12K

PostThu Dec 02, 2021 4:47 am

Jeffrey D Mathias wrote:Seems this video is missing something as well. According to BMD instruction card included with the PL mount there is a 0.10mm shim that is taken away when changing from PL to EF and added when changing from EF to PL mount. It also states to make sure to always leave the remaining 0.10 and 0.50 shims when removing the EF and that they always stay with the camera.

So even though a nice looking video, it is however miss-informative (also seems to spend more time concerning the torque wrench than the mount.) Please refer to official BMD information.

By the way BMD also suggests to place the camera vertically when changing mounts... maybe so the shims do not fall out when removing the mount.

1st: It has been confirmed with Hook that the 0.10mm Shim can remain in going from the PL to EF mount with either the 12K or earlier 4.6K sensor UMP cameras. This more than likely does have to do with EF being less precise than PL. But Hook said you can leave the 0.10mm Shim be.

2nd: And, I've changed my mount countless times horizontally without issue. I usually stick it on a tripod head in a high hat, position all my tools on the work bench, and do the change.
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Travis Hodgkinson

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Re: Pl to Ef mount URSA 12K

PostThu Dec 02, 2021 4:59 am

Yea pretty sure the 0.1 stays in when going from either mount type.
Not sure why you’d need the other shins then.
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rick.lang

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Re: Pl to Ef mount URSA 12K

PostThu Dec 02, 2021 6:29 am

When I changed from my URSA Mini 4.6K PL mount to my UMB4 mount recently, the zoom was perfectly parfocal with 0.50+0.20 shims. With only 0.50+0.10 shims, focus wasn’t parfocal. Adjusting the back focus on the Fujinon was insufficient unless the correct shim was added.

I usually change mounts with the camera at about 5-10 degrees to help support multiple shims.

Avoid changing the mount with the camera vertical as has been stated above so nothing falls onto the sensor glass: dust, flakes of skin, screws, etc.
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Travis Hodgkinson

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Re: Pl to Ef mount URSA 12K

PostThu Dec 02, 2021 9:36 am

Are the shims purely there to ensure the markings on your lens are accurate when pulling focus?
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Uli Plank

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Re: Pl to Ef mount URSA 12K

PostThu Dec 02, 2021 10:32 am

It’s about parfocal zooming too.
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Travis Hodgkinson

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Re: Pl to Ef mount URSA 12K

PostThu Dec 02, 2021 10:46 am

An I see.
So if you’re using primes it just comes to the Accuracy of markings?
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rick.lang

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Re: Pl to Ef mount URSA 12K

PostThu Dec 02, 2021 9:33 pm

And to ensure you can focus to infinity at the infinity witness mark (for those who are fortunate enough to be able to see the horizon).
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Howard Roll

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Re: Pl to Ef mount URSA 12K

PostThu Dec 02, 2021 11:50 pm

Travis Hodgkinson wrote:An I see.
So if you’re using primes it just comes to the Accuracy of markings?


If there are too many shims then wides won’t hit infinity. There are additional optical costs when attempting to front focus back focus problems, primarily softness.

Good Luck

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