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Arri BL3 and Super35mm Help...


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#1 Todd Anderson

Todd Anderson
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Posted 28 September 2007 - 03:43 PM

Hello,

I was wondering if anyone can shed some light on the particulars of converting and/or the shooting of 4-perf Super35mm with an Arri BL3.

In short, my questions are: (A) what are the limitations and quirks involved in shooting Super35mm with a silent/full aperture gate, 'without' the re-centering of the PL mount/flange? And (B'), what is required and how difficult is it to re-center the PL mount/flange on a Arri BL3 if Option A, above, is too limiting and/or I wanted the peace of mind of having a 100% spec camera? And if we are talking anything over two, three, or four thousands dollars here for the re-centering, I'll probably happily forgo peace of mind for now :-) ....

As I understand it from reading Jon Fauer's Arriflex 35 Book, later model BL's?I'm assuming the 4 or 4s's?required three small modifications when shooting super 35mm (after the obvious step of swapping out the academy gate for a silent/full aperture gate) The three changes were:

1) re-centering of the PL mount my removing the six cheeshead screws in the flange and rotating the flange 180 degrees. Which I imagine re-centered the mount because the new holes were such that they slightly shifted the offset back to the center, be that 2 mm's, or what have you.

2) unscrew the video tap flange and turn the video tap 180 degrees, which I assume has a similar effect as what takes place on the re-centering of the PL mount.

3) re-centering of the base plate tripod mount slightly.


From what I can tell my particular BL3 (recently purchased from a rental house in Canada via an acquaintance) has a silent/full aperture gate installed. I can't tell if the mount has been re-centered, though my guess is that is has not. I say this because the camera came with a academy 1:33 ground glass inside it with cross hairs centered for academy. So, I can only assume that unless someone just kind of through that ground glass in there to have something in place for the sale, the last way it was used was academy 1:33 with a silent aperture. I should also mention that my BL3 has a wide-angle eyepiece. So I can see all of the full frame aperture through the viewfinder, albeit the left two corners are slightly obscured do the limitations of the viewfinder. Though, I think for 1:85 and 2:40 extraction I would be fine for framing.

So after I take care of the first hurdle, that of putting a proper Super35mm ground glass into place? say one with a re-centerd crosshair with Super 1.85mm markings for center extraction?what problems would I run into optically and otherwise by not re-centering the mount?
I made two assumptions myself, which are just that, assumptions. But here they are:

1) I assume seeing how the mount is not re-centered, I would need make sure that any lenses that barely covered Super35mm as it were, would not be vignetting on left side of the frame. Hopefully this may just be a small problem, especially with primes.

2) I also would imagine with a zoom, I may run into problems with the image 'pulling' to one side during any zooming that may take place. And I imagine any lenses that breathed a lot would encounter similar traits. Though it seems zooms seem to take on these traits to some degree as they are.

Any other problems here by the non re-centering of the mount? The plane of focus remains the same regardless of leaving the mount at academy or re-centering, correct? Any other quirks?

And I guess lastly, if there are too many anomalies that I would encounter by not re-centering the mount, how difficult is it to re-centered the PL mount on a BL-3? Could a technician rotate the PL flange 180 degrees, carefully drill six new holes that are slightly offset by 2 millimeters, or what have you, and that would be that? Or are we opening up a can of worms here and it is best to shoot Super35mm with the silent gate in place and the slight quirks that may be involved with the non-re-centering of the mount?

Any help or insight appreciated in advance.

Todd
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#2 Todd Anderson

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Posted 28 September 2007 - 11:31 PM

I just realized another anomaly of not having a exactly centered lens: any lens that does not have a natural perspective, like say a wide-angle lens, or a lens prone to other distortions like 'barreling' or 'pin-cushioning', say on a zoom, would have a slightly off-center effect of such distortions.

I suppose it could look a bit disconcerting with one side of the frame 'barreling' to more of a degree, or from a different starting point, than the other side of the frame. For example.
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Glidecam

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Visual Products

Wooden Camera

Rig Wheels Passport

Aerial Filmworks

Opal

Broadcast Solutions Inc

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