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Old September 20th, 2008, 10:34 AM   #1
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Letus 35mm adapter, where to measure from?

Hi

Got a small job for this weekend. Think we're shooting with either HVX200 or Sony EX1, anyways, we're using a Letus 35mm adaptor, and I suddenly got a little confused.

Aren't I suppose to measure from the adaptor (where the picture gets projected on the rotating disc) or is that wrong, is it from the cameras chip I'm measuring?

Thanks
Allan
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Old September 20th, 2008, 03:17 PM   #2
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There is a separate subforum for Letus adaptors furthur down the list under Alternative Imaging Methods. The webmasters may move your thread to that subforum from here. In meantime here's a few comments.


Measure from the groundglass which is the 35mm focal plane.


The focal plane for the Letus Extreme is, according to the manual, 28.2mm from the front of the tube toward the main body.

If you have the optional support bracket, the rear face of this bracket, when correctly fitted under the tube, is the film plane.

The curved overhang of the support bracket when correctly mounted, faces forward of the support bracket upright and the front edge of the curved overhang matches the front edge of the tube body.

Camcorder iris sweet spot for the EX1's own lens / Letus Extreme achromat combination seems to be about f4 - f5.6. If you have a mattebox and ND filters, use them plus the camcorder ND, plus your choice of 35mm lens iris setting to try to keep the camcorder iris in the f4 -f5.6 zone. Be aware that for the EX1, a special achromat is needed. Optical image stabiliser in the EX1 must be selected off. Check for an orange colour cast in the blacks if using mattebox NDs other than Tiffen or Schneider.

If in doubt for exposure you may find it better to shoot under than overexpose with the EX1 because a hot image seems to lose sharpness.

Camcorder shutter should be 1/50th - 1/60th sec. 35mm lens iris should not be tighter than f5.6.

Autofocus on the EX1 will not track to the groundglass like the Z1 / FX1. Relay focus therefore must be set manually and often checked. The camcorder focus, when left on manual may be accidentally bumped. If you switch back to autofocus, the focus may drift.

Be careful not to pull the camcorder zoom too far wide. You may pick up an edge. If you can get hold of an underscanning monitor, use it. The widest zoom position you can use without bringing in an edge (vignette) will give you best apparent image sharpness.

You may already know all this so please forgive any repeated information.

Last edited by Bob Hart; September 20th, 2008 at 03:45 PM. Reason: error
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Old September 20th, 2008, 04:49 PM   #3
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Hi Bob

That was very very useful info. Cheers!
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