Bob Hart

Ted.

At the back of the Letus Extreme flip enclosure, there is an achromat, fastened in conventional optical practice inside an approx 8mm shoulder with a threaded ring. Its rim sits just inside the shoulder.

The various adaptor rings with their filter threads slip onto this shoulder and secure with three radius screws.

The depth of these rings and thus the setback of the camera from the Extreme varies for different filter thread diameters. The achromat would have to be removed from withn the Letus Extreme housing to move it to the front of the Fujinon lens.

I'm not sure about recommending this as any warranty open to him relating to the Letus would be voided.

When you removed the plastic ring out of the front of the Fujiono lens, did you find a 72mm diameter filter thread inside the rim?

I have observed two styles of lens attached to the JVC HD100 camera, both Fujinon. I did not study them closely.

One of Steve Rice's Fujinons looks like it either has no plastic ring or that it has been removed or fallen out. I did not study it to see if there was an internal thread there and have no opportunity to study it before I see it next.

If there is a 72mm thread, this raises a few options for experiment over here.

I have the 82mm ring so this would fit up to a JVC GY-HD100 standard Fujinon as I know it. I also have a 4+ and 7+ achromat which will fit up to a 72mm internal thread. I could do a limited bit of extra testing.

This won't likely happen until this Saturday and will depend on the crew numbers at the shoot as to whether I can take time out to play with the second camera.


Stuart.

The Siemens chart suggests there might be room for improvement by reference to what I have observed with another Letus Extreme on a different camera type. Unfortunately I don't have the same chart to make a valid comparison.

A MINI35 will resolve the "B" block (862 lines ) on a Lemac chart on a JVC and on the Sony Z1 and gives signs on both that optically, the cameras see the "A" block as there is a distinct moire pattern visible.

The Extreme on the Sony resolves the "B" and a moire pattern on the "A" block at a comparable framing as the Mini35 and when reframed for the wider view and the Lemac chart repositoned to frame in the wider view, the apparent resolution improves.

From my own opinion and independent of the Letus designers intent, my concern relating to performance does not concern the centricity of the groundglass frame but the centricity of the projected image which falls upon it.

In easyspeak the important bit is centre of Nikon lens image falling in centre of image seen by the camcorder. The generous groundglass area on the Letus Extreme and I think the Brevis and SGPro is a bonus where sometimes some added resolution can be sought with more zoom-back, but is not an absolute given. For consistent and predictable results across a range of SLR camera lenses I think 28mm image width and no more is about as wide on the groundglass as you should want to go.

If the client wants a vignette, then I would introduce it as an effect in post. If it absolutely has to be done in-camera I would make a cardboard do-nut to shove in the back of the Letus against the achromat and trim the inside diameter of the cardboard do-but until I got it centred. My personal preference is to shoot clean footage as you can put salt in the stew but you can't take it out again.

I observe with the Z1 and PD150, the centre of image shifts with zoom-in.

The Panasonic has been anecdotally reported here at dvinfo to do this as well, which direction I do not know. How the JVC behaves, I no not know.

It is a pretty tough call to expect adaptor builders to customise to the variety of offsets of different camera types with thread filter ring attachments.

It would require a lockable adjustable offset within the ring, a dog to build, a dog for the operator to set up and a potential mongrel for off-axis errors.

The alternative is designing to permit user access to the guts of the adaptor to move prisms or mirrors about.

P+S recommend people do not climb inside their MINI35 to get at the internal adjustment for reasons of introducing contaminants but they do advise that it does exist.

Letus have been more generous with user access information in a new manual about to be published but they also recommend against operators going beyond a certain stage in roaming around inside their adaptor.

The MINI35 for the Z1 relay focus point hits sharp uncomfortably close to the infinity point. My personal preference and it seems Letus also, has been to hit sharp focus much closer to the close-end of the relay focus range.

I can't speak for Dennis's Brevis, Wayne Kinney's SGPro or Brian Valente's RedrockM2.

The P+S Technik approach has obvious advantage in that operator relay focus errors at the faraway end might be less critical than at the close end. This requires some premium design and build quality management which is what you pay for with the MINI35.

Their "connecting kits" (relay lenses included) are also camera specific and are for a fairly narrow range.

The Letus has to please a wider range with generic connecting kits based on filter mount diameter, so relay focus biased to the closer end makes good sense as there is more scope for coarse adjustment.

This also means that the practical placement of their achromat remains within the rear body of their adaptor.

If the 82mm diameter adaptor ring is intended to be specific for the JVC, then I am surprised if it has been set up to require additional macro focus on the JVC standard Fujinon lens. If is generic, then this is understandable.

I wonder if the intended direct relay option for the JVC GY-HD--- camera family, also applicable to the Sony Z7 is the main priority of their intentions for this camera type. The 82mm adaptor ring may therefore be generic for other camera types.

As to the Zacuto rails system. Please conduct one more experiment for me.

Place the camera in a safe place like over a mattress or suitable padding and no height for anything to fall.

Release the Fujinon lens/JVC lens mount locking ring. Observe any movement of the entire combination, then without assisting by pushing or shoving on the lens or adaptor or the rails, attempt to re-secure that mount ring to the closed position.

If the lockring baulks and requires pushing or shoving to enable it to close to its locked position, the Zacuto rods need to be re-aligned so that in a pre-loaded position, the lockring will release and re-secure without other assistance needed.

The MINI35 can be set up to do this. The Extreme on its Letus rails can be made to do this, even with the small pillar under the front tube. The Zacuto rails kit should be no exception.

If it cannot be set up this way, then the structure is too compliant and will introduce some bending loads on the camera/adaptor junction and camcorder case structure in normal use.

The apparent forward weight bias on the Zacuto kit is also a bit of a worry to me. There may be bounce with long lenses. If you observe Ted's setup and the Letus rail system, there are no junctions but a continous unbroken structure.

The preceding is a big and complicated message. I hope I have not thrown you into total confusion and despair. Hopefully the next few days will find a solution for you.