Bob Hart

Stuart.


With any of the adaptors, relaying via the camcorder's own lens, you have to zoom in a fair way, some more than others, in the region of 32mm to 54mm for 1/3" sensors.

With the JVC standard zoom lenses I have played around with when modifying my own AGUS35 to fit, the filter thread is contained in a plastic housing which the lens hood attaches to.

The lens focus movement is free to move inside this housing. The housing can be flexed enough to put your image centre off.

I observe that the Zacuto rails system on some illustrated kits has a step or dogleg in the structure. The system for the JVC may not have this.

If there is a step or dogleg in your kit, this means that there are four points of fixture in the combined structure where off-axis angular or torsional deviations from optical centre can be introduced, six if you include the Letus and camera holdfasts.

Therefore angular loadings on the lens hood filter mount on front of the Fujinon could deviate the optical centre axis of the Letus relative to the Fujinon lens optical centre axis.

It takes very little deviation at the long end of the zoom-in you have to use, to move the Letus screen image frame across the camera image as viewed.

There might be variation between individual Letus units but variations introduced in the combined assembly might more likely account for the centering deviations you are observing across different individual units you have attached.

As for having to use macro focus, attaching my home-build appliance I found the standard Fujinon presented a serious challenge to my efforts. The filter mount was too far forward for best position of the Century achromat I used and I was forced to move it to the lens itself.

My imagining is that you if want to avoid macro use, you may need to dismount the inbuilt Letus achromat from the Letus body and attach the achromat directly to the front of the Fujinon focus barrel as close as you can get it.

You would need to remount the Letus body as close to the front of the Fujinon lens as you could with a custom shorter attachment adaptor ring you would have to get made in a machine shop.

You would need to make a custom ring to mount the now free achromatic inside the moving front of the Fujinon lens itself.

The new Letus attachment adaptor ring might likely need to have the allen screws replaced with short grub screws in radial holes within the 82mm filter thread itself as there would likely be only enough allowable front-to-back thickness to permit a threaded shoulder and not enough extra for a plain shoulder for the normal screws.

Because the optical axial alignment of the Letus to the camera is maintained by the threaded adaptor pieces, you will most likely have even more problems with centering if you follow my hack without making a new machined adaptor ring.

This hack would probably eliminate your need to use macro which I found to be unsatisfactory for both focus and edge distortion on my own adaptor.

Please do not attempt my hack unless you have good engineering skills.

This comment is also speculative theory so please do not take it at all seriously. I have made a few mistakes recently and the engineering for the Zacuto system you are using may be perfectly fine.

Perhaps you could post an image of your adaptor including a close-up of the LEtUS to front of Fujinon attachement to assist or correct any of the number of assumptions I am making which could be wildly incorrect.

Finally if you are achieving good edge-to-edge sharpness and no other optical defects when using the macro function of your Fujinon lens, leave best alone and concentrate on getting the alignments of the combined assembly correct.