Letus rattle

[James Sidney]

I've just taken shipment of my Letus. Works great except when I point my camera downward, which causes the letus to make a rattling sound. Seems like something might be loose, but I don't really want to look under the hood unless I need to. Anyone else experience this?

James

[Bob Hart]

It may be that the Letus has taken a hit for the team during transport. Although the Letus may have been well padded, the glass elements are a heavy mass and if a package is airmailed onto the conveyor by the baggage handlers, bounces over the edge to ground, no padding can always protect against glass elements moving and coming loose or getting chipped.

The journey in large aircraft is not always gentle. Items towards the rear of a large aircraft can be subject to frequent lateral movements of about a 3Hz period for about a second after the fin passes through turbulence and torques the airframe.

The best move is perhaps to notify the vendor immediately. There may be a warranty or transport insurance applicable, however there will be time limits within which you need to lay claim. Your vendor will likely advise the best course to take which may be returning the appliance for checking and repair.

If however you would rather trouble shoot for yourself and risk voiding any warranties or insurances you could perhaps perform the following checks.


Do some initial survey and preparation and then seven tests for us to contemplate here. Be aware that these may compound an existing transport damage and void your warranty :-


Survey :


Check all machine screws are secure and no joints are loose.

With the Letus assembled to the camera and the front lens removed, aim towards a light source, not too bright as to damage the camera, pull back on the zoom until you can just see all edges of the groundglass frame, pull relay focus very slowly from the groundglass, closer through the condensor element.

Look for any very fine powdery deposit on the glass surfaces of the condenser near the edges. Whilst looking through the viewfinder, roll the camera and Letus through more than 120 degrees from left through to right and check for any movement of the condenser element. It will not roll, but may rock just a very small amount if its clamps have become loosened. Look also for small cracks across a corner.

While doing this also look for sudden slight jumps in the image, fragments moving within and sense for any things moving inside.

With the camera removed and looking through the adaptor from behind through the achromat, check the edges of the prism path. Are there any crystalline bright areas, rainbow patches or small blind spots intruding in from the darker straight blind edges which border the clear path?

With the front lens mount removed from the Letus, check the glass panel in back of the lens mount hole from the front to see if it is squarely in its fitment at the edge.

With the camera removed from the rear of the Letus, check the achromat is firmly screwed into the rear of the Letus. If it is secure, then look particularly around the edges of the glass.

Do not remove the achromat rim from the rear. There is nothing to be gained from this as the next surface in is one face of the rear prism beyond which you cannot poke or probe.

There may be some tack bonding marks around the very edge of the achromat glass where it rests on an inner shoulder face. These are normal.

Are there some crystalline looking rough areas more than about one millimetre or one sixteenth of an inch in area reaching across the glass from the edge? If there are, with a cotton tip or cotton wool swab to prevent marking the glass, gently drag on the glass surface from one side to the other. It should not move in the rim.

If all glasses are not observably loose, move to preparation.


Preparation.

Cross two strips of strong masking tape or gaffer tape across the rear of the achromat but not touching the glass. This is to catch the glass if it happens to fall free. No other glass elements can actually fall from the appliance if they have been damaged.


1. Point the Letus front-down with the motor running. Is the rattle still happening?

2. Hold the lens firm in the mount or remove the lens from the Letus. Point it to the ground again with the motor running. Is the rattle still happening?

3. Use a cotton tip or cotton swab not bare fingers to avoid making marks and gently touch the glass panel inside behind the lens mount while the rattle is happening. - Does the rattle cease?

3. Point the Letus directly skyward with the lens fitted back on. Is the rattle still happening?

4. Hold the lens firm in its mount or take the lens off while the Letus is operating and pointed directly skyward. Is the rattle still happening?

5. If the rattle has stopped, check the front glass and the glass elements in the rear achromat to see if they have moved.

6. With the front of the Letus pointed directly toward the ground, with one finger knuckle, rap gently but sharply, the front tube of the Letus from sideways, working your way around the tube. Is there a single rattle in reply?

7. With the front of the Letus pointed directly toward the ground, with one finger knuckle, rap gently but sharply, the flip enclosure from the side, working your way around the casework. Is there a single rattle in reply?

8. With the motor running and the Letus facing level to the horizon, gently roll the Letus through a full 360 degress clockwise, then anticlockwise. Is there a rattle at any point through the rotation?


Hints:

A light loud clatter when the Letus is in a normal position or is rotated whilst aimed at the horizon, suggests edge of groundglass carrier to inner face of tube contact, a rare event.

A softer light rattle which goes away when not facing directly downward, suggests a loose front glass element, which will only be loose when it is square-on and will tighten when it tilts back in its hole and binds when the Letus is brought back to a level position.

A heavier almost silent rattle, which can be felt more than heard may be a loosened prism which is a heavy glass piece within the flip enclosure.

Any of these symptoms indicate damage has occurred in transit or someone dropped the appliance, which brings back warranty and transport insurance considerations.

[James Sidney]

Thank you for the lengthy reply Bob. Honestly I'm very intimidated about opening up or inspecting the inside of the Letus. All I can tell you is that the screws are all tight, and the rattling occurs when I tilt the camera over on its side or point it down around 70 degrees or more. I'll be calling Zacuto tomorrow.

One more thing: Seems to me that the focus is way off when I'm using my 28-70 lens at the wide setting. Elements on the same focal plane are not sharp on one side of the picture frame. Even if I'm pointing at a flat wall, one side is soft. I can focus and correct for that side and bring it sharp, but no way this should be happening with a wide angle lens. Any thoughts about that?

Thanks again,

James

[Bob Hart]

From what you describe, the groundglass panel is not square-on to the focal plane. this in company with the noises you describe suggests one of the three pillars has come forward in its socket or even come out of it and the groundglass panel, no longer restrained on one corner, is hanging forward when the appliance is tilted forward.

This would move the whole panel sideways far enough for wall contact to occur, hence the rattle. Odds are that if you could observe the image as you tilt the Letus forward, there would be changes in the focus of the groundglass image apparent one side.

The fix is fairly easy if no parts are actually damaged or missing but only if you have the confidence to take it on, an understanding of the optical theory and mechanics plus fine dextural skills.

It is not unknown, but not common for pillars to come free.

There may be two possible causes.

The Zacuto kit installs the Letus in an inverted position on doglegged rods. If there is a coloured thumbscrew fastened centrally beneath the front tube, holding the front tube down onto a pillar and bridgepiece across a rod pair, it is likely the front tube has been dismounted, rotated through 180 degrees and refastened. It may be possible that a pillar has been disturbed during this modification.

In the alternative, the package your Letus came in may have copped a solid clout from front-on or near to, possibly an overshoot and hard landing after being tossed onto a conveyer and tumbling off to the floor. The Letus and its attached camera are intended to do a great many things but stunt work is not one of them.

Partial dismantlement to check the groundglass is fairly easy but do not do this unless you are confident Letus AND Zacuto agree to honour their warranties if there is actually a component failure discovered by your inspection.

To inspect the groundglass, find a clean dust-free location.

Unscrew the four setscrews, which are found as two pairs in the cylindrical housing near its junction with the flip enclosure ( the big angular shaped box part behind the front cylindrical section. ) There may already be a small allen key (bristol wrench) in the Letus/Zacuto kit which fits, the same one for securing the lens mounts.

Draw the cylindrical shaped housing gently forward. It is a snug but not tight fit on a short shoulder. Take care that it comes off directly forward and the section it comes off from does not kick as it slips free as there is a chance the groundglass carrier may be damaged or dislodged even more.

Once that section has been drawn forward, you will observe the groundglass carrier, an attached small silvery coloured motor and some green wires. That tiny motor and its eccentric weight are the very beating heart of the Letus groundglass motion system.

You will be able to see if one of the pillars is no longer attached to the rear housing or if some other moving part is damaged. Re-installing a detached pillar is another matter, again easy with practice but requiring some fine dextural skills and vernier calipers or precision steel rule to set the groundglass panel square-on to the focal plane.

If you end up successfuly repairing it yourself, when re-assembling the tube housing back onto the shoulder, take care to observe that the position of the mounting hole for the rods and pillar support faces the same way it came off.

My suggestions may not reflect factory or reseller systems and methods so please consult with them first.