30.06.2020 PH-20 Preventing telescope rotation on the camera plate.

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One, major problem I have found so far is the telescope [and attached camera] rotating around the fixing screw on the camera plate. I have tightened the [drop ring] thumbscrew as hard as finger tight will allow. Still the telescope objective springs half an inch from side to side. The camera even further due to the much greater "leverage."

The Kowa telescope foot and narrow ring may have some flexibility. Though I think the movement is mostly around the fixing screw. Probably due to the flexing of the rubber pads on the Sirui camera plate.

I am using the longer PH-180 plate for maximum freedom to slide the plate through the head for system balance. Ideally I need some means of restricting plate rotation. A small hole and a slot are provided in the Kowa's foot. Though the large diameter of the thumbscrew means these holes are largely inaccessible. The very shortness of the Kowa foot is another negative factor.

Manfrotto do an anti-twist clamping plate based on an L-shaped casting. The downside is the very small size relative to the very long mechanical system of telescope and camera. I can't just start drilling holes in the impeccable Kowa telescope body to fix something to the tube. So any restraint has to be fixed to the camera plate.

A curved 'crutch' to stop the tail end of the telescope body from moving sideways might work. The problem then is the stay-on bag getting in the way. A taller crutch could locate on the tubular body section at the tail end of the telescope. A right angle profile, in aluminium, is bolted to the rear end of the camera plate. Then a vertical crutch [plate with half round cut-out] is bolted to the angle piece.

Since this restraining 'prop' is fixed to the plate it will slide with the plate during balancing operations. A plastic plate would pass unnoticed in this position. I don't want to use aluminium for the upright plate. It would permanently mark the Kowa body black over time.

An hour later I had a prototype and it worked amazingly well! From half an inch of rubbery wobble, from side to side, to barely detectable movement.

Just a short length of scrap aluminium angle and an off-cut of kitchen cutting board. It needed a bit of inward bias on the angle to pull the crutch tightly into the tail end of the telescope. I have heavier sections of angle profile to make a much smarter and beefier job. That can come later if it proves to be worthwhile. There may be a flaw in the design somewhere which I haven't discovered yet.

I was delighted to see that I had colour matched the grey plastic to the Kowa "uniform." Quite by accident. It was that, or bright red! The scruffy bit of thin angle is hideous and must go!

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30.06.20 Sirui PH-20 Gimbal Head.

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As explained earlier I was very disattisfied with the Manfrotto 500 head for digiscoping. Only when absolutely level could it be considered neutral in balance. Though even that did not allow for balancing the telescope and camera system as a whole. Any deviation from level applied top heavy forces around the low level, altitude pivot. Causing the telescope to nose dive or the camera to sink. 

The further the angle [away from level] the greater the moment [mass x distance] around the pivot. The 500 head comes with a modest [built-in] reaction to out-of-balance forces. Which proved, in practice, to be incapable of limiting droop of the digiscoping system unless the axes were locked up hard. Or the telescope and camera were slid repeatedly and ever further through the head. An impossibility with the silly little camera plate provided. 

Which mean that trying to control the long and heavy, telescope and camera [see-saw] was a lost cause. I always had to be fighting the built-in droop. Which meant locked axes and an inability to smoothly follow any subject. At the high image magnifications involved this meant it was hopeless trying to capture a video.

Enter the geometric answer to my balancing nightmares: The Sirui H-20 Gimbal Head. 

The gimbal head can achieve a completely neutral balance of the digiscoping system in all planes once properly adjusted: It ensures the centre of mass [CofG] of the system is arranged at the centre point of the bearings.

First you balance the telescope and camera as a whole on the "swing." [See-saw style] By sliding the camera plate through the quick release clamp a point will be found where neither end of the telescope/camera system wants to sink. This vital step is best carried out with the vertical slide Q/R plate clamp at its lowest point on the vertical slide. Once balance is achieved you must tighten the clamp to fix the camera plate. Do not be tempted to alter it again or you will confuse the vertical balance operation. 

Once longitudinal balance is achieved, the whole optical system must be lifted gently to achieve vertical neutrality. This is done by gently loosening the vertical slide clamp while supporting the optical system.

I found it easiest to put my hand under the vertical slide plate to support it while my fist was wrapped around the curved arm. Small increments of vertical movement were then easier to achieve than trying to bodily lift the camera and telescope system directly.

If the telescope and camera are set too low then they will act just like a pendulum. Regardless of the starting point. They will try to reach the middle, or lowest point of the swing, and stay there. 

Lift the whole system too high and they become a Manfrotto 500 series head. Increasingly unstable when tilted away from perfectly level!

Vertical neutrality is easily tested by allowing the camera or telescope to point downwards in turn. The camera or telescope 'nose' should remain unmoving when either is pointed downwards. If they do want to sink then lower the optical system slightly.

A point will be found on the vertical adjustment scale where the whole system stays perfectly still once the axis knobs are released.  NO variation of this desirable state is permissible if you want to maximise enjoyment of the gimbal head. Panning and tilting to follow a subject then becomes almost effortless. Gimbal users refer to the camera and lens/telescope system becoming weightless.

Slacking off the axis clamp knobs completely should not only be possible but the ideal, default setting. Giving the telescope/camera unit a gentle shove at each end of the swing should show NO tendency to continue. Just as the system should not try to reach the middle of the swing either. It took me only a couple of minutes to achieve perfect balance neutrality from a standing start.

The PH-20 is silky smooth in movement in all directions. It stays perfectly still in any position. Just as it should be. I like the simplicity and understated, good looks. The scales are handy for remembering previous settings if you dismantle the optical system for transport.

The altitude clamping knob worked well, braking is progressive and locked the axis solidly when needed.

However, the horizontal panning axis brake/lock is a total disaster! The knob seems to tighten something into the teeth of a rather eccentric, finely toothed, rubber gearwheel! Making locking, from completely free, a sudden and extremely rough affair. Where is the graduated friction control expected of an expensive camera head? This is a Sirui gimbal! Not an Amazon knock-off at 1/3 the price!

If the knob is not fully tightened then the axis can still rock back and forth freely but over a small angle. Which is pretty weird! When most users would surely want a smooth braking effect on the axis. Followed by a gradually stiffer axis until full lock up is achieved.

How else would one pan to follow a subject smoothly? How can you frame a landscape if it cogs between impossibly large angles on a long lens or telescope? Is my gimbal factory defective?

Trying to unscrew the hex socket screw just resulted in the head unscrewing from the tripod. The underside has a metal socket for the tripod screw. This uses tiny pins on a proprietary pin wrench. I cannot imagine this is the route to examining the hidden components. I thought I might try to fix the problem rather than immediately returning it to the dealer for a replacement.

It seems I am not alone in disliking the roughness of the panning lock. The tilt friction is finely adjustable. Just as it should be. I am still hoping the panning will "break in" with a little exercise. The small hand knob needs serious torque to fully lock the axis now. 

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