PrimaLuceLab Sesto Senso Electric USB Focuser

primaluce lab

by Tim Cowell

Pointless Gadget?

Surely this is the height of laziness, a motor to turn the focus knob for you! Incredible, I thought as I folded my copy of that month's star magazine closed. Thinking of all manner of better things to spend my hard earned money on (food and car fuel were uppermost), the day passed. Not too many days later and with Jupiter centred and tracking well in my cam's on screen view, the battle for focus began. Every touch caused a wobble, every breath a wibble. I held my breath and stayed still.

What now?

Surely my suppressed pulse can't be affecting things? The image swam back and forth and with the best guess approach, I tapped sequence 'Run' and crept away to find that starry mag' article for another read. When my first bracket and belt focus machine arrived, it was literally strapped on and I was hooked. This was some years ago and since then I have tried a number of designs.


Crafty Affair

Let's be clear, I did not want to ever use a focus gadget because I enjoy focussing. I like the snap in the view, the spin of the knobs and the feel of the mechanism. The joy of getting the moon 'just right', back and forth, bingo! There is an art to it and a craft.

That old magazine had advised clearly what to look for and pictured a range of designs complete with belts and brackets and wheels, all very, gadgety. The one caught my eye in the adverts subsequently was the PrimaLuceLab Sesto Senso (sixth sense) design. No wheels, no belts, no brackets. No slop, no slack, no problemo!

(Not yet familiar with PrimaLuceLab? They make telescopes, good ones. They make accessories, good ones. Founded in Italy, their products are very well received globally and the Italian influence makes for a unique ownership experience, borne of form, function and flair).

If you had any doubts about quality before your unit arrived then, holding it and a cursory examination will allay any fears. The case itself is made from solid metal (this is typical of PrimaLuceLab) coated beautifully in their deep, red, corporate colour and highlighted with a white top and logo. Connections comprise 12v power socket input (a cigar lead is supplied), a small USB port (a nice cable is supplied) and a port for a thermometer (a thoughtful, useful addition).

PrimaLuceLab supply the necessary drivers and documentation on a neat little USB stick, which I really like (I use mine to keep the latest versions of a number of drivers stored for the inevitable bumps in my setup).


A Fitting End

The clean lines of the fitted device come from the compression collar clamp which is designed to fit neatly around the back housing of your telescope focuser, where it grips tightly - no brackets needed here. Inside the case of the Sesto Senso is a powerful and accurate motor. Installing the equipment for my refractor involved the following simple steps.

1. Remove the fine and coarse knobs from 'scope by undoing their recessed grub screws. This

exposes the focus shaft.

2. Now find the correct shaft connector (these are coloured tubes which are supplied in the kit) and

fix it by its grub screws to the 'scope shaft.

3. Carefully slide the unit onto the telescope, so that the shaft connector tube slips onto the motor

shaft of the Sesto Senso. Using the access slot underneath the 'Senso, tighten the shaft connector

grub screws and lightly tighten the main body clamp.

Hex head keys are supplied, which is incredibly handy and thoughtful. For my particular telescope I needed the extension collar, which comes with its own packet of slightly longer shaft connectors.

There were no dramas at all in fitting, which was one of my primary reasons for choosing this item, having read some forum reviews.


Making Connections

Following the proper order, I quickly installed the drivers and special software for calibrating the device. With the 12v power hooked up, I plugged in the USB cable and noted the COM Port Number assigned, by checking it in my Device Manager. The Sesto Senso software is quick and easy to use. Click to connect your unit and choose between SCT or refractor type. Calibration asks for the focus position to be set at the mid point and then both fully in and out positions are found and the calibration steps are stored. This is quickly done. I chose not to use the fully in and fully out positions of the true mechanical travel. I'm a 'what if' type of person so having 10mm from 'in' and 15mm from fully out have not been a problem with my cameras etc.

You can use the software provided to control things or use your image capture software via ASCOM. I use Sequence Generator Pro and things have worked so well that it is hard to imagine wanting or needing another solution.

Night Worker

With rough focus found in the usual manner (daytime on a distant object) tweaking the beast was

simplicity itself using both the supplied software and SGPro. I kept its power setting to the preset

Heavy and Slow because the motor appears to be incredibly strong. The Light and Fast preset

option was slightly ferocious, so I will stay at the slow end as it is more than enough.

To determine the accuracy and begin to see what, if any, differences there were in focus between

my filters, I popped a good quality diffraction spike mask on the telescope and checked my monitor

for the results.

Firstly, it all works marvellously. A slick and classy way to automate and improve focus accuracy. I was a 'happy bunny' that first night and after as much use as I can give it, I remain perfectly satisfied. With more usage and a little tinkering with the filter offsets and step values I settled into a routine of using the auto focus and periodically checking against the spike mask during strategic pauses in my imaging sequences. All satisfactory for my purposes.

I don't know of a hand controller on a wire for 'Senso, however since it is PC controlled I use a remote desktop app on my phone and hence have the best hand controller possible; big, bright and should I drop it I can borrow my wife's.

This is such an easy creature to get along with that I often forget about it. It is no 'squeaky wheel' requiring nagging attention. It is a faithful and trusted companion in the night. The gently glowing power light blinking away like a friendly lighthouse. I have bought a second unit for my other imaging refractor. The price is very keen, the justification being based on the great performance of my first Sesto.

I am pleased to report that all duties have been performed with flying colours. Sitting somewhere between 'not quite essential' but 'certainly not a gadget' my sixth sense tells me that when I next need / want a focuser the friendly UK importer will get another online order.