Bringing back to life a Salmoiraghi 5” of 1920s


This is the little story of an unexpected project.


Just before Easter 2008, I was badly after a 160 Unitron being advertised on eBay… when, all of a sudden, my attention was taken elsewhere...

In those very days, discussing with a Gentleman about classic and ancient telescopes, he handled me a couple of papers… showing a brand almost forgotten (at least in the Astronomical domain).

A jump into the past. Wonderful instruments. Very rare indeed.

Apparently no more than a handful of these telescopes of various diameters still exist,
obviously well kept in Observatory Museums.




Oh, well, I ask if I can have a copy of the papers for my archive.

At this moment the Gentleman - almost hesitating - asks me whether I am really interested… and I would be keen… “You know - he says - something so old can be in such bad conditions”… I am not quite sure what we are talking about…

He takes me into a stockroom, where I find a tall super heavy old pier in black cast iron and two big wooden boxes in quite a bad shape. I mean BAD. Inside, to my great surprise, are stored the components of a 125mm Equatorial Refractor  (N.12 in the Catalogue page hereunder).




Oh my…!

The instrument is coming from an old dismantled observatory.

It’s a 1920s vintage.

It went rusty in most parts. And this… “will be yours, if you feel like restoring it”…!  Of course I was quoted a price but, honestly, it was a nominal one.

My ears are buzzing: I neved did something so complicated. But I cannot possibly imagine living these boxes forgotten. I feel this as a honor, a true service to History of Astronomy.

I cannot possibly say no. I shall learn.

So, yes, of course, yes: I take it.

Well, not like that, of course: I had to hire a truck so as to move the cast iron pedestal, and all the rest…!

Getting back home, I devote an area of my flat to the instrument and started a cereful analysis.


The tube is Walnut. Conical shape. Bad conditions.

State of the tube end.



Scratches on the tube.



Interior of the tube, showing a series of metal reinfocement rings.



Mmm, here I need a professional Refurbisher. Luckily I’ve got a good one.


As per the metal parts, they’re mostly rusty and jammed. Here I’ll do it myself.

Focuser and Finder block



Everything is painted. But paint is basically gone.

These images of the Weight-Driven Right-Ascension Mechanism with Speed Regulator on top can provide an idea of the general state.

Mechanism was rusty and jammed as well.









Under the paint, much to my surprise I realize that everything is brass.

Handmade, solid brass. So, I tell myself I shall go for bare brass.




Luckily, the Objective shows no scratches. Just plenty of fungi.



So, let’s do it.




While the Walnut tube is with the restaurateur, I start for days and days (weeks… months…) to carefully dismantle every single piece, getting rid of the paint, the dirt, the rust, etc.

Little by little, my working table shows the advancements…






When all the components of the OTA are ready, I move to the Weight-Driven mechanism.

A nightmare. A true nightmare.


The easiest was the Speed Regulator


A Work-of-Art in itself: everything is hand made, down to the spring.

The glass is blown (with small bubbles inside).



Then a loooong work started to open up and clean all the mechanism with acid…




It was impossible to recover the wire, which was severely damaged in two points… gotta find a replacement.




When the Walnut tube came back from the Restaurateur, I was finally able to put all the pieces together.

Not an easy task indeed, as everything is hand made and each screw wants its own hole.

For three times I failed.

The fourth attempt was the good one.

Now, after almost 90 years, the telescope is back to life !

This is a detail of the focuser side, with the finder.



Side view of the focuser and finder



The whole OTA resting on the bed.

Being 170cm long, it is difficult to picture it anywhere else, till I am not finished with the mount…




After quite a bit of Wonderfluid and Wondercloth, the lens back to life as well…


And now it’s the time of the weight-driven mechanism…


Finally all the pieces are ready.



Time to put things back together…



We’re almost there…




At last... !!!





One last piece and… 90 years later… welcome back to life…!



As I said, I still have to find a replacement for the steel wire, but that is not worrying me too much.

Btw, any hint from any reader on where to find a suitable wire would be much appreciated.




Now it’s time to work on the mount itself.

It will still take a while.

But we’re surely getting there…;-)




In the meantime, here are a few goodies:


An Helioscope in its box.

Perfectly preserved.

It came with the Telescope.


And, last but not least, the original Eyepieces box with planetary filters (not shown: there is a hidden compartment)

Just minor cleaning needed.


Using the filters it came out that the lens is heavily optimized for Mars observation.

On the blue side of the spectrum the spherical is nothing extraordinary.

On the other side, with a red filter in place, images are extremely sharp.

It was obviously built in Lowell and Schiaparelli era.




Well, as already said, I am not finished with the restoration yet. But, when I saw the OTA and weight-driven mechanism back to life, I thought it was time to start sharing the story.

Hope you enjoyed reading it !




PS: Obviously, that eBay auction went totally off my mind… so someone else is now happily looking after the 160 Unitron…!