Hi this is Graham from Jenham's Astro today we're taking a look at
another antique telescope this one made by the Clarkson company in London around
1890 it's a three inch eye achromatic and we're going to take a look at some of
its features I managed to pick it up for sixty pounds in an online auction just
for this tube assembly and I think when you pick it up it's three and a half
kilos of brass it seems like a pretty good deal now firstly back to the maker
Alexander Clarkson bought an existing optical manufacturing company back in
the 1870s. Later on he went into business with a Robert
Broadhurst and after a falling-out between two Broadhurst when his own way
and started trading at Broadhurst Clarkson and Co from 1908, so we know
that this telescope predates that certainly I'd say it's 1890s to 1900
thereabouts but the interesting thing is that it's a Clarkson scope and not a
Broadhurst Clarkson. There are far fewer of these Clarkson scopes around compared
to the BC scopes probably affecting the manufacturing volumes of the time so
next time we're gonna have a look at is the optical layout of the scope
so the scope came with one of these it's the eyepiece believe it or not it's
a terrestrial eyepiece and so why is it so long well it's quite a lot more
behind the scenes than initially meets the eye
so if we take the end of tube firstly we find that we have just a cover and then
inside we have a cartridge eyepiece which you can see I hope one of the
lenses at this end and the eyepiece end that we see is there so the whole
thing's about 2 inches long and then at the other end of the tube so this is the
end that's closer to the objective lens there's another threaded assembly inside
the tube like so so again we've got another arrangement of lenses and the
combination of all this put together flips the image right way up for daytime
use and it's probably the equivalent of Porro prism and a conventional eyepiece
but back in the day when these scopes were produced there were dedicated
terrestrial eyepieces like this one terrestrial tubes as they were called and
they were separate astronomical pieces which were more conventional I
suppose to the modern eye like this so taking a look at the focuser we can
see that we've got a focusing knob on the side of the tube which is acting to
move with an internal rack and pinion mechanism it's moving folks a tube this
one moved by I'd say about only six centimeters as is common of these old
scopes and indeed feature you seen on scopes up until the 60s and 70s
you also have a secondary mechanism for achieving focus in the
form of a push-pull draw tube here so you have to do a bit of adjustment
initially with the push-pull and then fine adjustment like so the mechanism
itself is secured inside the brass tube with three screws around the outside
here so we'll take those off and have a look inside
now if we first remove the focusing knob from the side of the tube and then those
three screws then were able to pull out the focusing mechanism and the draw
tubes like so and this reveals the the rack that is screwed onto the side of
the focusing tube and you can see quite easily how the rack and the pinion
operate against each other to focus the telescope so other points of interest if
we have a look inside the tube we can see I hope
let inside at the end of the tube there is a baffle and there's a slot there's a
slot cut rather crudely into that baffle to allow the focuser rack to move in and
out and then finally on the scope something that's worth taking a look at
is the objective lens, as always the most important part of any telescope I
came to look at this lens to see how I could remove it and started off by
turning side-to-side is thinking it was threaded but actually it turns out that
it's not the entire objective cell is just pushed into the end of the brass
tube and it's held in place with friction so there you go
there is objective lens so this is a typical achromat of the day 76
millimeters no obvious makers marks on the outside which I was hoping to see
but it doesn't really matter no obvious coating but I guess we'll wait and see
when I've uses scope with more during the day it performs pretty well so there
you go a push-fit objective lens cell so that's it,
certainly one for a summers day go buy an old scope and take it to bits. a brass
tube with a couple of baffles in a bit of black paint a nice sliding push fit
objective lens assembly rack-and-pinion focuser focusing knob and a terrestrial
eyepiece tube that's it it's been a Clarkson 3 inch refractor we've been
looking at today hope it's been interesting thanks for watching