Hi this is Graham from Jenham's Astro in this video we're going to have a quick look at this
telescope the Celestron C90 Astro this one's about 45 years old and we're going to look
through some of its features and specifications if you think that might be interesting you haven't
already subscribed to my Channel please hit the Subscribe button now okay so what
is the Celestron c90 Astro well it's a small Maksutov telescope with a 90 millimeter mirror
a thousand millimetre focal length f/11 and it was supplied by Celestron from the late 1970s onwards
and similar to the C5 astro that you might see on my channel it is supplied with a single fork mount
ready to go onto a wedge and a tripod and it is really a mini Observatory all in one
small package I want to say small I really do mean small this thing is smaller than my coffee machine
it weighs just under four kilos you can carry it around like it's a dumbbell you'd probably
need two of these but it's a really compact telescope very solid and doesn't feel like it's
45 years old probably the kind of thing that made the Saturn V out of.
so if we have a look at its some of its features as I say it is an f11 Maksutov
it comes with a quirky focusing mechanism that you would have seen in my other videos on the
old c90s so it's a helical focuser which love it or hate it but it works okay on this Mount because
it's it's solid and you don't really transmit too much vibration through when you're focusing
the telescope so that's a bit of an unusual feature comes with a 5 by 24 finder scope
which let's be honest is not really big enough to be of any real use so I'll probably swap it out
for for a red dot finder when I'm actually trying to use this scope a little bit more
so yeah single fork mount
slow motions on both axis axes declination and right ascension
and it is designed to be driven so if you look underneath you can see there is a motor here
there you go and this one is 110 volt US supply so you plug in you plug in the cable
here I got one of those
like so and it drives the synchronous motor this in this case a single motor and then
basically you can track in right accension if you've got the scope on a tripod and a wedge
so what else came in the Box well everything came in this box which
I really like it's super compact so inside aside from the telescope itself
um came with an instruction manual which is definitely from the 1970s and some interesting
equipment described in there but yeah came complete with that came with the AC cable
and it came with a box of accessories which we're going to have to have a bit of a look
at because some unusual features here so coming around the back this coat the scope is supplied
with the old size 0.965 inch um accessories so you need an adapter if you want to run with
modern 1.25 inch eyepieces but for now we'll forget about that it comes with what you need
imagine we're in the 1970s if that's possible so it comes with a diagonal which is a prism diagonal
and you'll notice straight away that it doesn't have any obvious uh thumb screw to attach uh to
tighten up an eyepiece in but we'll just we'll carry on for now put it in the right way it's
going to work better so it has a thumb screw here to tighten against the the diagonal there we go
and then it comes with one eyepiece so it is a Kellner in this case an 18 millimeter focal length
it just slots in like that and it's held there with a little bit of friction it's
a little bit spring-loaded the diagonal tube against the eyepiece so that's it
and nothing no screw to tighten up nice and simple a bit unusual though
so you're ready to go with the 18 millimeter eyepiece and that's the
lowest power that you're going to be able to achieve with with the standard kit
it also comes with this device which kind of looks like a Barlow but it's more than that it is in
fact a combination of a Barlow and an extender now I had to look this up to figure out how I would
use it in this telescope and there are a couple of pages to explain what you do but essentially
you try and get this right now you unscrew the two and a half times Barlow
element I hope you can see that there and then you actually screw that on to
the diagonal which has a thread inside the tube and then that can operate like so so in this mode
you go from I think it illustrates in the manual we go from 55 times magnifications with just the
eyepiece up to 140 times so okay bit unusual but we haven't come to this bit yet so the tele
extender is the next step so in the manual it explains I'm having to refer to it here because
it's not at all obvious it explains you can put the extender in this configuration and then
put the eyepiece in like this so like this you can get to 200 times so I haven't really tried it
out at high power yet I've certainly tried it out with the standard eyepiece and it certainly works
pretty well I've yet to see how this this level of magnification how it coats with that but we'll see
but a really unusual sort of setup not the kind of thing we really see too much of these days
okay so other features so I mentioned the um the fact that it's got a helical focuser but
I think probably certainly myself and maybe other people likely to get most use out of this by
deforking it sorry probably sacrilegious to some but it's very easy to remove the optical tube
from the mount and you can see actually if I take out the I take the eyepieces out a minute
so we don't drop those on the floor but if you look underneath the tube you can see that there
is this pad it's a bit loose so I'll tighten that up once you've removed it from from the
fork you can screw this into a standard tripod thread so it's easy to mount on a photo tripod
easily adapted if you want to put a dovetail bar on if you wanted to mount it onto an astronomical
telescope Mount rather like an equatorial Mount and I'll probably do that I'll probably put
this on some of my lightweight equatorial mounts because as I say it's four kilos with the with the
um the mount and probably only a couple of kilos for the optical tube
so I hope it's been useful it's just a brief introduction to one of these you don't see
them very often um perhaps one of the interesting things I haven't mentioned so far is that there
is a registry of these items as there is for older C5s and C8s you can come across that on
Cloudy Nights and it tells you how you can figure out how old it is and essentially on the motor
you can just about figure out the date that the motor was manufactured in this
case it's some point in 1977 I believe there also is a serial number that can be found
if you look inside the the corrective plate so the combination of those two things dates
your telescope to some degree or other so this one I figure is around about 1977.
so it is slightly older than the C5 Astro that you've seen probably on another video
I need to use the scope a bit more to tell you if it's actually any good I've looked at the moon
really nice views haven't tried it at higher power so I'll have to reserve judgment on how good it is
at this point and maybe make a future video about that certainly when I figured out how to adapt
the visual back to use larger eyepieces so I hope it's been useful,
if you haven't subscribed to this Channel please hit the button and look out for
future videos on this telescope and some more modern kit as well okay thanks for watching