Last year I did a review on a $100 telescope and in this video we're going to look at one
that costs half as much. And it turns out it's actually a pretty good little telescope. And if
you keep watching I'll show you how to make it even. Wetter welcome back to the Reflactor
channel. The holidays came early here. Mrs Reflactor knows that I'm a big fan of the
Dobsonian style of telescope and she found this little 3 inch Dobsonian for just $52. So
this is called the Celestron FirstScope and I've seen these go for as high as around
$70 to $75 and I've seen them sell used for about $30, so keep your eyes open and you can find one
of these cheap. I'll put an affiliate link down in the description box below. And of course Celestron
is not a sponsor... yet. So let's go ahead and open up this box and see what a 3 inch Dobsonian looks
like. Let's open the box. It is a 3 inch Dobsonian telescope... of course it's upside
down. Very satisfying sound. So okay, here it is. What it
looks like so it is a 3 inch diameter telescope and it has a focal length
of 300 mm. All right, so let's open this up. All righty we got here we got some
foam like that we got a box with something in it. We've got instructions, but we'll ignore those for now.
And before I bring that out, let's look what's in this box. This supposedly comes with
two eyepieces. There they are. Assume it's in here, we've got a cleaning cloth,
we got two eye pieces. All right so the first one is an H20 mm the H stands for Huygens. A 20
mm will give you a magnification factor of about 15 right? 300 divided by 20 is 15, so the
H stands for Huygens. The Huygens style eyepieces are one of the oldest and simplest form of
eyepieces which also means they're one of the cheapest to make. Fun fact: this eyepiece design
was actually invented a few years before Isaac Newton invented the reflector telescope. Now the
second eyepiece we have here is SR4 mm. The SR stands for Symmetric Ramsden. It's also a very
old cheap design and at 4 mm that gives you a magnification of 75. I was hoping that this
would come with at least one of the Plossl style of eyepieces. Those are kind of like the "Honda"
of eyepieces. Plossl isn't a brand, it's actually a style, and it's been worked out and it works
really really well and it's hard to make them poorly. Plossl's are reliable, they work well, and
and they are affordable... but I guess the Plossl aren't as affordable as a Huygens or Symmetric
Ramsden. Now let's get to the good part. Just reach in there and pull this guy out there it's in a
bag. Pinched in there, there's some
foam. All right look at this! This is a tiny little Dobsonian. It's so small and so adorable. I think
this might even be more adorable than the old Cometron Co-62 that I reviewed a little while
ago. Let's see, oh it's got really smooth azimuth turning and the elevation the altitude up
and down it has a little knob right here that looks like... yeah you can make it pretty tight
or as loose as you want. Here's the little thing that says don't look at the sun - we're not going
to look at the sun. It appears to have the three Teflon bearings in there, it's a nice
little azimuth bearing there. On the back there it says Celestron 76 mm, that's 3 inches roughly and the focal
length of about 300 mm. Oddly enough that's the same length as the old Cometron Co-62 as well. It's
got a little dust cap and look at that, it's a tiny little 3 inch mirror. That's pretty cool
it's a tiny little 3 inch mirror see if you can see that one thing that's one thing it didn't
come with oddly enough is a viewfinder it has the two threaded nuts here for a viewfinder attaching
like a red dot finder or something like that but it didn't come with one I guess you can just I
guess the magnification is so low that you can kind of eyeball it I don't know it does have a
rack and pinion focuser there no surprise there every introductory telescope you're going to find
has a rack and pinion let's see how loose it is though it's kind of it's kind of Wiggly I
am very curious about the colation on it I know you can't ask for much it was only $52 but let's
pull the cap out I have my colimation cap here and I'm going to point at the light and take a look
it's not too bad actually I mean it's certainly centered the mirror might be a little bit canted
but it looks like it's centered so I it can't fault them for that fun fact you can actually
buy an accessory kit for this style of telescope and it comes with a viewfinder and it comes with
a moon filter and a couple of other eyepieces which I assume are also cheap Huygens or Ramsden
than variants of eyepieces right away you can probably upgrade this by buying a $20 Plossl
eyepiece and maybe a Barlow but uh we're going to go ahead and use the eyepieces that it came
with all right we need to talk about spherical mirrors you may have heard this term before so
all reflector telescopes have a mirror at the back and it's shaped like a bowl now the bowls
come into various shapes the cheap mirrors have a spherical shape and the higher priced mirrors have
a parabola or in the three-dimensional world they call it a paraboloid shape now rather than tell
you why that's important let me just show you let's go out and look at the moon but first we
need a viewfinder of some sort now at first I thought about attaching a Telrad
to it but you know I couldn't really couldn't really figure out where to mount
the main part to it I guess I could attach it with rubber bands I might end up doing that
but if you don't have a $50 Telrad there's another trick you can use you can just take a
straw it's fairly straight through there I can already see something let me try to focus on
it oh yeah now's a great time to push the like button thanks and we're going to take take the
straw we're going to tape it here this is a long straw so it goes from the front flange to the back
flange I'm going to tape the front
on I'm going to tape the back on and then when I take it outside I'll be able to lift this tape up
and move it left and right to fine-tune it so I will need to adjust it but you know what let's go
outside let's aim it at the Moon
I've got the 20 mm eyepiece in there notice how the moon begins to stretch
whenever you move it towards the edge of the view it's actually
surprisingly sharp you can see some of the spherical aberration on there but I
don't see much in the way of chromatic aberration let's zoom in with the 4 mm
IVs it gives a pretty good image with the 4mm eyepiece
it's not quite as sharp obviously as the 20 mm now let's try an 8 mm
Plossl that actually looks pretty good uh it does run into the issue where you can
either focus on the middle of the moon or the outer edges of the Moon uh that's just part
of the spherical aberration let's see if there's a cheap way to fix this spherical
elaboration let's tell a story of two mirror cross-sections the first is spherical the second
is parabolic forgive my art skills uh this is supposed to be a circle and this is supposed
to be a parabola so here's the problem there's a common misconception that all of the light
rays coming in from a spherical mirror focus at a common point but that's actually just a
myth the reflections from a spherical mirror actually coales into this region right here
and it's more of a range of focus so it will provide an image that is either sharp in the
middle and blurry a little bit further away or it'll be blurry in the middle and sharper
a little bit farther away you can adjust it by turning the focus or Knob this is an aberration
that is caused by the spherical mirror on the other hand the higher end telescopes we use a
parabolic mirror and all of the light rays coming in do in fact focus at a common point this mirror
is a little more expensive to produce than this mirror so let's talk about this spherical mirror
these are cheaper to produce uh to counter the spherical aberration that you run into
you can take all the extra time and effort to grind this mirror into a parabolic shape as it
turns out the spherical mirrors are used quite a bit in things like Schmidt-Cassegrain and Maksutov-Cassegrain
The trick that they use though is that they pre-treat the light upstream in the case
of a Schmidt-Cassegrain they have a corrector plate that pre-treats the light and bends the
light rays coming in so that when they do hit a spherical mirror it will bounce off the secondary
mirror and out the back and produce a very sharp image and of course the Maksutov-Cassegrain has a
lenticular lens - a big thick piece of glass. It does very similar thing uh and that's how they use a
basically I guess a cheaper spherical mirror to still produce a nice image going out the back by
the way this plate up here on a Schmidt-Cassegrain is not just a flat old piece of glass it actually is
an optically designed piece of glass that will pre-treat the light coming in that's why you
can't just go down to Home Depot and buy a piece of glass to replace that if you happen to break
yours what do we do about the spherical mirror that we have on our little Dobsonian what can we
do to fix that one of the interesting things with the spherical mirror is you can actually minimize
the effect of the spherical aberration and you do that basically by only using a smaller section of
the telescope and you basically are producing a telescope that has a much longer focal ratio so
if you only use this little section of the spherical mirror it turns out that you get
Behavior that's very similar to a parabola now of course there is a limitation to this because
you're going to run into the diameter of the mirror that it's blocking now there is a way to
actually force your telescope to use less of its mirror and that is to produce a mask think of a
washer upstream that is actually going to reduce the amount of light coming in and it's going to
basically use less of that spherical mirror so that's why I have this box here I do like Cheetos
but we're going to make a mask so this is the dust cover from the little
Dob let's trace it
out put little
tabs like that and let cut it
out now after doing some research online about what diameter make the hole in the
middle it turns out that if you make it about 1.75 inches that works pretty well with
this particular telescope so I have this hole saw right there put that right in the middle B
Circle we'll cut that out
too now we'll tape this onto the front of the telescope let's go see if it improves the overall
image I can't get the whole moon in focus I can either get the middle of the moon
or the outer edges and it still has kind of a a hazy edge let's put our little mask on
here okay that's pretty
fantastic it's completely sharp and there's the haze is completely gone from the edge once again
this mask is a little bit of magic Wow I've had a chance to use this a few times now and I have to
say it's really starting to win me over it's cheap it's solid as a rock and it is truly portable it
will fit in any size car and as it turns out you can get in several different designs this
one's pretty cool it has a map of the moon on here with 10 different locations marked out and they're
listed here so right away you have things to look for while you're using this on the moon there are
of course a couple of letdowns on this the first are the eye pieces it really does ship with some
junky eye pieces you throw in a couple of plal and it would greatly enhance the experience of
using this telescope it also has these threaded nuts right here for putting a viewfinder on here
but it doesn't come with a viewfinder sure does make it a little bit harder to use than it needs
to be and of course it has the spherical mirror which we've already discussed now if you do add
the eyepieces and the Red Dot finder and you try to basically enhance the mirror then you start
to get into a higher end telescope for example the Orion Starblast 4.5 inch Dobsonian. This thing
is really cool I really like this I've been using this for quite a while it comes with a parabolic
mirror a red dot finder and some really nice eye pieces I've actually done a couple videos on this
one but of course the Orion Starblast is a $200 range and up telescope and this one's going to be
in the $50 to $70 range so who does this really appeal to well it appeals to children mainly in
fact if you have a child that has a budding interest in astronomy this would be a great
budget friendly first telescope to get them. Just be sure to provide some supervision while they're
using it so they don't try to point this at the Sun. That WILL cause permanent blindness. Now if
you want to support the channel and you do feel like ordering one of these I do have an affiliate
that Orion Starblast telescope that I showed just a bit ago, I actually have a couple of videos that
I've already made about that one. But until next time, thank you for watching and clear skies