hi this is Graham from Jenham's Astro people often ask me what telescope they
should buy if you want to get into Astro photography
well I normally say to them is they should buy a small refractor telescope
something maybe 70 millimeters in size for the aperture maybe 70 or 80
millimeters and they should try to buy one this so-called apochromatic or semi
apochromatic and that means one where the main objective lens is made of glass that
brings all the wavelengths of light to focus around the same point now these
telescopes there's a wide range that's available lots of different
brands in the UK you're probably talking about price of 300 pounds upwards but
the sky's the limit basically you can you can spend an awful lot of money so I
suggest that they buy a telescope like that a small low dispersion glass
refractor and they put that on to a lightweight mount. I got to thinking
whether there was an alternative is it possible to learn the basics of astro
photography using an even cheaper optical tube than one of those and maybe
using one that is an achromatic lens. achromatic telescopes these are ones
which don't have this clever glass so they normally get over the problems of
that can cause in terms of seeing false color within the image or so-called
chromatic aberration they get over this by having long focal lengths so these
things look like long pipes really and they're the traditional old-fashioned
view of telescopes but it is possible to take another route so this video does
just that and it looks at a small achromatic refractor so this is the short
tube 80 which is a model that's been available branded under quite a few
different names for a long time it's currently branded for example as the
star travel 80 so in this video we're gonna have a look at this refractor
which on the face of it isn't very promising as a piece of equipment to use
for astrophotography and we're gonna see if we can get some decent images
okay so the short tube 80 so basically if you buy one of these new just the
tube assembly and the fittings that it comes with in the UK it's around 100
pounds they've been around for a long time so you can find these telescopes
used maybe from around 60 pounds on an auction site and it's also careful when
you check out a scope like that buy from a reputable seller then fingers crossed
they're fairly robust scopes they should be okay so what do we know it's as the
name suggests has a lens that is 80 millimeters in diameter and it has a
focal length of 400 millimeters that's to say there's 400 millimeters between
the lens and the point where the light comes into focus so you can see it's
about the actual tube when the light bends around here and it's 90 degrees
then this it's a foot and a little bit long it's got a focal ratio of f/5 that
means that the focal length that 400 millimeters divided up by the
aperture and you get five so it's an f5 or a fast 80 millimeter refractor it
weighs about one point eight kilos and if you compare that to a weight or a
digital SLR the sort of thing we're going to be using in this video that
weighs about nought point seven kilos so the whole set up ready to sit on a mount
is gonna be around two and a half kilos so it's quite light weight even though
it's as mechanically quite a sound item lots of metal quite chunky but still
only two and a half kilos all in with the camera so these telescopes are
generally supplied with tube rings which are these items here which clamp around
the outside of the tube and they'll often have some kind of bar here
dovetail bar which is used to mount the scope onto telescope mount this
particular one has a red dot finder although you sometimes
see optical finders and they come they can be removed and changed out comes
with a standard bracket here to fit a different finder the focuser is pretty
basic it is a rack and pinion focuser here you can see it single speed which
is to say it doesn't have a feature that you get on more sophisticated telescopes
where you can have a fine one-tenth scale focusing, focusing being very key
in astrophotography but it's a basic focuser and it has quite a good feel
it's quite solid doesn't feel like it wants to to move around very much and it
also quite importantly for astrophotography has a screw here that
allows you to tension the focuser so if you've got a camera hanging off this
then you can tighten it all down and nothing really moves so what would you
need to do if you had a mount and you had a camera what would you do to get
started with this scope well I'm not going to go into the details of the
techniques for actually taking the photo all really gonna cover is how you attach
the camera okay so if you've got your digital SLR then the first thing you'll
need is one of these which is a t-ring which you buy one of these it has the
bayonet mount for your particular camera type on one side and then there's a
standard thread size on the other so you get one of those this is a canon camera
and you click it on like that now it seems that that standard thread is
conveniently already provided for you on the back of the ST80 so there's a
thread here which actually is the same as the thread on the inside of this
t-ring so I could actually screw the camera directly onto the focuser and
that would appear to give a really firm mounting arrangement the problem is that
often in order to actually focus a camera so imagine you're focusing as we
say at infinity so if focusing on an object a very long
way away a star for example on the moon in order to actually bring this
arrangement of camera and telescope into focus you need to put need to put some
more distance between the sensor in the camera and the back of the telescope you
can't actually find that focus point even if you have the focuser fully
extended like that so if you imagine you could screw it in like that it won't
quite reach focus. To bring the image into focus in fact
you need to separate them by another couple of centimeters so if you buy one
of these used you've got to make sure you look out for whether it has one of
these things called an extension tube if not you can buy one for a few pounds and
it simply slots into the focuser like so and tighten it down and allows you then
to attach the camera where you want it to go so now you need to put another one
point two five inch adapter that screws into your is your t-ring like that and then
finally you can attach that into the extension tube at the back of the
telescope so that seems a bit of a pain but it's quite common with small
refractors like this basically they're designed so that normally they bring the
light into focus when you have an eyepiece and a diagonal so imagine
you're looking at a star visually you're observing something up high in the sky
so you have one of these 90-degree diagonals to bend the light and make it
more comfortable basically if this is the arrangement when the star comes into
focus if you imagine taking away all that extra focal length of light
bouncing around that diagonal and you go to put your camera sensor at the same
place that your eye was and you can see that in fact you need the camera sensor
to be here and not he so just basically be aware you're
probably going to need an extension tube quite common these sorts of telescopes
even more expensive ones. so we're ready to go we're going to put this
arrangement the camera and the telescope onto an equatorial mount one that has a
drive to move it in the right ascension axis and we're going to just see what
kind of quality of image we can get so I'm going to choose a range of targets
and take a look at the results and basically the objective is to see is
this telescope good enough so that you can get your skills building up on
astrophotography is it the weak link or would you be the weak link if you come
in to astrophotography and you choose to take the route of using a very basic
very simple optical tube like this so let's give it a go and see how well it
performs.
so the first target looked at is the planet Venus this is taken with
a two times Barlow using a digital SLR now the reason you can see me over
on the side of the frame is because well there's lots of space this object
doesn't fill the frame nowhere near so this is Venus this is what you'll see if
you video it with a digital SLR or if you take a still image with that setup
of telescope and Barlow and if we zoom in
you get a rainbow so basically Venus is a very bright target at the moment when
I when I took this shot this high in the sky so we're not looking through a lot
of atmosphere still it's so bright the ST80's short focal ratio has resulted in
us getting all this chromatic aberration so we're really seeing this false color
separation in the wavelengths of light and really it isn't very good so I'd say
not only is a digital SLR not really suited to photograph the planets with a
scope of this sort of focal length but the scope itself isn't really suitable
for photographing a bright planet so moving on to the moon again with a 2 x
Barlow I think this frame is probably got just
about the right exposure so that you can see some detail in the craters and if we
zoom in then the edge of the moon there's a tiny bit of color evident but
it's not what I call significant not distracting if we were to increase the
exposure a little bit and then we have another look we're starting to see some
color fringing here we're starting to see a little bit of violet red and then
if we go further again so this time we try and catch a bit of earthshine longer
exposure higher gain on the camera now whilst we can see the other side of the
of the moon there's quite a nice image in that respect if we zoom in we've got
quite a lot of color purple fringing evident at the edge of the moon so it's
not done too badly I'd say in these conditions the the sky wasn't very dark
so that you get more effect noticeable when the moon is high in the sky and a
different phase and a fully dark sky that still you start to see a bit of
chromatic aberration but certainly the ST80 can give you pretty nice views of
the moon but they're not perfect moving on to deep sky objects this is
the Perseus double cluster so this image is taken from ten 30-second frames now
30 seconds is a very evil short duration that you should be able to get from a
lightweight equatorial mount if you've done a half-decent polar alignment I
think you can see that this shows the ST80 is capable of achieving nice small
well-defined star images across the frame of the digital SLR and it's also
rendering some nice color in the stars a
different type of object now this is Messier 3 globular cluster slightly
more exposure this time reasonably well defines a very small object so this is a
crop of the overall frame but I think you can see this object gets a bit
overlooked in place of m13 some other globulars nearby but I think it's
produced a good image. this is Messier 57 the ring nebula now when I took this
shot this stack of frames the ring that we was really low in the sky it was just
rising in the east so it's quite a challenge to get an
image of this so I've used lots of short frames a faster film speed or camera
speed something more ambitious this is the flaming star nebula in Auriga so this
shows that you can record nice nebulosity with a bit of practice quite
a lot of exposure time to capture this object and a little work in
post-processing
and then very famous pair of galaxies Messier 81 and 82 in Ursa Major again
quite a challenge objects high in the sky which is good
quite a lot of exposure time more exposure on galaxies gives you a better
image that's true in any telescope whether it be an ST80 or a very
expensive refractor or reflector
okay so conclusions would I recommend you have a go astrophotography using
something like this star travel 80 or an equivalent refractor telescope
well I think the answer has to be yes if you can pick one of these up but not
very much and you already have the rest of the equipment that is to say maybe
have an equatorial mount that you've got with a different telescope and you've
already got a digital SLR then this is a good way this sort of telescope is a
good way to get in to astrophotography but you put your toe into it if you like
and see I get on you can definitely get credible images with this scope the only
things that really falls down on are the objects perhaps where that you'd expect
where the focal ratio and achromatic lens are its weak points so if you try
to look at Venus as we've seen it's not going to give you a good result you're
gonna get a lot of fringing it's not gonna be very pleasant you're
not gonna see a white planet you're gonna see a planet with purple haze on
one side and red or another color on the other side it's built more looking like
a rainbow so if you avoid very bright objects like that and moons okay
although you might detect that sort of fringing around the edge of the moon
otherwise for deep sky objects so looking at nebulae clusters galaxies
even when you get bit more experienced then this short tube 80 can produce
some really good results so I'd say if you get an opportunity to pick one of
these up maybe you've got a reflector telescope or something at the moment
that you don't really know how to use and it's a bit unwieldy this is an
option to see whether you're gonna like astro photography and you're not really
committing a large amount of money. so short-tube 80 definitely better
than its price suggests I suggest you give it a give it a try and get some
good results okay I hope it's been useful thanks for watching and please
subscribe to Jenham's Astro youtube channel if you'd like to see more videos
like this bye for now.