Hi this is Graham from Jenham's Astro today I'd like to review this the ZWO
atmospheric dispersion corrector now the idea of an atmospheric dispersion
corrector is that it can improve your view of planets that are close to the
horizon so this could be when you're visually observing them or when you're
imaging them and what it does is it tries to take away an effect that's
introduced when the planets are low down and the different wavelengths of light
are dispersed or separated as they travel through the thick lower
atmosphere. So inside this device there are a couple of prisms and you can
adjust them as we'll see shortly and the idea is that it can remove the effects
that you see either in the eyepiece or on an image of that image of that
dispersion of light, so in a way it's similar to having a telescope that has
false colour and this device is aiming to reduce or remove the false colour in the
UK is for sale for around 115 pounds
okay so what's in the box well not much as it turns out just the device itself
don't expect any instructions so we'll see how we get on. First thing to notice
is that it's a device that will fit into a one and a quarter inch draw tube on
one side and then on the other side you will be able to connect a camera or a
diagonal or eyepiece. You can see that it's got a spirit level here which is
basically because you need to have this device fitted such that it's horizontal
against the horizon when you're adjusting it so that's something to bear
in mind when you've found your target in your telescope and other than
that what can you see well it looks like we've paid quite a bit of money for not
very much because you can see straight through it but it turns out that there
are actually two prisms inside the unit and the correction that it applies is by
rotating these prisms relative to each other
and it does that by means of these two levers. So you have two levers that can
be moved independently of each other like so so you can move them so they're
pointing completely different directions or you can bring them back to be in a
datum position like that and on the side of the body of the unit you can see some
graduations to allow you to perhaps to reproduce a given position or to make
sure that the two levers are adjusted symmetrically so they should always be
up and down by the same amount. So now we're going to connect it well I'm gonna
use Sky max 127 and then 2 times Barlow and an ASI 120MC camera so these are
standard parts of the setup I use for imaging, and when we use the ADC we
put the barlow into the visual back it doesn't go fully in
but that's okay it's not elegant but it reaches focus then we're going to
attach the ADC so that goes in here behind the barlow and we tighten it up
and then finally we're gonna put the camera into the ADC like so and that is
the basic setup we're gonna use we're gonna take a few videos of Venus and
experiment with the settings of the ADC so before we do that the only other
thing to note really is if you have a slightly different setup if you don't
need to use a barlow and you have like this scope okay so your visual back has
a T2-thread then the zwo body comes apart and you can see a
thread which allows you to mate the ADC directly onto the back like so so that's
can give you quite a nice secure connection if you don't need to put
anything between the visual back and the ADC but in our case we're gonna I'm
gonna use a two x Barlow to get a larger image scale. So this is the first capture
so initially the levers on the ADC a horizontal or they're at the zero
position so they are adjacent to the datum screw little screw you can see
behind the levers and also you can see that the ADC itself is orientate
horizontally with the horizon so there's a little bubble level on the top which
allows you to set set the horizontal axis on the right you can see the image
this is a five hundred frame capture that's on a loop and I think it's pretty
clear that the fringing you can see the dispersion of the color is quite evident
so on the upper side as we see it there's quite a lot of red and yellow
and on the lower side there's distinct blue tint so clearly in this case the
zero position on the ADC is not removing the
dispersion so this time the levers are separated up to the first division
either side of the datum so I'm calling this nought point 5 position but each
lever is adjacent to the first of the marks on the side of the ADC body so
looking at the difference well the fringing has pretty well disappeared I'd
say compared to the to the the first capture so this looks to be
approximately the right position to get rid of the fringing so we'll see we'll
process the image later and see whether indeed the color has been removed so now
the levers are separated to be adjacent to the first bold mark on each side of
the body i'm calling this position one and looking at the image perhaps there's
a little bit of orange they'll be a color on the left-hand side of the
planetary disc as we see it here it comes and goes
I think you can just about perceive a little bit of fringing but no
significant color I'd say on either the the north or the south of the planet so
now the levers are both separated by one and a half of the major divisions either
side of the datum and it's think you can see from the image the video that there
is now some evident yellow orange fringing on the lower side of the planet
and some blue on the top so the fringing that we saw on the datum position of
a zero is swapped over so we're obviously applying too much correction
here and to find the optimum position we'd probably have to go back just to it
to a smaller offset of the levers so finally last capture this one the levers
are adjacent to the second major bold marker on the each side of the ADC body
so I'm calling this position 2 it's pretty clear from the image that
the fringing has got worse as you would expect and now we can see quite a lot of
orange-yellow on the lower side and quite a lot of blue on the top okay.
So here are the results so what I've done is I've taken the AVI file put it
through the PIPP tool in order to centralize the image of Venus cos my
tracking wasn't very good and then I've taken each of those files and process
them in Registax in exactly the same way so done a basic alignment and
stack and then we've taken the best 100 frames out of the 500 frames in the file
and performed a very basic wavelet adjustment so there's no color
adjustment whatsoever in Registax so moving from the left to the right I
think we can see that when the ADC is applying no correction we've got some
fringing and then somewhere around the nought point five to the one position
the the color dispersion is removed so clearly in this example that's roughly
where we want to put the levers and they're moving over to the right as
we've separated the levers further the fringing has come back in an opposite
sense to where it started with the zero correction. I think the ADCs done the
job , Venus is a difficult target its always low in the sky, very bright
and in my case at least I am pushed for time as the planet tends to
set behind one of my neighbor's houses so everything's a little bit rushed and
it was quite straightforward to use the ADC both photographically and also
visually quite intuitive once you get used to the fact that you've got to keep
the ADC level using the spirit level and to keep the to adjust the levers
symmetrically as it were so pretty happy with that. I'll leave it to you to
compare the results versus using the color adjustment tool in Registax but
for me it's done the job and I look forward to using the ADC on the other
planets particularly Jupiter and Saturn so I hope it's been useful thanks for
watching bye for now