Here I will post pictures of my telescopes, the modifications I make to them over time, and sources of inspiration from other people that are wonderful ideas. A little place for my ATM and DIY.
(20th April, 2015)
Article: Cooling of Newtonian Opitcs - an insight
~ x - X - x ~
(29th July, 2016)
My Sketch Pad Rig
Hi all,
Thought I'd show the sketch pad rig I use and made for myself.
It came from a desperate need to have something made quickly for an upcoming dark sky trip, and that holding the sketch pad in my hands was not the way to go when up a ladder. Yet it was the very ladder that I used that proved the source of inspiration and design.
The Ladder
Taking after my mum and dad, I am not the tallest fellow in the world. And even though I built my 17.5" Karee dob to have the zenith height of the eyepiece as low as possible to the ground, I still need a single step up to reach the eyepiece at zenith.
Ok, I now need a ladder - but which one? I had to find one that satisfied a tight set of parameters:
* Stable & sure footed
* Easy of a novice to negotiate in the dark and allow them to hold onto so that they didn't first reach for the scope, especially little kids
Might seem not a broad set of criteria, but most ladders are not suitable. Either too tall, the rungs too narrow, set too steep, even too many steps or too few. Three steps would be idea. I had an old step ladder at home that satisfied the second point of my needs, and had just three, but in the dark it was too small to be stable. Then a chance visit to the local hardware store, and BINGO! There was the perfect step ladder! Three steps that were deep and wide, tall frame that allowed for easy gripping, and has a collapsible try at the top that I can use to hold the odd bit of gear. Problem solved!
The sketch pad rig
With the step ladder issue solved, a desperate need to knock up a rig to hold my sketch pad became apparent. The tall frame of the step ladder held the clue to how to design it. All I had to do was find or design a hook for the clip board I was to use to hook over the ladder's frame. Another trip to the hardware store and I found the perfect broad hook! How lucky is that!!!
Another difficulty popped up when I thought about the sketch pads I use and could use. I had A4 pads, which the clip board I had was designed for, and of course it could also hold smaller pads. But, it couldn't take a larger pad, say of A3 size. So the clip board was discarded, and a piece of perspex (Plexiglass) that was scrap from another project was the perfect size for A3 paper, and a little larger. It was also thick enough to allow the hook to be screwed into it without having the fixing screws cause interference. If I had to make this rig again, I would use plywood instead of perspex, as the perspex is very reflective and difficult to paint black. I only used perspex in this instance as it was the material I had at hand at the time as I didn't have any plywood.
The "clip" that holds the paper securely I made myself from a timber off-cut, a couple of machine screws and a couple of wingnuts. This mechanism allows me to not only accommodate any thickness of paper pad, but I can also regulate the squeezing pressure it applies so I can use either a single sheet of paper, or a really heavy and bulky A3 pad with equal easy and security - something that an off the shelf clipboard just doesn't allow.
Then the eternal problem that is the bane of amateur astronomers reared its ugly head - DEW. A heating element for the sketch pad was out of the question as the thickness alone of the sketch pads can vary, would take ages to heat the paper pad, and would just complicate the entire set up, which I wanted to keep as simple as possible. So, after some thinking about how dew forms, I came up with a simple solution. Dew forms by falling. So all I needed to do was design a shelter for the paper. And the local council elections gave me the solution for the material to use - black Coreflute® sheet. As I am right handed, the left side of the shelter could come straight down the side of the sketch rig. Overhanging element I extended out further than the edge of the rig so that I wasn't hindered by the shelter, and the overhang also provided a little more protection from dew than if I just trimmed off the Coreflute® flush with the sketch rig.
The final design allows me to hook the rig not only onto my step ladder, but also just about any chair should I need the rig to be set down lower than the ladder will allow for.
There was just one element left to allow for - lighting. That proved very easy to deal with. Firstly, the lighting should not come from the direction that one is looking from. Having the light come from where you are standing, square to the paper, you will get the glare from the reflection of the light off the paper come straight back at you, reducing contrast, washing out faint details, and hindering your precious night vision. Having the incident light come from the side, the reflection off the page is sent off to the other side of the rig, and with very little coming up into one's eyes.
At first I used a bulldog clip to clamp the red light torch I first used onto the side of the rig's shelter. Today I use a dual light gooseneck lamp with red LEDs that has its own clip that I mount into a notch I cut into the shelter. I can then move the gooseneck lights freely at will to any part and direction onto the page.
So there you have it. Inspiration, good fortune, stuff that's lying about the place, and a council election all serving to create the sketch rig that I use.
Alex.
(25th October, 2015)
My Sketch Pad Rig
Hi all,
Thought I'd show the sketch pad rig I use and made for myself.
It came from a desperate need to have something made quickly for an upcoming dark sky trip, and that holding the sketch pad in my hands was not the way to go when up a ladder. Yet it was the very ladder that I used that proved the source of inspiration and design.
The Ladder
Taking after my mum and dad, I am not the tallest fellow in the world. And even though I built my 17.5" Karee dob to have the zenith height of the eyepiece as low as possible to the ground, I still need a single step up to reach the eyepiece at zenith.
Ok, I now need a ladder - but which one? I had to find one that satisfied a tight set of parameters:
* Stable & sure footed
* Easy of a novice to negotiate in the dark and allow them to hold onto so that they didn't first reach for the scope, especially little kids
Might seem not a broad set of criteria, but most ladders are not suitable. Either too tall, the rungs too narrow, set too steep, even too many steps or too few. Three steps would be idea. I had an old step ladder at home that satisfied the second point of my needs, and had just three, but in the dark it was too small to be stable. Then a chance visit to the local hardware store, and BINGO! There was the perfect step ladder! Three steps that were deep and wide, tall frame that allowed for easy gripping, and has a collapsible try at the top that I can use to hold the odd bit of gear. Problem solved!
The sketch pad rig
With the step ladder issue solved, a desperate need to knock up a rig to hold my sketch pad became apparent. The tall frame of the step ladder held the clue to how to design it. All I had to do was find or design a hook for the clip board I was to use to hook over the ladder's frame. Another trip to the hardware store and I found the perfect broad hook! How lucky is that!!!
Another difficulty popped up when I thought about the sketch pads I use and could use. I had A4 pads, which the clip board I had was designed for, and of course it could also hold smaller pads. But, it couldn't take a larger pad, say of A3 size. So the clip board was discarded, and a piece of perspex (Plexiglass) that was scrap from another project was the perfect size for A3 paper, and a little larger. It was also thick enough to allow the hook to be screwed into it without having the fixing screws cause interference. If I had to make this rig again, I would use plywood instead of perspex, as the perspex is very reflective and difficult to paint black. I only used perspex in this instance as it was the material I had at hand at the time as I didn't have any plywood.
The "clip" that holds the paper securely I made myself from a timber off-cut, a couple of machine screws and a couple of wingnuts. This mechanism allows me to not only accommodate any thickness of paper pad, but I can also regulate the squeezing pressure it applies so I can use either a single sheet of paper, or a really heavy and bulky A3 pad with equal easy and security - something that an off the shelf clipboard just doesn't allow.
Then the eternal problem that is the bane of amateur astronomers reared its ugly head - DEW. A heating element for the sketch pad was out of the question as the thickness alone of the sketch pads can vary, would take ages to heat the paper pad, and would just complicate the entire set up, which I wanted to keep as simple as possible. So, after some thinking about how dew forms, I came up with a simple solution. Dew forms by falling. So all I needed to do was design a shelter for the paper. And the local council elections gave me the solution for the material to use - black Coreflute® sheet. As I am right handed, the left side of the shelter could come straight down the side of the sketch rig. Overhanging element I extended out further than the edge of the rig so that I wasn't hindered by the shelter, and the overhang also provided a little more protection from dew than if I just trimmed off the Coreflute® flush with the sketch rig.
The final design allows me to hook the rig not only onto my step ladder, but also just about any chair should I need the rig to be set down lower than the ladder will allow for.
There was just one element left to allow for - lighting. That proved very easy to deal with. Firstly, the lighting should not come from the direction that one is looking from. Having the light come from where you are standing, square to the paper, you will get the glare from the reflection of the light off the paper come straight back at you, reducing contrast, washing out faint details, and hindering your precious night vision. Having the incident light come from the side, the reflection off the page is sent off to the other side of the rig, and with very little coming up into one's eyes.
At first I used a bulldog clip to clamp the red light torch I first used onto the side of the rig's shelter. Today I use a dual light gooseneck lamp with red LEDs that has its own clip that I mount into a notch I cut into the shelter. I can then move the gooseneck lights freely at will to any part and direction onto the page.
So there you have it. Inspiration, good fortune, stuff that's lying about the place, and a council election all serving to create the sketch rig that I use.
Alex.
(25th October, 2015)
New use for old telescope fork mount
Hi all,
Many people who purchase a fork mounted Schmidt Cassegrain
Telescope remove the optical tube from the fork and couple it to a german
equatorial mount. However, this then
leaves a vacant set of forks.
So, what to do with a set of forks, and maybe even the
excellent electronics that may have come with it, and maybe also the equatorial
wedge and tripod all associated with the original SCT purchase?
I’ve combined this with my passion for outreach!
One thing that I love doing is sharing my love of astro in
outreach evenings. I’ve conducted
outreach nights on my own as part of larger groups. From pre-schoolers to Uni students, from
little kids to members of the third age.
I just love sharing my passion.
I am also aware that light pollution is an ever increasing
problem, and that in most instances, novice eyes combined with a washed out
city sky, most people just will not be able to view things like galaxies, or
bright nebulae. This is where an
electronic eye in the form of an astronomy video camera, can be a great asset
to have up one’s sleeve in the big smoke.
Using an astro video camera is the only form of imaging that I do, and
only as an addition to a direct visual experience.
Over the years, I have collected various telescopes. Some for specific use, and others with a
particular ATM project. One such
collection was an old set of Meade forks that once did carry an SCT. The mount was destined for the tip, and the
good mate who owned them offered it to me before it was ditched. This fork mount came with the drive and a hand
set to control the rate of the RA drive, and fortunately for me, can with some
hardware to allow for encoders to be installed onto them. And I had a couple of telescope candidates to
couple to it.
Joining the two tynes together requires careful measuring
and cutting of the joining board. Too
tight or too loose, and the bearings are forced into a binding. Once the joining board is complete, the
various OTAs can be coupled to the newly recommissioned forks!
The wedge for this Meade mount I had to make, which was easy
to do with plywood. To reduce any
possible flex from the cantilevered telescope and mount, the 15mm ply was
doubled. The plywood wedge I can also
vary its latitude position in a similar way to commercially available
wedges. I then had my kids decorate it!
I now use this fork mount now with a humble 114mm f/4.4
reflector. Surprisingly, this little
telescope is sensational with an astronomical video camera. Its short focal length allows for a very wide
true field of view, and the 114mm aperture is surprisingly powerful under light
polluted skies!
At outreach events, I double team this set up with a fork
mounted 8” SCT. Folks can then both view
through a telescope, and with some explaining, come to understand the
limitations of both an urban sky and our human eyes, and then what an
electronic ‘eye’ can offer us with even just a small aperture by comparison.
Recently I have added a set of optical encoders to the
recommissioned forks. These encoders I
have coupled to a Nexus devise from Astro Devices. The Nexus allows for a wireless connection and use my smart phone
loaded with Skysafari to navigate to objects in the sky.
This complete recommissioned fork mount, modest scope,
Nexus, astro camera & Skysafari setup goes a long way to show just what can
be accomplished with modest equipment, and a new life for equipment fist
thought to be redundant.
If you have a disused set of forks, or know of a set, I hope
this article serves to breathe new life into them.
Alex.
(20th April, 2015)
Article: Cooling of Newtonian Opitcs - an insight
Cooling of
astronomical telescope optics is a field that is misunderstood in amateur
astronomy circles. Many of the ideas
being used at first sound feasible, but they ignore the very thermal properties
of the materials that are involved. This
can result in dissatisfaction with a new instrument we have bought, or
incorrectly blaming a manufacturer for problems that are of our own making. Here I will mainly discuss the cooling of
Newtonian optics in relation to the different ways they are presented (solid
tube or open ‘truss’), and the different requirements of visual and
photographic, but only token mention of other scope designs. This revised edition of this article also
includes suggestions and corrections offered by fellow Ice In Space members. Their suggestions made me aware of the visual
bias I had unwittingly put into the first article. For this I am grateful!
Glass and
how we use it
First thing
to mention is glass. Whatever material
the substrate is, plate, borosilicate, etc, all are poor conductors of
heat. This means that they will take
time to cool down. However, as oils
ain’t oils, glass ain’t glass.
Borosilicate glass types are the preferred material for astronomical
instruments as they have a much smaller coefficient of expansion compared to
plate glass. This means that they expand
less for the same increase in temperature.
The benefit for astronomical instuments, particularly for photography,
the mirror is most dimensionally stable during the course of the night. Yet as all glass types are poor conductors of
heat, how they respond to cooling, natural or forced, needs to be understood
and work with it, not against it.
In the
original version of this article, I mentioned that the mirror doesn’t need fan
cooling. This is not incorrect, but it
was misunderstood by some people, though poorly phrased by myself. If the instrument is used for photographic it
is advantageous to quickly have the primary mirror reach equilibrium with the
ambient temperature to maximize productivity.
Fans ARE effective for this, but their application is what is most
important here. Incorrect application
can have deleterious results.
Solid
tube instrument and all photo
We know the fundamental that hot air
rises. In a long tube system, heat only
has one way to go – straight past the secondary mirror and on occasions the
focuser too. The metal tube will cool
very fast due to its large surface area, but the primary will be dissipating heat
for a longer period. When using high
magnification, these captive convection currents can become visible, and very
disruptive for photography.
Two things
conspire against us here - the length of the tube and the bulk and
consequential residual heat of the primary.
The only way to change this is to have an efficient way to create a heat
exchange. The easiest is to have the
rear of the scope as freely open as possible to have cool air be drawn in to
replace the warm. However, this is a
slow process.
Now, the
quintessential rear fan…
The other
way to create the heat exchange is to force air. This is done by the use of fans. But the way they are employed is the
key. Most mass production instruments
make use of a very open, almost skeletal, mirror cell assembly. This is fine for a long slow cool, but a poor
option for the use of fans. Most of
these instruments that have a fan attached to the cell have the fan blowing
directly onto the back of the mirror.
Two problems here:
1, the draft
of the fan is focused on one spot. This
creates a constant cold spot on the primary creating a strain within the glass
due to a forced temperature differential with the warmer extremities of the
mirror. Plate glass in particular is
more susceptible to deformation as a result, but even for borosilicate glass
this is not ideal when a better solution is possible.
2, the air
within the tube is not being exchanged as the draft from the fan is bounced
back off the mirror straight out the open cell structure – this is the path of
least resistance for the draft and it will not go around the edge of the mirror
and up the tube.
Best
practice
The best way
to force a mirror to cool, with the least way of causing a constant temperature
differential within it, is to draw the air over the largest possible surface
area.
Note:
forcing a mirror to cool does induce a temperature differential, but
this is a temporary one if the following system is employed.
In
situations of a solid tube, and for all photo applications including with an
solid tube or open, the mirror cell needs to be very open, but the rear opening
of the scope immediately behind the cell needs to be closed, and the fans that
are attached to the openings of this closed end need to blow OUT of the scope,
not into the tube and hence the back of the primary mirror. This is contrary to the initial thought of
exchanging heat out of a scope. However,
several things happen in our favour: with
air being drawn out the back of the instrument, it makes it impossible for
standing convection currents to form in the tube and the ‘boundary layer’ that
forms in front of a warm mirror is disrupted; the largest possible surface area
of the mirror is being subjected to the draft that is created instead of a
single spot; and the draft of air helps in the prevention of dew formation. This last point is very significant for
instruments that have an open tube structure.
Open tube
or truss scopes
Many of us
today make use of open tube or truss scopes.
These instruments can give us access to large and portable
instruments. But the cooling
requirements of these, particularly for visual use, are a whole less
burdensome. The first thing in favour of
open structures is there is no closed tube to allow a standing convection
current to develop – warm air vents straight out through the open structure of
the scope. The typically very open
structure of the rear cell allows for air to very easily and quickly move
around the primary mirror to evenly cool the mirror. And lastly, a slowly cooling mirror is less
problematic for visual use as we constantly switch between eyepieces, and so
alter focus, any change in the position of the focal point is a whole less an
inconvinence. The one instance when this
can be a problem is if high magnification is used from the very start of a
session and the eyepiece is not swapped – then, maybe a tiny and most likely
imperceptible change in star size might
be noticed by the most acute of eyes
as the mirror cools over a couple of hours.
Fans on the
cell of such open instruments are a futile exercise. Cold spots will be created which on very
large mirrors can create noticeable distortions in out of focus stars if these
fans are employed constantly during the course of the night. These fans will also not blow air up the tube
structure for the same reason as above – the path of least resistance is
straight back out the open cell. Any
chance of dew control from this arrangement is also lost.
Photo
application
With open
tube instruments, the primary mirror of these can be very exposed, on occasions
the mirror completely exposed. In these
situations if the primary mirror is to be force cooled, the ‘best practice’
solution described above is still the best arrangement. This will require some type of dew shield or
cuff to be placed around the primary mirror, and the back of the mirror cell
closed off in order to create the most favourable movement of air around the
primary.
Cooling of
mirrors is important for imaging to increase productivity. But it needs to be a controlled cool. If you have a closed tube scope, reflector,
refractor, SCT, Mak, etc, letting your scope cool to the ambient temperature is
advantageous as I mentioned above if you are viewing under high magnification. If you seek to employ fans, there are best
practice methods that will be most effective.
If your instrument is totally closed, like a Mak or SCT, unless the
instrument comes with factory installed fans/cooling system, there is little
that can be done to accelerate cooling. If
your scope is an open tube/truss one, a cooling period is not necessary for
visual use.
If you would
like your scope to cool prior to using it, this will take anything from 1/2
hour to a couple of hours, all depending on the temperature differential
between the ambient and that of the mirror, and the size of the mirror - small
mirrors will lose heat faster than large ones.
Dew
control
There are
three ways to prevent dew formation, heat, air flow and shelter.
Solid tube
Newt's have their primary mirror sheltered down the end of a long tube. Those
long 'light shrouds' that are often seen wrapped around open tube Newt's do the
same thing, but they introduce other complications as they get wet, and can
also trap convection currents while the primary mirror is still warm. On my scopes I use what I call a 'cuff', or
dewshield, that comes up only about half way up the open tube from the mirror
box. Since using this on my 17.5" I
have never had dew problems plague it. My 12" the same, and save for
impossible nights when even fog forms it has also not had dew problems, but
when this occurs it also coincides with the time to pack things up for the
night as seeing conditions have gone pear shaped too.
Air flow is the
way professional observatories stop dew formation on their mirrors. Vibration
from the fans is the biggest hurdle here. Once the primary is at thermal equilibrium
with the surrounds, this 'boundary layer' does not exist that can form from a
warm primary. The fans then help prevent dew formation. This method is trickiest to apply to most
Newtonians. Many big dobs made by
specialist dobs builders incorporate a battery of fans that blow across the
face of the primary mirror as their mechanism of dew control. A small fan can also be used to control dew
formation over the secondary. For both
primary and secondary mirrors, vibrations from the fan/fans needs to be
dampened.
There are
some instruments that employ fans that blow across the face of the primary, and
draw air out the rear of the primary mirror cell. These are typically high end photographic
instruments.
Heat can be
used on scopes, but it needs to be carefully employed. Secondary mirrors benefit from gentle heating
as it eliminates potential problems from fan vibration. But heating a secondary is more complicated
than just sticking a heater onto it. The
secondary mirror holder plays a vital part in this. The wrong holder and it will render any
heating efforts futile. Heating of the secondary is very effective as it is
small and the heating system can be designed to quite uniformly and gently heat
it. Heating of the primary mirror I
would suggest is not the best option, for the optical problems un-uniform
heating creates is the same as for fan cooling.
But there is
one method of dew formation that incorporates both air flow and heat – the good
old hair drier! Heating of moving air
increases the evaporative capacity, but it also needs to be applied carefully. If the hair drier is focused too much on one
spot, it will affect the optical properties of the optics. The hair drier needs to be constantly waved
over the primary mirror and surrounding structures, and from a distance, and
for no longer than is required to remove dew.
This will soften the intensity of the heat, and applies a gentle and
minor heating to the face of the mirror’s face that won’t compromise optical
performance. And to state the bleeding
obvious, if the ambient temperature is very frigid, extreme care needs to be
taken if a hair drier is to be used lest thermal shock is induced to the
corrector plate of an SCT or Mak which in extreme cases could cause the plate
to fracture. In ALL instances, the use
of a hair drier needs to be a gentle one.
12V hair driers are excellent as they have limited heating
capacity. The box of my own 12V unit is
in a very sore and sorry state I have been using it for so many years. I should look at replacing this long serving
little cardboard box.
Note that the hair drier solution only has intermittent effect as dew will form again requiring the use of the drier once again.
Note that the hair drier solution only has intermittent effect as dew will form again requiring the use of the drier once again.
~ x . X . x ~
If you look
at professional observatories, they do use fans. But looking closely at how
they are used, not one single fan is blowing onto the primary mirrors directly.
The fans are used to blow across the
face of the mirror to blow away any dew that can form on it. Also, these mirrors are not allowed to get
warm during the day. These observatories
are giant cool rooms, air conditioned to the temperature the evening is
expected to drop to, so these huge mirrors do not get warm, ever. Such massive mirrors may take all night to
reach equilibrium, if not several days.
Allowing these to get warm is something professional astronomers cannot
afford to do. In an ideal world we might
all like to be able to keep our instruments under temperature controlled
conditions. But this is not possible for
most of us. So if we do consider the
cooling aspect of our scopes, we need to do so respecting the thermal
properties of the materials being used, and the way that air does and does not
move.
It took me a
while to rationalize the misuse of fans on scopes. Particularly now that I also
build scopes, how glass behaves thermally has become more significant in my
mind in order to best design the instruments I build.
If you would like more specific information regarding your own particular requirements, please follow this link to the discussion thread of this article in the Australian amateur astronomy Ice In Space:
Article: Cooling of Newtonian Optics, Ice In Space
There you will find people with specific skills within visual and imaging who would be well placed to assist. This article is intended as a collection of the current ideas of best practice, and a starting point for understanding the principles behind the cooling of optics. It is beyond its scope to offer singular information for any one instrument. That can be addressed at the link above.
If you would like more specific information regarding your own particular requirements, please follow this link to the discussion thread of this article in the Australian amateur astronomy Ice In Space:
Article: Cooling of Newtonian Optics, Ice In Space
There you will find people with specific skills within visual and imaging who would be well placed to assist. This article is intended as a collection of the current ideas of best practice, and a starting point for understanding the principles behind the cooling of optics. It is beyond its scope to offer singular information for any one instrument. That can be addressed at the link above.
Clear skies,
sharp pencils and cool cameras,
Alexander
Massey.
~x.X.x~
(4th Dec., 2014)
SCT fine focusing - cheat's way
One problem I've encountered routinely with my lunar sketching is the problem of focusing at high magnification. It is unavoidable as I swap around eyepieces until I find what's optimal for the conditions. And it can be a real drag! To compound this, the focusing knob on my old C8 SCT is small in diameter, so even my smallest hand movements translates to an excessively large angular movement of the focusing knob.
Sure, there are after market focusing motors available, but all of these take away from the simple-to-use aspect that I want out of my equipment.
Then, the solution presented itself to me one day while playing with my son's Lego. Playing with some gear pieces, a long forgotten article on modifying a focusing knob was dragged out of the depths of my memory! Just increase the diameter of the focusing knob! Oh so simple!
I have no idea where I read that, but it would have been some astro magazine when I was a boy. But obviously it made an impression, and nearly 30 years later it came back to help me out! WOOHOO!
I had a circular plywood cut-out from another project lying about. Chance had it that its diameter easily cleared the space available between the focuser knob and the 2" visual back on my C8. The diameter of the scope's focuser knob is a shade under 22mm, so after using a 22mm forstner bit to hollow out the off-cut's center, a little strip of sandpaper between the knob and the plywood extension and I have a brand new focusing knob!
The new knob is oh so sensitive to the touch. It just needs a baby's breath to move it. And as the new knob is five times the diameter of the original, my smallest hand movements now translates to 1/5th the angular movement of the original. Focusing is now a whole lot less of a task, and less time consuming.
.JPG)
A friend suggested I make it look like a ship's wheel. Talk with another mate was around the Steampunk fashion. I took both of these and came up with a neat little decorative touch to the new knob. Nothing beats a lick of varnish too. I'm happy with the result.
.JPG)
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