Testing out my system after 6 years

[alpal]

Hi All,
I have just completed my indoor testing of my 10" f4 telescope system
which hadn’t been fired up since January 2017.
I’m very pleased as I was never sure that everything would still work.
I finished the maintenance so far –

mostly outside cleaning and then I assembled it all.
All electrical contacts on the UPS were cleaned.

All batteries were replaced with new batteries.
The UPS needed 2 new lead acid gel batteries 18A/Hrs each.

I made a collage of some of the pictures of it.
see here:
https://i.ibb.co/tL3vHn3/telescope-s...ng-28-1-23.jpg

Everything is still working:
Main camera QHY-9M using EZYCap software.
Filter wheel – 5 position for LRGB Ha.
Guide camera - Lodestar using PHD2 guiding software,
Electric focuser with hand controller,
Mount with its SynScan hand controller.
Power supply - like a UPS - with its 3 off 12 Volt outputs,
Charger,
Both DC to AC inverters.
The laptop works and controls both cameras and filter wheel and mount with its software.
The Telrad is working with a new battery and needs to be mounted.


The only thing I found was the main mirror and secondary mirror could do with a clean.
That’s a big job but I have plenty of time and it will be cloudy for a while.
I look forward to testing it under the stars.


cheers
Allan

[alpal]

I'm getting ready to pull out the main mirror and secondary mirror and clean them.
I'll take some pictures as I go and post them here.


Talking of the main mirror:

Back in 2015 TS -Teleskop Service in Germany

- were offering certificates for their ONTC mirrors.
I'm not sure if they do now?
Here is my certificate from 2015 for my 10" f4 ONTC mirror completed by the famous Wolfgang Rohr.
You can see that the Strehl ratio is 0.922.
Peak to valley 1/6.8 waves.
RMS 1/22.1 waves.

here:

https://i.ibb.co/G5TSG9S/10-inch-f4-...t-complete.jpg
using Google translate on the German text it says:

TS Mirror – TSHS250f4
D=258mm
Mirrored surface=254mm
SN=A_TSHS250f4- 04/09/2015
Slight overcorrection (about 1/6 lambda) in the middle.
However, this area is covered by the secondary mirror, so that the mirror is significantly better in practical operation than 1/6.8 wave.


cheers
Allan

[alpal]

I am still checking out the Newt.


I haven't cleaned the mirrors yet.
I'm investigating the collimation and anything that might affect it.
See the pics attached.
I put my laser into the focuser and and centered the spot inside
the paper reinforcement at the center of the main mirror
by adjusting the 3 screws on the spider -
I then adjusted the 3 collimation screws on the primary mirror cell
but I noticed that the spot changes position slightly if I move the telescope from a horizontal to a vertical position.
This is not helped by the 50 mm extensions I made - years ago -
in order to achieve focus when the coma corrector
was just starting to enter the main tube -
the ideal position for it.
It was either make 3 extensions or cut the valuable carbon fiber tube
to fit the mirror cell end piece over the end of the tube.
The cantilever effect of that extra 50mm makes the lateral movement
of the primary mirror worse than stock standard.
I notice that the Newt. designs I've seen all have a lateral movement
problem as there is nothing to stop that from happening -
the collimation screws work at right angles to the sideways/lateral movement so don't help much in that regard.


I found the collimation would not hold steady from other things too:
At first I traced it to a loose grub screw in the focuser - see pic.
Tightening that made a big difference.
As per the other pics it's very difficult to know that the true center
of the focuser laser aiming is correct even though I have a
brass compression ring on the 2" to 1.25" convertor - see pic.
which should in theory hold everything perfectly in alignment.
So at the moment I'm thinking about what to do as I don't want
to be like a dog chasing its tail over problems that don't exist.
When I last used the telescope it worked very well with nice round stars
right out to all 4 corners of the KAF8300 sensor.
Any thoughts would be appreciated?


cheers
Allan

[alpal]

Hi Guys,
I've got a simple idea that could apply to any Newt. mirror cell to prevent sideways lateral movement
so that collimation is maintained from the vertical to the horizontal position of the telescope tube.

The laser spot from the focuser should not move when the tube is moved.
2 off L brackets are used for each each section.
You could have 3 or even 4 L bracket systems each consisting of 2 brackets connected by a spring.
Each one is separated by a strong spring.
There is a wide hole in the bottom base plate L bracket so
that the system won't bind with different tilts of the mirror.
Now there is a strong spring resisting lateral movement which works only in compression -
but the 3 collimation knobs can be adjusted as per normal.
I did a quick drawing.
What do you all think?

cheers
Allan

[alpal]

Talking of lateral primary mirror movement.
Dan from stargazers lounge designed and built a mirror cell
device that prevents lateral movement here:
https://stargazerslounge.com/topic/3...m-mirror-cell/


I attach a pic of it here:

[alpal]

I often think of amateur astronomers who have won many awards including APODs
and have large libraries of beautiful pictures without using high end scopes and spending megabucks.
In this case Carlos Taylor is using only
a SkyWatcher Quattro-10S (250/1000) Newtonian reflector
which retails for under 1,000 Euros:
https://teleskop-austria.com/SWN2501...nian-reflector

and has a 2" focuser.
he just won another APOD here:
https://apod.nasa.gov/apod/ap230119.html

and he has an astrobin library of amazing pictures here:
https://www.astrobin.com/users/CAPastrophotography/

[alpal]

Putting it into perspective:

if you want to use a full frame camera as per many imagers then it starts to get expensive -
you need a 3" focuser and corrector which would cost much more than Carlos Taylor's entire Newt. -
in fact 3 times the price or more.
Then a full frame CMOS camera would cost 4 times the price of his Newt.

The primary mirror moving around is a bugbear of just about every Newt.
What mirror cell can you buy that has any design in it that stops lateral movement?
People put stronger collimation springs in which helps but only masks the problem.
This should have been sorted out 40 years ago by the all those so called engineers
who designed the mirror cells.
Amateurs have had to do DIY modifications to make things work properly.
Consumer law says that a product sold should be fit for the purpose to which it is intended.
No one should have to re-collimate their Newt. every time they use it.
They should hold collimation for months or even years and certainly not change
collimation when the OTA is moved from vertical to horizontal.

[rmuhlack (Richard)]

A pertinent thread for me, as I have also just this week fired up astro gear (that had been out in the observatory shed) after a similar period of inactivity (about six years for me too). The PC that had been left out there is struggling, but the mount and scope are okay, and I actually managed to collect some respectable shots (some easy lunar to get my feet wet).

[alpal]

Originally Posted by rmuhlack

A pertinent thread for me, as I have also just this week fired up astro gear (that had been out in the observatory shed) after a similar period of inactivity (about six years for me too). The PC that had been left out there is struggling, but the mount and scope are okay, and I actually managed to collect some respectable shots (some easy lunar to get my feet wet).

Nice going Richard,
the pictures look great -
it must be a good feeling to finally fire everything up.
Are you still able to take long exposures while guiding with PHD?
Will that be your next step?

I kept all my stuff indoors in mostly locked cupboards.

cheers
Allan

[rmuhlack (Richard)]

long exposures while guiding with PHD is the plan for the other scope (VC200L) and mount (NEQ6). However before I get too carried away i'm going to have to take everything out of the astro sheds to give them a good clean. SO MANY BUGS !!

[alpal]

Originally Posted by rmuhlack

long exposures while guiding with PHD is the plan for the other scope (VC200L) and mount (NEQ6). However before I get too carried away i'm going to have to take everything out of the astro sheds to give them a good clean. SO MANY BUGS !!

Yes - it's worth doing.


In the meantime I bought some hardware from Bunnings
to help me work out how to install 3 lateral loading springs for my mirror cell.
I think I know how to do it. see pic

[alpal]

I finally made the first of 3 lateral axis spring devices for my telescope.
The first picture shows the device placed under the primary mirror but
not bolted on with the wing nuts yet.
The next 3 pictures give different views of the mechanism.
I had to make many parts - including the L brackets with 2 holes -
one hole is a slot type to allow tension adjustment of the spring
when all 3 are finally fitted.
The wooden block is made out of very hard wood.
I had to use calipers to draw a radius on some paper and transfer that to the rounded end
to match the inside radius of the carbon fiber tube.
It fits the tube perfectly and took ages to get the curve right.

A flat blade Speedbor was used to make an 18mm hole for the spring to fit.
A piece of copper tube and some cloth tape was used to make
a bushing for the end of the bolt closest to the L bracket.
A brass bush would have been nicer but only a machine shop
could make that and it's not critical.
A spring bucket would be nice inside the wooden end piece but
once again I don't have a lathe to make one and
I don't think it's critical either.

Now I have to make the other 2 and then drill 3 holes in the mirror cell to mount them.
I'm hoping this will be the answer for millions of people out there who have no lateral control
of the movement of their primary telescope mirror
which causes their collimation to change when the telescope is in different positions.



cheers
Allan

[Startrek (Martin)]

Allan,
Great post and thread
Very ingenious design on the primary too
I’m a Newt man through and through since the start
Gee I’m glad I image at f5 not f4
One observation I made was that my carbon fibre newt holds collimation better than the metal tube newts ( obviously little or no thermal expansion along the tube from end to end ) Although that’s at f5 , f4 may be a different proposition

Cheers
Martin

PS: I’ve ordered another Klaus Helmerich Carbon fibre tube for my 8” f5 GSO metal tube newt , so will be retrofitting in March

[alpal]

Thanks Martin,
I like imaging at f4 - it's much faster.
I want to get a good image in less than one night and maybe
even get 2 good images in one night.
Yes - carbon fibre Newts hold collimation better than the metal tube Newts
and they also hold focus without changing for hours on end -
in fact they can hold focus all night.
Good luck with the new CF tube.

I just finished my 2nd wooden block as per the pics.
I'm doing it slowly at my own pace.

One thing that worries me about my design is that it's so
simple why didn't someone else do it before?
is there a problem with it? - e.g -
will it affect the focus or the guiding?
A 2 axis closed loop system as per PHD2 guiding may not work
as well with unknown spring constants causing a change in the dynamic damping -
if anyone knows - please chime in?
In any case I'll soon find out - in fact it's a good scientific experiment.



cheers
Allan

[alpal]

Latest news:

I finished all 3 assemblies for the anti-lateral movement springs.
In order to treat the wood I soaked it in raw Linseed oil -
then wiped clean -
it's already bone dry after one day - might need another coat?
I changed the washer setup as well.
It's ready to be installed.

I'm thinking about whether I should install the mirror fan as well ? -
I was told that it makes little difference for a 10" mirror.

cheers
Allan

[strongmanmike (Michael)]

Ok, I'm confused....the problem is not normally the primary mirror holder that moves or "flops", as the scope tracks across the sky but rather the actual primary mirror itself..?

What am I missing here..?

Mike

[alpal]

Originally Posted by strongmanmike

Ok, I'm confused....the problem is not normally the primary mirror holder that moves or "flops", as the scope tracks across the sky but rather the actual primary mirror itself..?

What am I missing here..?

Mike

Hi Mike,
not the mirror itself but the mirror cell or mirror holder.
Look at most telescope mirror cells -
or at least the ones I've seen.
They have 3 collimation adjustment screws underneath the mirror cell.
What keeps the mirror cell and mirror in place when you move
the OTA from horizontal to vertical?
The 3 screws don't have tight threads - there will be some movement sideways.
That will affect the collimation when the OTA is at different positions.



cheers
Allan

[alpal]

Update:
I was wondering about my laser and if it was suitable for precise collimation?
I found out that it wasn't orthogonal.

After some internet research I discovered that the laser is easily tested
by clamping it in a vice and aiming it at a graph on the wall.
When first tested the error was over 8cm at my target 4.3 meters away.
Luckily the laser has adjustment Allen head grub screws.
They were sealed with silicone so I removed that and preceded to adjust it.
The least error I could get after 1 hour of tinkering was a 4.2 cm or 42 mm. see pics.

My testing involved rotating and re-tightening the clamping screw
in the 2" to 1.25" adapter- - which has a compression ring.
The fact that I could rotate the laser a full 360 degrees back to zero degrees and be on the same spot gives me confidence that my testing method is sound.
A 42 mm error at 4.3 meters away equals
inverse Tan of 42/4300 = 0.56 degrees.
My 10" f4 telescope has a FL of 1016mm
so the error in collimation will be 42/4300 x 1016 = 9.9mm
when projecting the laser spot on to the paper reinforcement circle.
That to me seems hopeless to use as a collimating too?
see pics below.
can anyone please comment?


cheers
Allan

[big-blue]

Hi Allan
I have had consistent results from rotating the laser in a v-block such as a piece of angle iron or aluminium.
A V-block minimises play in any radial direction so that you can re-set axial accuracy while rotating the laser. I reckon I get to within couple of mm of dead centre with careful adjustment, via target at a few meters as you have done.
The eyepiece holder such as you are using might still have residual radial L-R slop under the single thumbscrew. Just the act of clamping could shift the laser.
When I find a good eyepiece holder in my various bits, I set it aside to use for collimation in my Newt. Once I know the laser itself is collimated, I rotate this 'best' EP holder with laser fitted, to check its own wobble. Good luck.!
& btw, my own preferred method for collimation is via Cheshire eyepiece.

[alpal]

Originally Posted by big-blue

Hi Allan
have had consistent results from rotating the laser in a v-block such as a piece of angle iron or aluminium.
A V-block minimises play in any radial direction so that you can re-set axial accuracy while rotating the laser. I reckon with care I get to within couple of mm of dead centre with careful adjustment, via target at a few meters as you have done.
The eyepiece holder such as you are using might still have residual radial L-R slop under the single thumbscrew.
When I find a good eyepiece holder in my various bits, I set it aside to use for collimation in my Newt. Once I know the laser itself is collimated, I rotate this 'best' EP holder with laser fitted, to check its own wobble. Good luck.!
& btw, my own preferred method for collimation is via Cheshire eyepiece.

Thanks - I'll try that.
The eyepiece holder does have a compression ring which in theory should hold the laser or an eyepiece in exactly an orthogonal position.
It does return to zero precisely after a 360 degrees turn and locking.



cheers
Allan