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  #61  
Old 05-07-2018, 08:54 PM
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After some teething issues which were causing astigmatism and pinched optics I now feel confident enough to commission the scope into one of my observatories. With the dew shield on the scope presents as being much longer. Now to get some clear sky to focus and check final collimation, then on to V curves and on to the first imaging run.

Characteristically there is a major storm warning here in South Australia now. It should be over by early next week. Sunny skies are forecast for early in the week.
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  #62  
Old 05-07-2018, 09:23 PM
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Gawd, that is a big dewshield - Telstra's gone and put mobile antennae and other gizmos on it!
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  #63  
Old 06-07-2018, 06:10 PM
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Nice find on the pinched optics.

That tower shot is very sharp so that bodes well.

Looking forward to your first light.

Greg.
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  #64  
Old 18-07-2018, 08:41 AM
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Ok, its been a few weeks since my last update. I have been slowly getting through the commissioning. Some observations below.
  • The secondary position was way out. I have had to move it a considerable distance toward the primary. I think so far I have moved it about 20mm and I am still not convinced that I have it in the correct position. The size of the secondary is enormous at 110mm across the minor axis and that can be quite deceiving in an observatory with dark walls. I am now using a white piece of cardboard to help with positioning.
  • There was astigmatism present from the secondary glue. I have reglued that into position and this has alleviated the astigmatism.
  • The primary without side support moves, just a tiny amount, which affects collimation. When the primary arrived it was taped and glued to the mirror cell. This was causing astigmatism and pinched optics. I have now once again taped and glued the primary with small dobs of glue and tape to prevent the primary from moving during slews. Their idea is sound, just the execution was a bit off. I suspect that the glue was applied during hot periods in England and this caused the silicone to off gas and cure very quickly and pinch the optics.
  • The collimation is still in need of fine tuning. I plan on doing that tonight with a visit to the site if the weather holds. A fast scope like this needs star test collimation to get it 100% correct.
  • The secondary assembly hold star shapes quite well. I don't see the changes in star shapes I was seeing in the GSO. That would no doubt be a combination of the secondary assembly and the focuser assembly.
  • I'll be giving a full review of this scope once I have it working and imaging.

See images below for first light. As you can see there is still an element of miscollimation present and a bit of a way to go yet. Perhaps even some tilt present, but I won't know that until I have the collimation nailed down. Detail appears to be sound overall.
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  #65  
Old 18-07-2018, 10:41 AM
Russj (Russ)
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Hello Paul, I've been reading this thread with interest, sounds like ur working thru the problems on the new scope and its starting to come together for you.

Could you answer a newbie reflector owner question? what are the indicators on miscollimation in your photos, I cant see a problem with my newbie unpracticed eye. Nice image by the way.
Regards russ
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  #66  
Old 18-07-2018, 03:58 PM
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Hi Paul,
looks like it's nearly there.
The top left corner looks the worst.
Have you considered CCDInspector ?

http://www.ccdware.com/products/ccdinspector/

I hope you can get it perfect.


cheers
Allan
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  #67  
Old 18-07-2018, 06:27 PM
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Don't you love having to rebuild a scope you paid big bucks for. Wow, if this were a new car there would be hell to pay.

Luckily you are patient.

It does look a tad soft in the centre and the left hand side stars look fatter than the right hand stars.

I have a question though. With miscollimation you are looking for stars anywhere in the field that are eggy (not from tracking) as opposed to tilt which would be one side or one or more corners?

Greg.
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  #68  
Old 18-07-2018, 07:14 PM
ericwbenson (Eric)
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Quote:
Originally Posted by Russj View Post
Hello Paul, I've been reading this thread with interest, sounds like ur working thru the problems on the new scope and its starting to come together for you.

Could you answer a newbie reflector owner question? what are the indicators on miscollimation in your photos, I cant see a problem with my newbie unpracticed eye. Nice image by the way.
Regards russ
Hi Russ,

Miscollimation causes aberrations (other than spherical) to appear. Usually coma is the first and worst, but astigmatism can also be generated.

A simple way to think about it: the 'corrected' field is only a finite size, collimation shifts it around, when it is perfectly centered you see no aberrations, or the same aberration in each corner, depending on the size of the sensor relative to the 'corrected' field. Symmetry is the goal.

Image tilt will only induce defocus (inwards in one corner and outwards in the opposite). Defocus means the stars stay round but get bigger. NOT the same as coma or astig which makes the stars non-round. So when you hear someone blaming their eggy stars on image tilt it usually is not the case (but can be, read on...)

In reality separating the two factors (aberrations and tilt defocus) is really hard unless you have very good seeing to be able to examine the shape of the non-round stars. What can really be confounding is a little bit of inherent astigmatism in the optics (from mounting or built-in), which is not detectable in focus, but is revealed by slightly going out of focus. So now is that astig in the corners from image tilt or field curvature or collimation?!?

It takes practice and patience to iterate the setup, which is what Paul is doing now...

and then throw in a camera rotator and it becomes a really tough nut to crack!



HTH,

EB
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  #69  
Old 18-07-2018, 09:18 PM
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Joshua Bunn (Joshua)
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All the best Paul with ironing out technical issues. What was the reason to move the secondary forward?


Nice write up Eric. As I'm sure you are aware... one way to find out if it's tilt or colimation is to rotate the camera relative to the scope. If the star shapes, whatever they be, follow the chip (stay in the same place) then you have tilt. If they change place from rotating the camera, then it's likely you have an optical issue. The next issue to be aware of is, is tilt being introduced when rotating the camera .


Josh.
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  #70  
Old 19-07-2018, 12:36 PM
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Thanks guys for the contributions. Individual response below with more after that.


Quote:
Originally Posted by Russj View Post
Hello Paul, I've been reading this thread with interest, sounds like ur working thru the problems on the new scope and its starting to come together for you.

Could you answer a newbie reflector owner question? what are the indicators on miscollimation in your photos, I cant see a problem with my newbie unpracticed eye. Nice image by the way.
Regards russ
Russ the star shapes on the left corners and the top right indicate collimation issues but I also had out of focus images which confirmed this to me. The position of the secondary becomes increasingly important the fast the f ratio of the Newtonian.

Quote:
Originally Posted by alpal View Post
Hi Paul,
looks like it's nearly there.
The top left corner looks the worst.
Have you considered CCDInspector ?

http://www.ccdware.com/products/ccdinspector/

I hope you can get it perfect.


cheers
Allan
Hi Allan, I have been a long time user of CCDInspector. It gives good general analysis which helps to resolve these types of issues. Getting to the site and doing the tweaking has been generally possible during the day at present. Last night I was there but could not complete the final tweaks, which I hope can be done next week.


Quote:
Originally Posted by gregbradley View Post
Don't you love having to rebuild a scope you paid big bucks for. Wow, if this were a new car there would be hell to pay.

Luckily you are patient.

It does look a tad soft in the centre and the left hand side stars look fatter than the right hand stars.

I have a question though. With miscollimation you are looking for stars anywhere in the field that are eggy (not from tracking) as opposed to tilt which would be one side or one or more corners?

Greg.
Adjusting a folded optical design is part of the situation I suppose but I never expected to remove silicone and have to actually move the secondary into the correct position.

The left side has collimation error and perhaps some tilt or more probably error from the corrector making corrections to the collimation error.

The softness is the collimation error too. I expect it will be quite sharp once properly adjusted.

Quote:
Originally Posted by ericwbenson View Post
Hi Russ,

Miscollimation causes aberrations (other than spherical) to appear. Usually coma is the first and worst, but astigmatism can also be generated.

A simple way to think about it: the 'corrected' field is only a finite size, collimation shifts it around, when it is perfectly centered you see no aberrations, or the same aberration in each corner, depending on the size of the sensor relative to the 'corrected' field. Symmetry is the goal.

Image tilt will only induce defocus (inwards in one corner and outwards in the opposite). Defocus means the stars stay round but get bigger. NOT the same as coma or astig which makes the stars non-round. So when you hear someone blaming their eggy stars on image tilt it usually is not the case (but can be, read on...)

In reality separating the two factors (aberrations and tilt defocus) is really hard unless you have very good seeing to be able to examine the shape of the non-round stars. What can really be confounding is a little bit of inherent astigmatism in the optics (from mounting or built-in), which is not detectable in focus, but is revealed by slightly going out of focus. So now is that astig in the corners from image tilt or field curvature or collimation?!?

It takes practice and patience to iterate the setup, which is what Paul is doing now...

and then throw in a camera rotator and it becomes a really tough nut to crack!



HTH,

EB
Perfectly put Eric. Fast optics make this task not so easy.



Quote:
Originally Posted by Joshua Bunn View Post
All the best Paul with ironing out technical issues. What was the reason to move the secondary forward?


Nice write up Eric. As I'm sure you are aware... one way to find out if it's tilt or colimation is to rotate the camera relative to the scope. If the star shapes, whatever they be, follow the chip (stay in the same place) then you have tilt. If they change place from rotating the camera, then it's likely you have an optical issue. The next issue to be aware of is, is tilt being introduced when rotating the camera .


Josh.
Hi Josh,

the secondary when it arrived was 25mm away from the primary and looked like an ellipse when viewed through the sight tube. I could not see the edge of the secondary closest to the spider either. About a third of the secondary was not visible.


So now to the latest developments. I finally nailed down the correct position of the secondary toward the primary mirror. It took a few hours yesterday to get it perfectly positioned. The problem stemmed from not using a white sheet of paper behind the secondary and then viewing the reflection of the darkened walls in the observatory. I had the secondary skewed a little and not centred correctly. The secondary is enormous too at 110mm, it put deceived me a little too. So I am now happy that I have this correct, but by the time I did a star test it was getting late and I wanted to get home. As you can see in the first image, this is how the out of focus stars in the centre looked before yesterday. The second image is how an out of focus star looks now (still a very small tweak needed but enough to still cause problems with this fast scope). The third images is the corners and centre as seen now and a single sub is the last image which show the vignetting which confirms the collimation error. So another trip down next week at night to give it that final tweak. Next time I take my laptop instead of my iPad.
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  #71  
Old 19-07-2018, 07:22 PM
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Heroic effort on your part Paul.....BUT...seriously? I have to agree with Greg.

This is no bargain basement instrument.

Having to tinker to the extent you describe is damming for Orion UK. I would have sent it back, but suspect that wasn’t an option.

Anyway, looking forward to seeing some high-res imagery from the new machine.
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  #72  
Old 19-07-2018, 07:54 PM
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Peter, I can tell you the angst this purchase has caused me is more than enough to put me off. I'll never go down this path again, the significant cost should equate to perfection. Whilst I am good at solving issues, I can tell you I would rather be imaging flat out, than being able to demonstrate how something should be prepared for delivery. At least I don't appear to have bad optics.

Sending it back was never an option. The cost there and back had me concerned. Not to mention if it would actually come back in one piece or come back at all.

In time will be putting up a full review. Next time I'll pony up and buy a Hercules or Dream Scope.
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  #73  
Old 19-07-2018, 11:27 PM
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Hi Paul

I've been reading your thread from the very beginning and following your story every step of the way! I look forward to seeing your images.
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  #74  
Old 20-07-2018, 04:29 AM
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Quote:
Originally Posted by Paul Haese View Post
Hi Allan, I have been a long time user of CCDInspector. It gives good general analysis which helps to resolve these types of issues. Getting to the site and doing the tweaking has been generally possible during the day at present. Last night I was there but could not complete the final tweaks, which I hope can be done next week.

Hi Paul,
Although your new telescope should have worked perfectly
straight out of the box I don't think that any of the problems you've encountered
will prevent you from turning this telescope into a fine instrument
that will serve you well.
All the right things are there: a carbon fiber tube &
it looks like a top mirror along with proper tube rings
and other accessories.
You know how to use CCDInspector & that should enable you
to adjust your corrector spacing for a flat field & achieve perfect collimation.
The large corrector & focuser should allow you to achieve
a nice even illumination of your camera chip.
Hopefully you'll find that the collimation will hold in all
usable angles for pointing the telescope.
I wish you well & hope to see you produce some fine images in the near future.


cheers
Allan
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  #75  
Old 20-07-2018, 07:42 AM
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Paul, having gone the same way (12” f/4), and even with the experience I have (making, testing and of course collimating Newtonians for more than 40 years) I ended up buying autocollimator. Fast scopes, large chips and small pixels are combination that Devil himself must have invented!
I fully reccomend Catseye XLKP devices. They really work, are made extremelly well, and quite ingenious. I’ll never collimate fast astrograph again without it.
Good luck,
Bratislav
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  #76  
Old 20-07-2018, 08:17 AM
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Got to wonder how these guys are still in business. This is unreal... hope you get it all sorted out but really this thing should work flawlessly out of the box. That's what the price tag is for. But it seems no fcuk's given once it's been shipped.
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  #77  
Old 20-07-2018, 09:18 AM
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Paul perhaps it would not matter which high end Newt you bought, as the delivery trip would likely knock it out of alignment regardless. They can't be sending out non-aligned scopes in this price bracket. I know Tekeskop-Services adjust, on their optical bench, every scope they ship, yet still some arrive mis-aligned. This mainly applies to mirror based systems, like my Edge that I bought from TS. That 110mm secondary has significant mass to be held in place through all the bumps, shakes, speed humps, hard landings etc. Is there any manufacturer that will guarantee a scope will arrive in the state they shipped it? Most importantly, I believe, is their assistance to resolve any delivered misalignment.

TS are presently wrestling with Skywatcher ED150s which arrive from the factory mis-collimated, and since the cell is not designed for user collimation, they now need Syntax to supply collimation instructions which will involve disassembly of the front end to some degree. They discovered this issue because they bench test every scope being shipped out by them.

Last edited by glend; 20-07-2018 at 09:29 AM.
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  #78  
Old 20-07-2018, 10:18 AM
bratislav (Bratislav)
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Most people don't realize how quickly things become sensitive once we up the ante in f/ratio domain. For a given camera (chip size and pixel size) sensitivity goes up with fourth order (*) when we drop the f/stop. (coma goes up with square of f-ratio, but Airy disc also gets smaller and angular field of view also gets larger for given chip)
In plain terms, f/4 scope will be nearly 2.5 times more sensitive to collimation misalignments than f/5 one. f/3 (geometric) as in Veloce astrographs becomes 2 to 3 times more sensitive again compared to f/4 (I'm sure Bert can confirm that!).

And I do agree, no matter who makes the scope, you will have to be confident you can collimate it yourself to perfection. Big primaries, big secondaries, big correctors and focusers simply make things if not impossible, at least extremely hard to keep collimation 100% in check when traveling around the world.

(*) this only applies if pixels are small enough to sample Airy disc; otherwise rule becomes more like cube of f/ratio difference

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  #79  
Old 20-07-2018, 08:39 PM
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Quote:
Originally Posted by bratislav View Post
. Big primaries, big secondaries, big correctors and focusers simply make things if not impossible, at least extremely hard to keep collimation 100% in check when traveling around the world.......
Sorry...couldn’t resisit. My AP305mm F3.8 RHA arrived with perfect collimation
and remains so to this day.
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  #80  
Old 20-07-2018, 08:55 PM
glend (Glen)
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Quote:
Originally Posted by Peter Ward View Post
Sorry...couldn’t resisit. My AP305mm F3.8 RHA arrived with perfect collimation
and remains so to this day.
According to the website the AP 305mm is shipped on a pallet, which normally you would expect to be handled by a forklift, not thrown into cargo holds. And the pallet and shipping is on top of the $22k USD price. It's way over the Orion price point.
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