Imaging with the 130pds

[Stub Mandrel]

10 hours ago, dyfiastro said:

Hi everyone

I have spent the last 3 days going over this multiple times and getting the same result.
The scope has been collimated multiple times (as far as I can tell from the guides) and I cannot seem to get the illumination even through the whole travel of the focuser.

I have limited the amount of tilt by counting the turns on each of the three grub screws and checked to make sure that the secondary is round, central and the three holders for the primary are all in view.

The illumination still uneven and travels from one side to the other, I have tried allsorts and always seem to get the same result at various different amounts. This is the latest result (Flat frames taken and equalised in photoshop)

Here is the focuser all the way in

And all the way out

Any suggestions and advise would be great, I am sure its something simple but its really starting to frustrate me now.

Thanks in advance

Ha! My 150PL is doing exactly the same at the moment. As said above, tilt in the focuser movement relative to the alignment with the centreline through the secondary mirror. If the tube and focuser are truly at right angles then the secondary may have moved too far down or up the tube with repeated collimation (if you're like me and you always adjust in the same direction...)

[Stub Mandrel]

This is what I mean - exaggerated of course - if every time you collimate you tend to tighten the screws the mirror will 'creep' down the tube, and even if you still line up on the centre of the secondary you will have to tilt it backwards to keep collimation. That means the centre point  will move back and forth as the focuser moves up and down. Hmm; it will also affect sharpness of focus across the image so worth correcting.

[alacant]

3 hours ago, Stub Mandrel said:

line up on the centre of the secondary

Hi. At f5, the secondary should not be centred. Centre, yes. Then displace. It looks something like this. HTH.

 

[wimvb]

44 minutes ago, alacant said:

Hi. At f5, the secondary should not be centred. Centre, yes. Then displace. It looks something like this. HTH.

 

Why not? This seems counterintuitive.

[Stub Mandrel]

Presumably because the light cone is wider where it hits the lower side of the secondary, but I don't understand the diagram. If 1 & 2 are the focusser, they should align with the direction of displacement.

[dyfiastro]

Thanks for the replies everyone. I have spent a good few hours trying to get this sorted an still failing.
I stripped the scope down again and remeasured and squared the focuser again but still no luck.
Tomorrow is another day and will attempt again to get it sorted. The scope was a stinker from the moment I got it, just about every scew was loose and I seem to be spending more time getting it right than using it.

I would love to just leave it and let the flats correct it however I know I will never be fully happy until I have sorted it, plus when using barlows etc.. I do tend to use various different parts of the focuser.

Thanks again everyone for all the help

[wimvb]

6 hours ago, Stub Mandrel said:

Presumably because the light cone is wider where it hits the lower side of the secondary, but I don't understand the diagram. If 1 & 2 are the focusser, they should align with the direction of displacement.

As far as I know, when you cut a cone in a slanting direction, you get an ellipse (= conic section) the size and shape of the secondary. As you, I also don't understand the diagram. And since the diagram should show the view through the focuser, 1 and 2 can't be the focuser.

As for centering or not centering the secondary, I follow this text for collimation:

http://garyseronik.com/a-beginners-guide-to-collimation/

 

Edited December 10, 2016 by wimvb

[alacant]

9 hours ago, wimvb said:

also don't understand the diagram

Hi. I think one only obtains a regular ellipse -the shape of the secondary- by taking a section through a cylinder. A conic section -the light from the primary- has the minor axis displaced toward the 'fat' end of the cone. I can only explain it by doing it:

[Stub Mandrel]

Wim is right (and I'm wrong) the conic section is an ellipse - but the 'centre' does not lie on the axis of the cone. This is the displacement required.

But looking at the links and various diagrams, if the view of the mirror looks right then the displacement is right.

[CraigT82]

I think 1&2 are supposed to be the reflection of the focuser in primary, they're in the wrong place though, should be at the 9 0'clock position in that diagram.

You shouldn't need to do any 'displacing' the offset is built into the secondary assembly. 

I think the issue with he shifting illumination is due to the focuser not being square to the light cone?? 

[dyfiastro]

Thanks everyone for the help and replies.
I have battled with this for another few days and even rechecked the focuser etc...
I am either missing something obvious or something is not right still.

Going to have to leave as it for now but really not happy in doing so.

 

Thanks again everyone

[spillage]

I am having the exact same issue with my 150pds. Have done another collimation and just waiting for a half clear sky to test. Sure the fault is all mine after I stripped it to flock the thing..

[Thalestris24]

Hi

Astrobaby's guide is pretty definitive.

Louise

[abhoriel]

Hi, just a quick question. I'm thinking of getting a 130pds (instead of an ED80 for example). One of the disadvantages cited for a Newtonian is the need to collimate it. Is it really that much hassle? This scope is certainly faster and cheaper than the ED80, and I quite like the spikes!

[spillage]

5 minutes ago, abhoriel said:

Hi, just a quick question. I'm thinking of getting a 130pds (instead of an ED80 for example). One of the disadvantages cited for a Newtonian is the need to collimate it. Is it really that much hassle? This scope is certainly faster and cheaper than the ED80, and I quite like the spikes!

Hi abhoriel,

 

It just one of those things that seems really daunting but after a couple of time you wonder why. Just need to give it time for the penny to drop on what you are looking at and what needs doing. I you can loosen and tighten a screw then you will be fine.

I would recommend a cheshire collimator rather than a laser one.

[abhoriel]

9 minutes ago, spillage said:

Hi abhoriel,

 

It just one of those things that seems really daunting but after a couple of time you wonder why. Just need to give it time for the penny to drop on what you are looking at and what needs doing. I you can loosen and tighten a screw then you will be fine.

I would recommend a cheshire collimator rather than a laser one.

 

thats good advice on the collimator. Thanks very much

[al-alami]

Hi all,

Interesting question.  Considering I am using the scope to image, should I be using a 2" collimator or does it not really make too much of difference?

Thanks

[spillage]

30 minutes ago, al-alami said:

Hi all,

Interesting question.  Considering I am using the scope to image, should I be using a 2" collimator or does it not really make too much of difference?

Thanks

Most are 1.25" and some come with a 2" adapter. As long as everything is secure it will be fine.

[wimvb]

6 hours ago, spillage said:

Hi abhoriel,

 

It just one of those things that seems really daunting but after a couple of time you wonder why. Just need to give it time for the penny to drop on what you are looking at and what needs doing. I you can loosen and tighten a screw then you will be fine.

I would recommend a cheshire collimator rather than a laser one.

Four actually: two on the primary mirror, and two on the secondary (strictly, you don't have to touch the third) 

As for the laser collimator. It has its benefits if combined with a barlow, if there is a center mark on the primary.

http://garyseronik.com/a-beginners-guide-to-collimation/

http://garyseronik.com/collimation-tools-what-you-need-what-you-dont/#more-165 (check further down, at option #5; also the link to Nils Olof Carlin's article)

[Adam J]

7 hours ago, abhoriel said:

Hi, just a quick question. I'm thinking of getting a 130pds (instead of an ED80 for example). One of the disadvantages cited for a Newtonian is the need to collimate it. Is it really that much hassle? This scope is certainly faster and cheaper than the ED80, and I quite like the spikes!

It was has been my first scope and I have not regretted it for a second. To my eye the whole colimation thing is a fuss about nothing, if you are at all technically minded as most of us tend to be it wont be an issue for you at all. It comes well below polar alignment and image processing in terms of difficulty in my opinion.

[alacant]

7 hours ago, Adam J said:

whole colimation thing is a fuss

+1. I think it's the accompanying explanations -written instructions- which put the fuss into it. If someone had given just a one liner, get a Cheshire and make it look like this, I for one would have got there quicker. HTH.

[Adam J]

Here is 18x600s subs with my cooled 550D and Baader 7nm Ha filter.

I really am looking for some advice on this as I am unsure if I have over processed it. I dont know if I should add more Ha or get the OIII next...The Ha is the most important layer as ill re-use it for luminescence later. problem is that I dont think that I have resolved much detail here as the seeing was not great when I collected this data.

I posted this in the processing section of the imaging forum also but did not get much of a response so thought I would try my fellow 130PDS users. I have a couple of versions processed using different techniques, thoughts?

Edited December 29, 2016 by Adam J

[dyfiastro]

Hi everyone.
Thought I would post a quick update to say that I think I am finally getting somewhere.
Now at this point I am not 100% sure where thing have gone wrong but once I have everything completely sorted I should have a better idea.
I got a laser collimator for Christmas and within 5 minutes I have got better results than what I have been getting for the last few weeks using the Cheshire.

Last night was the first chance in a few weeks to get out with the scope and the first time since trying sort the issues out.
My issue with my spider vanes look to be fixed and this was also the first time I had shot using 600s subs (in less than ideal conditions).
I would have have liked to get more data but did not have the time however I am pretty happy with the result as first test.
Will be returning to this target for more data and may even attempt even longer subs to get some of the fainter bits.
trying to figure out the white balance is something I am still having issues with but being colour blind makes it little bit tougher as well.

8x600s @ ISO800

 

 

[Adam J]

And now with some OIII

8 x 900s ISO 1600 OIII - Blue

16 x 600s ISO 800 Ha - Red

Did not bother with any calibration frames.

Posted in imaging section too but I like to share with my fellow 130PDS users

Edited December 30, 2016 by Adam J

[Spaced Out]

21 hours ago, Adam J said:

And now with some OIII

8 x 900s ISO 1600 OIII - Blue

16 x 600s ISO 800 Ha - Red

Did not bother with any calibration frames.

Posted in imaging section too but I like to share with my fellow 130PDS users

WOW !!