Any reflector “experts” in England?

[a6400]

Hi,

I have a 16” Explore Scientific scope and I live near Bristol.

I need some help with scope losing collimation and things like perhaps cleaning the mirror etc.

I wonder if there is any companies or people who deal with this stuff up to 3 hours away from Bristol?

I am afraid of doing this stuff by myself.

Perhaps someone could help me with this ofc not for free.

Cheers!

Edited September 24, 2023 by a6400

[John]

Hi,

I'm at Portishead so not far from Bristol. I'm a member of Bristol Astro Society.

I've been using newtonians for many years now so might be able to help. Send me a PM (Private Message) if you like 🙂

 

[Astrobits]

I can also help.  I have made mirrors up to 20" and whole scopes up to 16".  I live about 45 mins drive south of Bristol at Highbridge. PM me for more info

Nigel

[Sunshine]

Welcome to SGL! I see you've clicked the link I provided and joined, you will love SGL!

[a6400]

16 minutes ago, Sunshine said:

Welcome to SGL! I see you've clicked the link I provided and joined, you will love SGL!

Sorry, what link do you have in mind? 😛

[Sunshine]

1 hour ago, a6400 said:

Sorry, what link do you have in mind? 😛

Maybe I have the wrong person, I provided a link to SGL to a new CN member looking for reflector advice in England, I am also on CN.

Edited September 25, 2023 by Sunshine

[a6400]

Anyway still looking for help.

 

For now only need help with cleaning both mirrors.

[Mandy D]

17 minutes ago, a6400 said:

Anyway still looking for help.

 

For now only need help with cleaning both mirrors.

Two members have vrey generously offered their assistance with this, already. Have you responded to them? See their replies, above.

Edited September 27, 2023 by Mandy D

[dweller25]

Hello @a6400
 

You have had offers of help on this site and CloudyNights from people who live close to you.

Is there something in particular that you are looking for ?

 

Edited September 27, 2023 by dweller25

[a6400]

1 hour ago, Mandy D said:

Two members have vrey generously offered their assistance with this, already. Have you responded to them? See their replies, above.

Astrobits didn't reply to my last message sent 2 or 3 days ago.

John decided to back off...

 

So I'am still looking for someone to help me clean mirrors and collimate, that's all.

I'm living in Weston super Mare.

Can take the scope to you or invite if someone can help.

 

[Spile]

I’ve written guides on cleaning mirrors and collimation (link below). Please try them out and if you have any questions, I’d be happy to help you.

[a6400]

8 minutes ago, Spile said:

I’ve written guides on cleaning mirrors and collimation (link below). Please try them out and if you have any questions, I’d be happy to help you.

Thanks but the issue is being able to remove the primary and assemble it back safely.

I've seen some guides on cleaning already.

I'm trying to collimate with a cheshire with a crosshair but this scope has different kind of spiders so I can't really align it with the crosshair.

[Ricochet]

You never align the spider with the crosshair. You align the secondary using the circular edge of the Cheshire/sight tube as a guide, and then align the doughnut of the primary with the crosshair. 

[John]

I'm sorry that I was not able to follow though with my offer to help with your issues but, as I explained in our PM exchange on the other forum, having reviewed the issues that concern you, I realised that my lack of knowledge of the approach that Explore Scientific have used in the design of their dobsonians was likely to prove un-helpful to you and possibly even confusing. 

You may already have seen this thread on this forum from 2014 but it is quite extensive, relates to the same scope that you have and was started by one of our experienced members. It contains a number of tips and modifications that the owner discovered were helpful as he got to know the scope and these might be of use to you as well. Good luck with the scope !

Here is a link to the thread I mention above:

 

Edited September 27, 2023 by John

[Spile]

10 hours ago, a6400 said:

Thanks but the issue is being able to remove the primary and assemble it back safely.

I've seen some guides on cleaning already.

I'm trying to collimate with a cheshire with a crosshair but this scope has different kind of spiders so I can't really align it with the crosshair.

Read the guide on cleaning because it goes through the disassembly process too.

As for collimation as my guide says the reference points are the outside of the secondary, primary donut and edge of focuser. The cross hairs of the Cheshire are a reference point in respect of the centre mark. 

[Astrobits]

I did reply to you pm's. The last one yesterday. Unfortunately I am not always able to reply to messages immediately, I do have other things to do and it might be day's before I can find time to respond. 

Nigel

[Mr Spock]

I've often thought It would be great to have a series of collimation mentors around the country who could help with this. Newtonians are a very common telescope for a good reason and they are capable of so much when correctly adjusted.

Collimation has a steep learning curve. For experienced observers it's an easy task performed on a regular basis; for the inexperienced it can be a nightmare. It's not always easy following online tutorials.

[Mandy D]

@Mr Spock There are so many different tutorials available online, that seem to take many different approaches to explaining the process, it is hard to determine which one is best. I know that Astrobaby offers a guide that a lot of people rave about, but for me it simply does not come across as clear. There are others that talk about A=B, etc that makes it no clearer for me. Don't even mention videos, as I have never found one on anything that helps in the slightest! I finally found a web page that I could get my head around and think I have my 200P near perfect collimation, but really I am not certain. It snaps into focus just like a good refractor, now and with excellent seeing, my Moon photos are very sharp, even before stacking, so it must be close, right?

I have the secondary perfectly centred on the focuser and the Cheshire shows perfect alignment of it's spot with the centre spot on the primary, yet is not concentric with the focuser tube and Cheshire crosshairs. What gives? I'm currently ploughing my way through Suiter: Star Testing Astronomical Telescopes in an attempt to better understand all the elements of collimation. I know that once I understand it properly and have seen a telescope in perfect collimation, it will then seem so simple.

You are right, probably an hour with a mentor and I would have the process licked.

 

[Mr Spock]

28 minutes ago, Mandy D said:

There are so many different tutorials available online, that seem to take many different approaches to explaining the process, it is hard to determine which one is best.

Everyone has their own way, but, someone viewing from the outside can easily get lost. That's why it's better to see it in person.

I follow everything in a sequence, of which the first couple only need to be done once.

1. Check the vane lengths using a calliper
2. Use a concentre to: a) check the position of the secondary under the focuser, and 2) check the alignment of the focuser (it can need collimating)
3. Use a Cheshire / laser to collimate the secondary (re-check at monthly intervals or longer if not in use)
4. Use a Cheshire / laser to collimate the primary (re-check before each session)

Step 2 is probably the most daunting. It is so easy to mess up the secondary and get lost as to how to put it right. It's best left alone if you aren't confident.

45 minutes ago, Mandy D said:

It snaps into focus just like a good refractor, now and with excellent seeing, my Moon photos are very sharp, even before stacking, so it must be close, right?

As long as the optics are in alignment that's what you'll get. The secondary is a flat so there's a little wiggle room left/right/front/back. It's better to have it in the right place of course but as long as that line between the centre of the primary and the centre of the eyepiece is spot on you are good to go.

[Mandy D]

@Mr Spock Thank you. I have seen your guide to this before, but I'm always confused by your reference to a concentre. Googling the term along with astronomy brings up nothing helpful and neither RVO nor FLO seem to list such a thing. What is it and how do I get hold of one? I can see the primary mirror clips in the secondary, as expected.

The vane lengths have been adjusted to be within 0.5 mm of each other.

Cheshire alignment of primary is spot on, as far as I can tell.

All of my Newts have focusers with alignment bases, but I have yet to find and mark the postion diametrically opposite on the inside of the tubes.

[Space Hopper]

You mean this.......?

https://www.firstlightoptics.com/other-collimation-tools/ts-concenter-2-adjustment-eyepiece-for-newtonian-telescopes.html

[Mandy D]

22 minutes ago, Space Hopper said:

You mean this.......?

https://www.firstlightoptics.com/other-collimation-tools/ts-concenter-2-adjustment-eyepiece-for-newtonian-telescopes.html

It appears @Mr Spock and myself are both British! I had not thought of using the American spelling for centre (AKA center).

Thank you!

[Captain Scarlet]

Collimation is the process of aligning the optical elements. In a Newtonian, that means aligning (making coincident) the axes of the eyepiece and the primary mirror. Which in turn means somehow aiming the eyepiece axis directly at the centre of the primary mirror; and aiming the axis of the primary mirror directly back at the centre of the eyepiece tube. Both these two steps can be done independently of the other, luckily.

In a perfectly-collimated Newtonian (using a laser and barlowed laser, as it's easiest to describe):

1. a perfectly-collimated laser-pointer inserted in the focuser tube will strike the primary in exactly the centre (using the tilt of the secondary as the beam-director);

2. (using a Barlow in front of the laser) the reflected shadow of the primary's centre-marker should fall exactly in the middle the face of the inserted laser.

Once you've achieved 1 & 2, the Newtonian is collimated.

Two things, though:

i. notice I've not mentioned anything about "centring the secondary". A Newtonian can be considered collimated according to the definition above (aligning the optical axes) almost regardless of how well-centred the secondary is. The actual _location_ of the secondary only affects illumination levels across the image. A thought experiment: if you place black tape across four edges of the secondary, rendering it rectangular, of if you snap off an edge of the secondary, the scope is still collimated. Obviously, for ideal illumination, you'd like the secondary to catch as much of the returning light-cone as possible, but getting the secondary to appear "round" is far less important than the alignments.

ii. almost all techniques for collimation require the centre-spot of the primary to actually be in the centre. In both primary mirrors I have measured, this was not the case, one grossly so.

Magnus

 

[John]

I think the original poster here has more in mind than just the collimation of the scope. 

[Mandy D]

@Captain Scarlet Thank you. Yes, I understand the arrangement of the elements that should be achieved by perfect collimation. It is perfectly logical. Your description of the laser proces confirms this in my mind. I completely agree that the location of the secondary in space does not affect this element of collimation and now I understand the effect it has on the resultant image, thank you. So, for visual use the centring is not as important as for photographic, because for the latter an even illumination is of paramount importance.

Of course, due to perspective (the far edge being more distant) the secondary should not actually appear circular, but distorted by that perspective. But, as you note the shape is not terribly important and we could use a rectangular mirror here as long as it, at least, covers the section of the light cone at this interface. I think I have a much clearer understanding of what is going on from a practical point of view, now.