Pixies

Hi. 

It looks like the mirror needs to be rotated a little more. Can you see how the image of the secondary in the primary is a little off line? The secondary is offset when viewed from the primary and the offset means that it overhangs away from the focuser (which is on the left of your picture assuming it is in line with the spider vanes). So the offset of your secondary should be on the right, in line with the spider vane.

See:

ie - rotate the top of the secondary towards you (in your picture)

Hi.

It looks great. Have you got the shot with the paper removed?

Don't try and tighten the centre screw - you make things secure by tightening up the 3 adjuster screws GENTLY. Be careful and don't go too far. I learnt the hard way - they can actually dig holes into the secondary holder and make rotation impossible.

It does look like there is a 'flat' edge on the mirror (top right in the above picture) - do you see what I mean? Now, your secondary is pretty large, so you aren't worrying about losing part of the image of the primary. I assume the focuser isn't fully in as there was no shadow of it in last night's images.

As per the article by Gary Seronik - as long as you have an image of the whole of the primary and it is correctly centred, that's all you need to worry about for visual astronomy. Any further improvement trying to get the secondary located EXACTLY won't provide any visual improvement. But as you are busy getting the secondary adjusted, you might as well get it as close as possible.

Just now, Ricochet said:

Consider the placement of it before you commit to sticking it to the tube. Most people pair it with a RACI finder so you have to make sure that they don't impede each other. 

Another option is a Rigel Quikfinder, which has a much smaller footprint.

Try this: https://binocularsky.com/newsletter/BinoSkyNL.pdf

23 minutes ago, IB20 said:

I think I paid £10 for SkySafari plus. It’s absolutely on the money with everything I’ve observed. Has great tools like observing lists too. Can’t fault it. It might even be half price right now. 

+2.

I think it's £6 just now, for the plus version.

1 hour ago, Pybo said:

They are my first step back into astronomy....and what a massive difference they've made!

I was using them (10x50) for years before I got a bigger scope. It does help you get used to the sky and with a tripod you can find more than you might think - especially if you can get to dark skies. They are so portable too. No cooling worries.

Try M13 (the great Hercules Cluster), M31 (Andromeda), the Double Cluster in Perseus, M44 (the Beehive cluster), M42 (Orion Nebula) (the last 2 aren't visible at this time of year) The moon, of course. You will be able to see the moons of Jupiter, too.

2 minutes ago, Jamgood said:

Brilliant. Thank you. I shall give that a go and report back.

Thank you for all your help. Very clear and straight forward. 😀

I do have a suspicion that the secondary might need some more rotating to get it perfect. Looking at the shadow of the secondary, the offset isn't quite in line with the focuser.

Cool. Now the secondary is aligned so that the line of sight from the hole in the colimation cap hits the centre of the secondary and reflects down to the centre of the primary (the doughnut is dead centre  on the concentric circles). You won't have to do this again unless your scope takes a whack, or suffers some serious bouncing in the back of a car. Check it now and again though, with a Cheshire.

The next step is to align the primary so that the reflection down that  line of sight comes straight back up to the hole in the cap. So adjust the primary to move the black dot into the centre of the doughnut. This is "Collimation Step 4" in Astrobaby's guide. 

Slacken off the locknuts at the primary mirror end and adjust the main adjuster screws the same as before to centre the dot in the doughnut. You can't be too fussy here - this is what makes the real difference. When you're done, tighten up the lock screws. These will have an effect on the primary alignment too! Use them like a fine-tuning setting and keep the dot centred. You will have to learn how tight to lock them down. Some people hardly bother with them and adjust the primary very regularly. I just do them gently finger tight.

As I said - this last stage is the one that makes the difference and you'll need to check this each time you get the scope out, or at least when you suspect the collimation has slipped slightly. You can do the star test to make sure it's all good.

Yep - well done! You are better at this than me - and I like the teal/yellow ochre colour scheme too!

That's the first stage done. You won't have to do that again unless your are doing some maintenance.

Check the three secondary adjusters aren't slack. Also, remove the paper (don't touch the mirror). Now we can move on to the 2nd stage and adjust the tilt of the secondary and align it to the primary mirror. Your secondary is nice and large, so we don't have to be too exact. Just try your best to get the image of the primary concentric with the edge of the secondary and the focuser.

This is "Collimation Step 3" in the Astro baby guide. You adjust the 3 secondary adjusters by small amounts until the primary image is concentric (ignore the reflections in it for now).

You only need to make small adjustments, and be careful not to start tightening things up. For example: back off on adjuster 1/8th of a turn and tighten another by an 1/8th. Or - back off one by 1/8th of a turn and tighten the other 2 by 1/16th of a turn each. You are trying to tilt the base of the secondary mirror holder around the central screw, without tightening or loosening the whole shebang. You'll eventually see how the adjustments move the image of the primary. 

Let us know when you think you have the secondary aligned.
 

Toy don't have to be dead accurate, just as close as reasonably possible. 

Yep. Slowly does it. Use the Mire de thingy to confirm when it's all concentric. Also, as moonshane said, check that the secondary holder isn't squint. Are the 3 small secondary adjusters all at the same depth, roughly?

Can you try backing off the 3 smaller adjustment screws very slightly, just in case everything has been tightened up too much

You're turning the central screw anti-clockwise, yes? Don't force it if it's stiff.

3 minutes ago, Jamgood said:

I have tweaked it a bit since the last photo and currently have it like this.

Looking better. If you can do the paper thing, you will be judging the secondary mirror, not the image of the primary, though.

Jamgood - we'll do: "Collimation Step 2" from Astrobaby's guide, first.

If you can get the coloured paper as she describes, it does make things look clearer. be careful not to touch the secondary mirror.

Keep the tube horizontal, so you don't drop anything down and damage the primary.

If you loosen the central adjuster screw on the secondary, the secondary will move down the tube towards the primary. You will have to take up the slack by tightening the 3 adjuster screws BY EQUAL AMOUNTS, otherwise the secondary will get quite sloppy. Don't over-tighten - just gently finger tight. You are looking to get the image of the secondary to be concentric to the focuser. You can also rotate the secondary so that it shows it's full open face to your eye - it should appear as a circle (concentric) too. If it looks like an ellipse, it needs rotating. 

As long as you do it little by little (DONT OVERTIGHTEN - just finger tight) you should end up with the image of the secondary central and concentric to the focuser . Mire de Collimation will assist in this. 

OK - that secondary needs to be moved, I'm sure. Do others agree?

I'll happily talk you through it. I'm just feeding the kids, so back shortly.

have a read of these two in the meantime:

http://www.astro-baby.com/astrobaby/help/collimation-guide-newtonian-reflector/

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

The next thing will be the coloured sheets of thick paper. Do you have any?

HI. What is the 'cheshire' you made? Is it a collimation cap? If you are sure that the hole is completely central, that's good. We need to be certain that picture is dead centre of the focuser tube.

If yes to the above, it looks like the secondary is out. Can you re-do the Mire de Collimation circles, so that they are concentric with the focuser tube (the large black outer circle).

The 8" Bresser comes with the Meade-type finder shoe with 4 screws. An ES straight finder will fit, otherwise you can fit a Baader shoe and then use a much larger range of finders.

I fixed the Baader show with just one machine screw (sturdy enough for a large RACI finder). 2 of the old screw holes were covered with the Telrad. The one remaining hole is still to be covered up. Alternatively, you can use 2 of the holes to fix the Baader shoe, if you weren't trying to fit a telrad in the same position.

ALso, you could use some counterbalance weights to balance up the dob instead of trying to raise the base. But I agree - it's a bit odd to build this dob with rings but then not provide enough movement to allow you to use them to balance the scope.

1 minute ago, Stardaze said:

In short, it’s too long with the click lock system for my 16mm nirvana to focus, but only by a mil or two. All my other EPs should focus in theory. The click lock adds around 18mm from memory to the system. 

OK. I think I'll do it one bit at a time when I have a go. In fact, I can probably get the 1,25" click-lock adapter just now.

6 minutes ago, Stardaze said:

All of the 2" EP's focus well out (30--34mm), the 1.25"s are much closer. (16mm-20mm) The Nirvana 16mm is the closest. 

I'm going to see if I can swap the 1.25" reducer. If not, it's not the end of the world as trying to go mostly 2" EP's anyway. 

I see you removed the original Bresser extension tube (the one that everyone nearly throws away inthe packaging). What was the reason for that?

38 minutes ago, Stardaze said:

Of course 😃

It's the faff of working out where your eye pieces gain focus, there's 14mm between my lot.. Hopefully on your version, you don't need an extension section, as that adds 30% cost to it all. I could have gotten away with not having the extension, were it for one EP - I was literally about 1mm out! Did consider just clamping it in, a mil out, but there's no leeway later on should I purchase an EP that focuses closer again. 

Ta,

Most of my EPs seem to focus at quite a distance out. Probably around the outer 25% of focuser travel. Perhaps the 203mm Bresser might be a little more forgiving when it comes to having to get an extension. I'll need to measure thing later on. Still on the budget EPs, so no rush.

Which EP caused the problem? How did the 2" EPs fare?

Hi Stardaze,

I'm looking to something similar in the medium term. Can I contact you later to get some information on how things go?

Cheers

A big dob with a Telrad and RACI finder can hunt down objects pretty well. How bright are your skies? Light pollution can really scupper star hopping.

http://www.astro-baby.com/astrobaby/help/collimation-guide-newtonian-reflector/

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