Collimation confusion

[bosun21]

3 hours ago, Kon said:

Which part is not ok? I think there might be a bit of tilt.

There is a bit of tilt error but It's more than close enough for visual at low to medium magnification. At higher power the collimation error becomes noticeable.

Edited February 23 by bosun21
Autocorrect error.

[PeterStudz]

8 hours ago, Kon said:

That was my main issue that I couldn't get these equal and in the end I had to remove the spring from the secondary screw.

That was my issue too. Nothing to do with the clips or primary. But I could not get a=b - ie the secondary could be aligned equally under the focuser. 

[bosun21]

I have collimated 8" 10" and 12" Flextube dobsonians and left the springs in place.

[Kon]

9 hours ago, bosun21 said:

Much closer but I definitely wouldn't remove the springs. They are there for a solid reason which is to keep  tension on the secondary mirror holder at all times. This helps the secondary to be held in the correct position and stay there. You can get yourself tied up and chasing your tail with the secondary but never seem to get it just right. The telescope will most definitely be able to achieve collimation with them in place. The fact that you couldn't with them fitted tells me something else is wrong. I just want you to get it bang on for the 12"to enable you and I to draw the views and planetary images from both our 10" & 12" dobsonians. If you can't get it just right i would be more than happy to assist you with it (springs in place) as we are pretty close to each other.

Thanks Ian, I will probably have to take you on the offer as I am running out of ideas. I will message you later.

[Kon]

7 minutes ago, bosun21 said:

I have collimated 8" 10" and 12" Flextube dobsonians and left the springs in place.

I feel that something is not quite right. My money is on the primary not been installed properly (I am not sure about your 10" but the 12" mirror needs to be installed by the user and the previous owner did not have any prior experience with telescopes so I think the issue might be lying there?)). I cannot see anything else being wrong. My 8" (although no flextube) is a 5 min job even if I need to touch the secondary. 

[bosun21]

19 minutes ago, Kon said:

I feel that something is not quite right. My money is on the primary not been installed properly (I am not sure about your 10" but the 12" mirror needs to be installed by the user and the previous owner did not have any prior experience with telescopes so I think the issue might be lying there?)). I cannot see anything else being wrong. My 8" (although no flextube) is a 5 min job even if I need to touch the secondary. 

It's a simple matter of removing the primary and reinstalling it properly and back to it's proper position. You could wash the mirror while you have it out but only if there is dirt on the mirror otherwise leave it. The 12" mirror is easy to remove and replace. I had the mirror out several times with my 12" for modifications.

Edited February 23 by bosun21

[Mr Spock]

I'm sure help is at hand.

Shame we aren't closer. I built my first Newts by hand some 48 years ago, so have quite a bit of experience. I'm not so good at explaining things though - much better at doing!

[Kon]

39 minutes ago, bosun21 said:

It's a simple matter of removing the primary and reinstalling it properly and back to it's proper position. You could wash the mirror while you have it out but only if there is dirt on the mirror otherwise leave it. The 12" mirror is easy to remove and replace. I had the mirror out several times with my 12" for modifications.

ok mirror will go out tonight/this weekend 😟 and see if that will improve things.  Not a spec of dust on it despite being 4 years old (covid hobby and I was told they only took it out 6 times).

42 minutes ago, Mr Spock said:

I'm sure help is at hand.

Shame we aren't closer. I built my first Newts by hand some 48 years ago, so have quite a bit of experience. I'm not so good at explaining things though - much better at doing!

Thanks Michael...it's a shame  as I was at the Peak District last week and I could have brought it with me (but it would have meant that I had to leave the kids behind 🤣). It will be easier to pop up in Oxford and see Ian 🙂.

[bosun21]

If he's had the primary mirror out 6 times in a relatively short period  in addition to not having the required skillset is a perfect recipe for errors to occur. There's a good chance he has maybe changed the primary springs with all his tinkering. He's probably realised that he has messed things up badly hence him selling it at such a good price. Don't worry we'll soon have it as good as new. I also have extra springs that I bought for my 12' should you need them 

 

 

[Mr Spock]

Proper strong springs are always a good idea. Essential if you have one of the GSO sourced Newts.

[Kon]

3 minutes ago, bosun21 said:

If he's had the primary mirror out 6 times in a relatively short period  in addition to not having the required skillset is a perfect recipe for errors to occur. There's a good chance he has maybe changed the primary springs with all his tinkering. He's probably realised that he has messed things up badly hence him selling it at such a good price. Don't worry we'll soon have it as good as new. I also have extra springs that I bought for my 12' should you need them 

 

 

I meant he had it out observing 6 times not the primary 🙂. He told me the collimation is very good but when I checked it was awful. He was using a laser only.  It was a genuine sale of somebody who never got into the hobby.

[Kon]

4 minutes ago, bosun21 said:

I also have extra springs that I bought for my 12' should you need them 

 

Just now, Mr Spock said:

Proper strong springs are always a good idea. Essential if you have one of the GSO sourced Newts.

If I get it to collimate properly, would you advise to upgrade the springs at some point? Does FLO have them?

[Mr Spock]

I don't remember the primary springs on either of my Skywatcher 250s being a problem.

[Saganite]

I certainly had to change the primary springs on one of my 12" scopes. I cannot remember now whether it was a Skywatcher or Meade Lightbridge.   I tend to think it was the  Meade, but any way, it needed collimating every time I moved it into the garden until I put a 'beefier' set of springs under the primary and then it was fine.

Edited February 23 by Saganite
unintended statement in capitals.

[Mr Spock]

Just now, Saganite said:

I tend to think it was the  Meade,

I believe they were sourced from GSO.

[PeterStudz]

 

I guess it could be something to do with your primary. But I had my primary in and out multiple times. Not only that but a secondhand mirror, different mirror cell (I had two) and lots of fiddling with clips and various springs. Nothing with the primary made any difference.

Of course it’s not the same telescope and might not actually be the same issue. But I’m certainly interested to see if you can resolve it another way. 

 

 

[Kon]

12 minutes ago, PeterStudz said:

 

I guess it could be something to do with your primary. But I had my primary in and out multiple times. Not only that but a secondhand mirror, different mirror cell (I had two) and lots of fiddling with clips and various springs. Nothing with the primary made any difference.

Of course it’s not the same telescope and might not actually be the same issue. But I’m certainly interested to see if you can resolve it another way. 

 

 

could it be the secondary holder screw is too long? I remember you had to rework on the Dob you acquired. Did you have to change the secondary mirror (maybe it is a tad thicker?).

I will report my findings as I go along.

[PeterStudz]

17 minutes ago, Kon said:

could it be the secondary holder screw is too long? I remember you had to rework on the Dob you acquired. Did you have to change the secondary mirror (maybe it is a tad thicker?).

I will report my findings as I go along.

The secondary was in good condition. I couldn’t find anything wrong with the actual mirror, so as far as I know it’s the original, along with the holder, screws etc. Although I added Bobs Knobs. 

The primary was in a bit of a poor way. It had impact damage from what could well have been caused by a dropped tool/hex key. And scratches where it looked like someone had desperately tried to rub the damage away! I could easily tell that the primary mirror had been removed as it wasn’t put back correctly - there’s a notch in the mirror cell that should line up with the tube seam. But it had been forced in at another position. 

Interestingly, even with a primary mirror like that the views were surprisingly decent! 

Edited February 23 by PeterStudz

[bosun21]

6 hours ago, Kon said:

I meant he had it out observing 6 times not the primary 🙂. He told me the collimation is very good but when I checked it was awful. He was using a laser only.  It was a genuine sale of somebody who never got into the hobby.

I thought that 6 times was a tad excessive 😂. I must have read it wrong. I actually went to change the springs on my 10" and on removing the mirror I was pleased to see good heavy springs already fitted. It's worth checking though as the 12" mirror is a good bit heavier. Good springs are a must if you want to preserve the accurate collimation. I don't think the central screw on the secondary mirror holder has anything to do with it as they are all standardised parts on an assembly line. I am confident in finding the problem in a matter of minutes and then collimating the scope correctly while taking you through each step.

[bosun21]

6 hours ago, Mr Spock said:

I don't remember the primary springs on either of my Skywatcher 250s being a problem.

On removing the primary mirror on my 10" Skywatcher the springs already fitted were a heavier gauge than the ones I bought to replace them. A pleasant surprise.

Edited February 23 by bosun21

[wookie1965]

When I took my 10" apart to flock it I put a piece of electrical tape on the tube and the primary mirror cell. I had read you need to keep the mirror orientated the same way. Whether that is true or not I dont know but I did it anyway.

[bosun21]

Just now, wookie1965 said:

When I took my 10" apart to flock it I put a piece of electrical tape on the tube and the primary mirror cell. I had read you need to keep the mirror orientated the same way. Whether that is true or not I dont know but I did it anyway.

The tape on the tube is so that the fixing screw holes on the tube line up accurately with the primary mirror cell. The mirror itself can be collimated correctly regardless of the rotation position as it's a parabolic mirror.

[PeterStudz]

I was surprised how changing to a different primary mirror made so little difference to the collimation. Literally a few tweaks and it was spot on again. Those mirrors must be well made. 

When I cut the spring down on my 8” Dob it was a shade over 1mm. That was enough to make a world of difference. It still holds collimation well. Eg I’ve taken it in the car for 1.45 hours over country lanes and nothing had moved. 

[bosun21]

23 minutes ago, PeterStudz said:

I was surprised how changing to a different primary mirror made so little difference to the collimation. Literally a few tweaks and it was spot on again. Those mirrors must be well made. 

When I cut the spring down on my 8” Dob it was a shade over 1mm. That was enough to make a world of difference. It still holds collimation well. Eg I’ve taken it in the car for 1.45 hours over country lanes and nothing had moved. 

That's great 👍. But when you go up to the 10" and 12' the mirror weight increases a substantial amount  requiring heavier gauge springs to maintain collimation.

[PeterStudz]

3 minutes ago, bosun21 said:

That's great 👍. But when you go up to the 10" and 12' the mirror weight increases a substantial amount  requiring heavier gauge springs to maintain collimation.

The spring on the secondary? That’s the one I cut down. Is the secondary mirror really that much heavier? 

PS - the 200p doesn’t have primary springs. It uses grommets instead. 

Edited February 23 by PeterStudz