Collimation help

[harpy]

So I received my collimation cap. This is the image I see when I look through  the focuser  on sky watcher heritage 130p.. 

I initially thought it was out of whack but when I turned the focuser fully in I think it looks good. Would I be right in saying it doesn’t need collimation going by the attached picture?

 First pic is when I didn’t have the focuser knob twisted in fully and looks slightly off but second is with it twisted in fully and looks ok would people agree??

Edited July 17, 2020 by harpy

[Pixies]

yep - that's not far off.

Secondary looks good. You just need to adjust the primary so that the dot is centered in the doughnut.

[Ricochet]

When you don't have the focuser fully in, is there play in the focuser such that it can move to where it looks collimated? In this case perhaps the standard modification of ptfe tape on the threads will help. Alternatively, as you turn the focuser, does it drift in and out of collimation depending on the angle that the focuser has been turned? (i.e. One full turn from fully in it is in collimation again. )

[Pixies]

35 minutes ago, Pixies said:

yep - that's not far off.

Secondary looks good. You just need to adjust the primary so that the dot is centered in the doughnut.

Sorry - I mis-read the original post. I was only looking at the first picture (I blame the phone browser). Please ignore

[AstroMuni]

1 hour ago, harpy said:

 First pic is when I didn’t have the focuser knob twisted in fully and looks slightly off but second is with it twisted in fully and looks ok would people agree??

A lot of the cheaper scopes have a lot of play in the focusser, hence the effect you are seeing. As most of your observation would be done when the focusser is around half way out (check where it actually gets into focus), I would suggest you check if the collimation looks right at that point.

[harpy]

52 minutes ago, Ricochet said:

When you don't have the focuser fully in, is there play in the focuser such that it can move to where it looks collimated? In this case perhaps the standard modification of ptfe tape on the threads will help. Alternatively, as you turn the focuser, does it drift in and out of collimation depending on the angle that the focuser has been turned? (i.e. One full turn from fully in it is in collimation again. )

 There’s a bit of play but not much doesn’t take it out of collimation.

Yes just checked that each 360  degree turn of the focuser and it comes back into collimation.

[harpy]

49 minutes ago, Pixies said:

Sorry - I mis-read the original post. I was only looking at the first picture (I blame the phone browser). Please ignore

No you replied to what I had posted first, I edited then , so I think you replied just as I had edited it.

[Ricochet]

34 minutes ago, harpy said:

 There’s a bit of play but not much doesn’t take it out of collimation.

Yes just checked that each 360  degree turn of the focuser and it comes back into collimation.

So it's in collimation every 360° and varying amounts out at all other angles? It sounds to me like the focuser is eccentric, personally I think I would talk to your supplier about getting it replaced. Before, you do though, take the collimation cap out and reinsert it at a different angle to check that the fault is with the focuser, and not the collimation cap. 

[harpy]

Yeah it when I turn the focuser it moves a bit it’s doesn’t go completely out. It might go out to the edge of the circle and back in again each full rotation.

[harpy]

19 hours ago, AstroMuni said:

A lot of the cheaper scopes have a lot of play in the focusser, hence the effect you are seeing. As most of your observation would be done when the focusser is around half way out (check where it actually gets into focus), I would suggest you check if the collimation looks right at that point.

Ok, I’ll try this am I best waiting until night time and looking at the moon or something and seen when it’s at best focus and adjust from there. Would different objects come into focus at different points? 
i noticed when I take out the collimating. cap and turn it  and put it back in the the collimation is off so it could be an issue with the cap as well . 

[Ricochet]

1 hour ago, harpy said:

i noticed when I take out the collimating. cap and turn it  and put it back in the the collimation is off so it could be an issue with the cap as well . 

In this case it sounds like the cap is at fault, not the focuser. A replacement cap might solve the issue, so I wouldn't touch the collimation of the scope at this stage. 

[harpy]

23 minutes ago, Ricochet said:

In this case it sounds like the cap is at fault, not the focuser. A replacement cap might solve the issue, so I wouldn't touch the collimation of the scope at this stage. 

Cool thanks I’ll order a new one and hold off doing anything to it until I get it. I think it’s meant to be a bit clear tonight so I’ll try a stat test to see how it looks..

[Erling G-P]

That the collimation changes when you rotate the cap, suggests to me that either the hole in it isn't centered, or that the cap fits so badly in the focuser that it can move around.  Unless it's the latter, I can't see the cap explaining that collimation changes when you move the focuser - after all, it isn't rotated when you do that.

[AstroMuni]

On 18/07/2020 at 12:17, harpy said:

Would different objects come into focus at different points? 

Short answer is yes, but as we are talking astronomical distances here, it wont vary much, probably a fraction of a turn on the focusser. But if you change the eyepiece then it would need refocussing ofcourse. Hence people like to buy parfocal eyepieces to make life easier.

[harpy]

Ok me again 😳..

i got a Cheshire collimator and have the below results now I think is looks ok but.
Primary looks ok to me , I can’t see the secondary clips but am I correct in saying I shouldn’t be seeing the secondary clips when using the Cheshire?? 

[harpy]

Just another question in addition to the above on how the collimation looks.

When using the chesire I noticed the movement in the focuser that was mentioned earlier in the post. So I just get white tape and tape that around the thread below the hexagon part o the focuser and just screw it back in? Does the tape not shed bits into the telescope when focusing in and out from tearing with the threads?

[Pixies]

Use plumbers PTFE tape. It's very thin and stretchy - almost like applying layer of paint. It's used in plumbing joints to make them waterproof. As you screw down, it will be pushed into the threads.
https://www.screwfix.com/p/ptfe-tape-12m-x-12mm/76841

 

 

 

Edited August 2, 2020 by Pixies

[harpy]

1 hour ago, Pixies said:

Use plumbers PTFE tape. It's very thin and stretchy - almost like applying layer of paint. It's used in plumbing joints to make them waterproof. As you screw down, it will be pushed into the threads.
https://www.screwfix.com/p/ptfe-tape-12m-x-12mm/76841

 

 

 

Brilliant thanks pixies ill try get some of that tomorrow in. hardware shop.. that's a really good video, might have to start on a light shroud next.

 

Does the collimation look ok  to you? ill probably be able to get a more accurate idea once I have the tape on as well

 

Edited August 2, 2020 by harpy

[Ricochet]

17 hours ago, harpy said:

Ok me again 😳..

i got a Cheshire collimator and have the below results now I think is looks ok but.
Primary looks ok to me , I can’t see the secondary clips but am I correct in saying I shouldn’t be seeing the secondary clips when using the Cheshire?? 

Whether you can see the edge of the primary and/or clips depends on how far in or out you have the cheshire when you are collimating. Seeing those clips is not essential, the most important part is getting the crosshairs, the doughnut and the reflection of the hole at the top of the cheshire all lined up. For collimation to be absolutely perfect then everything should also look circular and symmetrical either side of a line running in the plane of the focuser as shown in the image below. Your focuser is at the top right, marked by the red F, and the centre line is extended from that point. we can see that the "top left" secondary shadow is slightly larger than the "bottom left" secondary shadow, so there is room for some minor improvement, but I think how you have it now is good enough for use, and I wouldn't worry about trying to improve it. 

 

[harpy]

Thanks ricochet. Much appreciated.

[RT65CB-SWL]

That looks pretty damn close to me... and well @harpy done if this was your first attempt.