SOLVED!!! Collimation - how to know when it’s miles off

[Mr niall]

At the risk of hijacking my previous thread - I’ve been out with my skywatcher heritage 130p after a marathon collimating session where I undid everything and redid it from scratch. Having read almost everything there is going, I’m still getting fuzzy unfocused stars at all magnifications, and fuzzy planets with a sort of ghost bouncing around - like I said yesterday - almost like a view through miscollimated bins.

im observing outside in the dark and sessions are about an hour, I’ve only got about 5 mins cool down BUT the sessions are lasting an hour or so...

from what I’m reading it seems like the inability to focus is a symptom of “really really bad collimation” so I was wondering if I went through my process  if anyone could give an opinion as to where I could go so massively wrong? Currently as I turn the focusser, I get closer closer closer- then it goes the other way past focus. I have not had a single experience of pinpoint stars with this scope anywhere across the FOV. Honestly I’m not a million miles off packing it up and putting it in the loft. I’m getting flaring on brighter stars too. 

• Measured the length from front of tube to middle of focusser as a reference for where to put the middle of the secondary.
• adjusted secondary - both with a paper baffle in the tube and without, looks pretty much in the middle of the focusser (used a collimation cap).
• adjusted tilt so image of secondary looks circular - took photo to check, then drew a circle over it on computer. Not perfect but pretty close.
• adjusted so I can see all three primary mirror clips in secondary.
• adjusted dotted primary so it seems perfectly in line with collimation cap, and middle of secondary image too for that matter.
• take it outside, look through it. Consider smashing it up.
• bring it inside, swear to never use it again
• repeat process next clear night.

im guessing I’m going massively wrong somewhere, massively - but I just don’t get it. Like I said, I’m trying different EPs and the effect is identical with all - just more pronounced at higher mags; so I’m sure it’s a system issue. Star tests, well, they’re not that bad, pretty even concentric rings all round (tube currents make them wobble a bit) as I get close to focus though it looks just like one of those speckle interferometry images which is pretty but not encouraging. Very clear diffraction spike too, nice and straight.

im just using a collimation cap at the mo but have a Cheshire on order (sold the last one) - in honesty though the outcome was the same when I just used the Cheshire too. I have also tried a really nice BST starguider 25mm with no noticeable improvement.

So is there anywhere I can still go massively wrong in the process that is introducing some catastrophic error. I’m led to believe this level of quality is indicative of Olympic level idiocy, but I’m stumped. Any ideas?

thanks.

[wookie1965]

Use Astrobaby`s and this site http://www.schlatter.org/Dad/Astronomy/collimate.htm I was the same first time took me two days lots of swearing until found these made it much simpler.

[cletrac1922]

Why need to touch in first place

What you using to collimate?

I use laser collimator

First adjust secondary mirror, so that laser led is centre of the primary mirror

Should be a tiny dot on primary, indicating centre

Just use 3 outside screws of secondary mirror, never loosen centre screw, as secondary mirror can slew around, and then in all sorts of issues

Once have secondary aligned, then slightly loosen 3 locking nuts for the primary

Using the disk centre of laser collimator, adjust the 3 other screws base of the mount

The laser beam will disappear completely, when in centre of the collimator disk

Tighten locking screw, ensuring primary mirror does not move out of alignment

Unless, you transporting your scope regularly, then once aligned, no need to touch again

I am out couple of times per month with my astronomy club, doing school, scout/guide groups presentation, and rarely need to adjust on my 10" collapsible dob  

[Mr niall]

Thanks - it arrived miscollinated so has had to be adjusted. I’ve read some mixed reviews about laser Collimators... But in all honesty I don’t think I’m ready to spend 85% of the cost of the scope on a tool to make the scope work!

[happy-kat]

It's a fast scope f5 so it won't be a centred circle. There is a picture of a fast scope offset on astrobaby's site have a look at that in relation to what you adjusted.

[Alan64]

This is the secondary scene of my 150mm f/5 Newtonian, and snapped through a collimation-cap...

You want your own to appear very similar.  Note the secondary off-set.  That occurs automatically during a normal collimation procedure.  You don't have to adjust or tweak anything to effect the off-set.  Also, know that the shorter, the faster, the Newtonian, the more difficult it is to collimate.  But an f/5 is not too terribly difficult.

[happy-kat]

Also make sure when raising the top section that it locks/snaps into position.

[Moonshane]

Sounds more like a warm tube to me although you should see some improvement by the end of the sessions.

Is the eyepiece OK in other scopes if you have them? Is the secondary tight?

 

[Louis D]

How about during the daytime?  Can you bring distant objects into focus?

[Buzzard75]

Not sure it makes a huge difference in this particular case, but the first step should be to make sure that the secondary is centered in the tube assembly itself. Measure the length of the spider vanes from the inside of the tube to the center of the secondary stalk screw. Tighten or loosen the vane screws as necessary so they are equal in length, yet firmly holding the vanes in place. Then continue as you did to center the secondary in the focuser, adjust it for tilt, get the three clips on the primary, align the primary. If it looks like it's collimated then it's collimated. If you're getting fuzzy stars there's something else going on. As suggested, it could just be thermals. Also recommend you attempt to focus during daytime on distant objects. I used a combination of collimation cap, Cheshire and laser for my initial collimation. After that I use the laser and check with the collimation cap during setup for the night and fine tuning. I only ever do a major recollimation when it's absolutely necessary. Most times I just have to adjust the secondary slightly and the primary as I have a truss type that gets disassembled every time.

Astro Baby's guide:

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

[Ricochet]

5 hours ago, happy-kat said:

It's a fast scope f5 so it won't be a centred circle. There is a picture of a fast scope offset on astrobaby's site have a look at that in relation to what you adjusted.

The secondary itself will appear to be centred under the focuser but the shadow of the secondary in the reflection of the primary will appear to be offset. So in Mr Niall's list steps 2/3 the secondary appears centred, in step 5 the secondary shadow is offset.

17 minutes ago, Buzzard75 said:

Not sure it makes a huge difference in this particular case, but the first step should be to make sure that the secondary is centered in the tube assembly itself. Measure the length of the spider vanes from the inside of the tube to the center of the secondary stalk screw. Tighten or loosen the vane screws as necessary so they are equal in length, yet firmly holding the vanes in place. Then continue as you did to center the secondary in the focuser, adjust it for tilt, get the three clips on the primary, align the primary. If it looks like it's collimated then it's collimated. If you're getting fuzzy stars there's something else going on. As suggested, it could just be thermals. Also recommend you attempt to focus during daytime on distant objects.

Astro Baby's guide:

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

The Heritage 130p only has one vane so figuring out whether the secondary is properly positioned in the tube might be more difficult. Hopefully the offset is built into the attachment of the mirror to the holder.

15 hours ago, Mr niall said:

 

• Measured the length from front of tube to middle of focusser as a reference for where to put the middle of the secondary.
• adjusted secondary - both with a paper baffle in the tube and without, looks pretty much in the middle of the focusser (used a collimation cap).
• adjusted tilt so image of secondary looks circular - took photo to check, then drew a circle over it on computer. Not perfect but pretty close.
• adjusted so I can see all three primary mirror clips in secondary.
• adjusted dotted primary so it seems perfectly in line with collimation cap, and middle of secondary image too for that matter.
• take it outside, look through it. Consider smashing it up.
• bring it inside, swear to never use it again
• repeat process next clear night.

 

Those steps look ok. With the added Cheshire you can check the Cheshire cross hairs align with the doughnut in step 4.

The ghosting with planets is likely in the eyepiece due to reflections off lenses. Condensation can do this as well but only after the lenses have cooled somewhat.

In the halo around a very bright star or a planet can you see three (maybe four) dark radial shadows? If so masking the edge of your primary mirror will tidy up the stars a bit.

[Mr niall]

Hi all thanks for the suggestions. I don’t think the eyepieces are the source of the problem (as I’ve tried so many of them) although their mediocrity may not be helping!

just tried various distance, up to about two miles - same issue, can’t quite focus.

tried a photo through collimation cap, not very easy as it turns out, but you get the idea!

thanks again all.

 

[happy-kat]

This is mine (cropped) looks similar to your image.

Have you tried moving the eyepiece in and out, where are you running out of focus is it inward or outward focuser travel?

[Mr niall]

Thanks - nah thought of that, focus point is generally in the middle ish of the range - can go a fair way either side with all my eyepieces.

actually @FLO - you’ve probably fixed bajillions of these, do you have any suggestions?

[happy-kat]

Just crudely ran Al's collimation aid over mine, though not sure if it even should be used as it is for SCTs.

[Mr niall]

@happy-kat Just had a go myself - not as close as yours, but still doesn’t look bad enough to explain what’s going on...

 

[Moonshane]

What's the smeary blur in the bottom left hand corner of the last image?

[Moonshane]

The secondary unless way out (yours is not) has almost no effect on the visual image.

[Mr niall]

13 minutes ago, Moonshane said:

What's the smeary blur in the bottom left hand corner of the last image?

Think that’s just a reflection from the camera.

[Moonshane]

Ahh. Just trying to rule things out.

[Peter Drew]

The final collimation looks plenty good enough to produce a decent image. The next thing I would check is the tightness of the primary mirror. It should be loose enough to move about with little finger pressure.  ?

[John]

1 hour ago, Peter Drew said:

The final collimation looks plenty good enough to produce a decent image. The next thing I would check is the tightness of the primary mirror. It should be loose enough to move about with little finger pressure.  ?

I agree. Any improvements beyond that are about getting the last 10-15% of performance.

If images are still blurred then I'd suspect something else is amiss. I noticed some finger prints on the secondary mirror surface in the top photo but those don't look critical.

Interesting that the star diffraction patterns look not bad until the point of best focus is reached and then they go like "speckle interferometry images" ?.

 

 

 

[Mr niall]

3 minutes ago, John said:

I agree. Any improvements beyond that are about getting the last 10-15% of performance.

If images are still blurred then I'd suspect something else is amiss. I noticed some finger prints on the secondary mirror surface in the top photo but those don't look critical. Are you able to go from inside focus, through sharpest focus (such as it is) and then on to outside focus with the scope as it is ?

Presumably the blurring gets even worse either side of focus and beyond

 

 

Yes there’s a smidge of smudging (it has had a lot of attention over the last few months!) but it’s only minor and I’m not going to risk cleaning it.

primary is averagely tight, yes can get either side of focus easily enough!

[John]

Which star(s) did you star test on, with which eyepieces and after how much cool down time ?

Did you notice any dew on either the primary or secondary mirror and were your eyepieces cold ? (cold eyepieces can mist as soon as your eye gets close to them or if you breathe on them accidently before putting your eye to them)

Dew / fogging / misting could account for what you are seeing - which is why I'm asking.

Sorry for all the q's - just trying to eliminate stuff !

 

[Mr niall]

Thanks all - I’ve just cracked it! I measured the tube arms when extended and found one was slightly shorter than the other - the plug at the end was slightly unseated - even though it’s been locking tight when extended I think I’ve been adjusting it to a slightly different angle every time and heavy EP’s / shifting it around in the field /opening and closing it / has been knocking it off alignment as I’ve been repeatedly collimating it to the wrong place. To Be honest I can’t believe I didn’t notice it sooner...

fixed, quick test on Altair , Deneb and Saturn - perfect!

Thanks for your help everyone! What a relief!