Need some advice on collimating a 72ed

[AstroNebulee]

5 minutes ago, WolfieGlos said:

Hi Lee,

I hope so! I feel like it's been a long time, a lot of testing and tweaking. Not helped by the late nights at the moment either haha.

I have a stock Canon EOS 77D. Correct, it is supposed to be 55mm for the Stellamira too and I started out with no spacers albeit with the standard 72ED push fit and a faulty t-ring which wobbled. These have since been replaced with a screwed fit and a Takahashi T-ring, which has no give in it at all.

On my first target (using the original push fit and faulty t-ring) with the 72ED, which was M51, it reports a 63% tilt in ASTAP and actually looking at the individual subs it is quite clear that the stars are very eggy, and to me ASTAP is reporting it correctly. As M51 was cropped quite a lot it's hard to see it in the final image (which I'm quite happy with!), but it is there, and without cropping it is very evident and from the star patterns suggests the backfocus needs increasing. That's why I have been adding spacers.

 

Since I have been trying to collimate, I could actually try removing all spacers as well and see what that does.....thanks for that thought, will give it a shot and see what happens. But at the moment, my subs definitely show eggy stars, not so much of a problem if I'm cropping the image down like above, but a full framed target (i.e. Andromeda, NA, Veil nebulae, etc) will cause me big problems.

The below test image from Markarian's Chain shows it quite well with only the very extreme edges cropped off. Not a great image as it doesn't have many frames but taken as an example to see how bad it would be on a full framed shot. The individual subs report anywhere between 45-58% tilt, so similar to M51 above. When Andromeda rises into view again I intend to frame it diagonally from corner to corner to make it fit, but based on the below it won't be great. The bottom right corner is so bad the stars appear out of focus.... I would almost be forced to do a Mosaic.

Markarians Chain was the last one I took with no spacers, push fit and faulty T-ring, I got into contact with FLO afterwards who have been VERY helpful, and since those items were replaced (and spacers added) the tilt values and eggy stars have reduced but they are still evident.

I'm convinced it's in the focuser so will continue with it, I guess you're right, perseverance will get me there in the end.

Cheers,

Chris

 

 

Hi Chris 

Yes it's most likely in the focuser side of things and it your dslr or connections. Once you get your laser collimator corrected it will be so much easier. 

I agree the late nights won't be helping with your issue but the evenings will start pulling in very soon 😊

FLO are extremely helpful and helped me in the past with tilt issues the collimation procedure and introducing a tilt adjuster to my zwo asi294mc pro sorted it much better. 

You will get there and the sense of achievement will he rewarded by your great images. You are getting there and finding the solution it does take small increments ad tweaks each time. 

Cheers 

Lee 

[Sien]

@WolfieGlos

Are you using a field flattener? because without one your stars will appear "eggy" around the edges of the frame regardless of what you do. Field rotation due to polar alignment error, focuser slop from the weight of attachments and tracking accuracy can all add fuel to the fire. I'd suggest taking some short exposures of stars and checking individual subs. Periodic errors in your mount will introduce minute star trailing that will affect the end result once you stack (and wind, orientation of the scope in the sky, weight of cables etc can all contribute). Apologies if I'm preaching to the choir

I found the cheshire quiet helpful to eyeball things as I went along and made my adjustments. As I mentioned previously, in my case I had to reset the orientation of the objective lens to get things right.  I'll still be tinkering away long after this post!

While software is useful for analysing what's going on, you should trust your own better judgement too, how happy are you with the pictures, can I get away with cropping 5% or more of the frame etc.

Edited July 26, 2022 by Sien

[WolfieGlos]

Hi Sien,

Yes, using a field flattener 🙂 

Agreed it's not best to rely on just the software, but I could see the eggy stars for myself. I do usually crop the images, but a full frame shot (i.e. M31 will fill my entire frame) will show up the problems.

It's been a while since we were posting above, but an update on what happened to me. So I was in constant contact with FLO support about this, and in the end to their credit they actually took the scope back under warranty to have it checked over. I now have it back, and whilst I haven't been informed exactly what was wrong, it did require adjustments and correcting, and is now working very well! 😄 

Whilst I have only just had it back and have used it so far for only 1 nights worth of imaging, my tilt value is very low (varies from 2%-8% across 150 subs....MUCH better than previous 25% and higher). But this new reported tilt value may also be off slightly due to backfocus, as I can see eggy stars in the far corners. I have a 5mm spacer added already, and it looks like it needs more as the streaks are inwards, so I will be continuing to alter this in the coming days with the predicted perfectly clear skies we have here (and typically a near full Moon......). But if the report from the ASTAP software is showing the below values with incorrect backfocus, (Siril gives a very similar reading too) then (in theory) improving the backfocus should make the corners better and lower the reported tilt. 

However, if this is the worst tilt that I get from now on, then I'm happy!

 

[Sien]

Hi @WolfieGlos, wondering how you've gotten on since? While my issues have improved substantially I'm still fighting with some eggyness in the corners, I'll probably try bumping my backspacing to the 60mm mark and see how things are looking from there.

[WolfieGlos]

Hi @Sien, erm, sadly not very well!! That first night when I had the scope back was near perfect. I should have left it alone, but I tried varying ranges of spacers and camera rotations and I am back to square one, with tilted corners varying from 15-25%. Annoyingly in the same corners as previous.

I’ve also purchased an Astro modded dslr; a canon 800d which has the same resolution as my stock 77d, and I get the same problem in the same areas of the image. So I know it’s not the camera and FLO fixed a problem in my scope, and so it must be in my imaging train somewhere. I didn’t try going up to 60mm backfocus, I stopped before then as it got worse the more spacing I added. 

But to be honest, I’ve given up trying to fix it for now and I’m accepting eggy stars in the corners and cropping the worst parts out. Not the result that I want, but I also want to image rather than waste clear nights solving problems! 

Funnily enough I saw this today on FLO’s homepage showing new items, which I’m going to order and see if this finally sorts it out. There’s also an M48 option, but I’ve queried with FLO and the M42 option fits over the threads on the stellamira flattener.
https://www.firstlightoptics.com/adapters/astdym_m42_tilt_adjuster.html

I have clear skies predicted later this week so I will test it if I get it before Sunday, but otherwise I won’t be able to test until the end of October 🙈 

What have you been trying to remove the tilt and eggy stars? 

[Sien]

That sucks, hopefully you can figure it out eventually. I think I'll pick up one of those tilt adjusters you linked just to have handy.

Mainly what was laid out in this post (adjusting focuser via cheshire, adjusting the objective lens..the lens has a rubber ring around the outer diameter between the front placeholder that needed a bit of fiddling to get right) but I'm planning on going through the routines I came across in this topic here, it's a bit involved but hey, what isn't in this hobby! I'd already started collecting some data on the veil nebula and didn't want to disturb the image train until that's complete. Honestly I'd probably be happy leaving it well enough alone at this point as the problem is mainly in one corner but I would like to do some mosaics in the future so...

Either way, I guess at some point you have to throw in the towel and just try and enjoy what clear skies you have, plenty of rainy nights to bang your head over the rest

Edited September 26, 2022 by Sien

[WolfieGlos]

Hi Sien. Glad you managed to get a better result than me, usually I’m quite a patient person but not on this it seems! 

That’s at interesting topic you’ve linked there, quickly skimming it, it looks promising.

Interesting you say about mosaics, that’s not something I’m considering for a while yet, but if the stars are in 1 corner only, could you just keep the eggy stars on an area of overlap? 

I didn’t get to test that device from FLO even though it arrived in time. I’m now away down under for 3 weeks, hoping I can catch the Milky Way whilst here, but keep us updated if you try the tilt adjuster or Astrobin guide 😊

[carastro]

I'm really confused here.  Isn't the Skywatcher ED72 a refractor, I just bought one.  Why do you need to collimate it?  Newtonian's need collimation.  

However if you are referring to the tilt one gets tightening up the 2 bolts to clamp on the camera that's a differeent issue.

I bought the Skywatcher ED72 to replace my William Optics ZS71 which i have had for a few years as I was never able to eliminate focusser tilt due to there being no thread on the draw tube on which to attach a Baader click lock (this squeezes the camera and Flattener/focal reducer in place and thus avoids tilt).  This works well on my other telescopes, and I wanted to be able to do so with my smaller scope.

I bought an M54 Baader click lock which fits this scope.  Check it out with FLO.

If I have misunderstood this thread please excuse me.

Carole 

 

Edited October 4, 2022 by carastro

[StevieDvd]

@carastro though not in the same way as a reflector, a refractor is collimated (mainly at factory and less often by the end user) than needed with a reflector.

It comes in 2 stages - the fitting of the focuser (being tilted) and the cell assembly of the objective. Some objectives have collimation screws/locking screws, others have spacer rings.

That being said the number of refractors needing collimation are few and mainly due to the focuser (or someone taking the object apart to clean).  You don't tend to hear of many people needing to collimate even when they replace the focuser with a more up market one - some of which have collimation adjustment.

See https://www.opticalvision.co.uk/documents/202.pdf for adjusting one.

 

[Sien]

What Stevie said. I'd wager a few of us are just unlucky in the QC department or the handling of the scope in its travels to your door.

I checked mine again today and it was a fair bit out of whack checking with a cheshire, there's almost no room to maneuver between the focuser and the objective lens which leads me to believe the focuser assembly attached to the scope isn't entirely level (I think it might actually need a shim or grinding down the surface to tilt it the way it needs to be). Get what you pay for I suppose? I got it as close as I could but it took a LOT of back and forth, had to hold the front objective lens firmly in one corner and tighten it up while also trying to adjust the grub screws around the focuser. It's difficult to keep the lens where it needs to be because there's a rubber spacer between the outer ring and it just wants to grab the lens and spin as you are trying to tighten it. When you get it where it needs to be, I'd say it wouldn't hurt to apply some thread locker so it doesn't move with future bumps and such.

Afaik, you'd use a laser to square your focuser, and a cheshire to collimate the lens from there.

 I've had fun with this scope but, think I'll be upgrading in the near future.

This was my first refractor, but I spose I learned a lot, whether I wanted to or not I would have returned the scope but as a beginner I knew none of this until I was out of warranty.

Edited October 7, 2022 by Sien

[alacant]

On 07/10/2022 at 23:34, Sien said:

the QC department

Hi

We've yet to see a 72ed emerge from its tissue paper correctly aligned. Apart from the infamous impossible-to-adjust grub screws on the focuser collar and the rubber washers in the focuser, another popular cause of misalignment is the lens itself which is jammed into the end of the tube at an angle and tightened to death at the factory. Or conversely, loose and not threaded home.

The latter can easily be rectified by loosening the slotted retaining collar until the lenses rattles upon agitation of the tube. This allows the lenses to re-seat. Then, keeping the tube vertical, gently tighten the collar until the rattle just disappears. Finally, remove the lens cell (it unscrews) and clean any swarf or plastic bits which would otherwise prevent the cell from seating correctly.

Now go back and realign the focuser. You'll probably find that it will be back to its original position. 

Cheers and HTH

Edited October 9, 2022 by alacant
ortografía - spell

[Sien]

Thanks for your advice, will take it on board next time I have my rig stripped down.

[Turbocoo]

Been having a nightmare with my 72ed too. top left and right of subs have eggy stars bottom left and right are fine. Originally had an OVL FF but i wasnt impressed so bought a Stellamira , things started to improve at 66mm spacing.

When my scope arrived collimation was out by 7mm!! Having adjusted the focuser to tube alignment, with those awful grub screws, I really cant tell where tilt issues are coming from. Three different dslrs all tell the same story.

As far as main lens cell is concerned my dew shield cannot be removed, when i try twisting it off, the entire lens cell starts to unscrew and its a newer version of the scope!

The scope was bought new from Camarthen Cameras at the start of August, I'm very tempted to return it. I've wasted very few precious clear skies( North coast Northern ireland For goodness sake), trying to sort this out.

Should have went for a WO 73 or similar

[Turbocoo]

On 09/10/2022 at 13:19, alacant said:

Hi

We've yet to see a 72ed emerge from its tissue paper correctly aligned. Apart from the infamous impossible-to-adjust grub screws on the focuser collar and the rubber washers in the focuser, another popular cause of misalignment is the lens itself which is jammed into the end of the tube at an angle and tightened to death at the factory. Or conversely, loose and not threaded home.

The latter can easily be rectified by loosening the slotted retaining collar until the lenses rattles upon agitation of the tube. This allows the lenses to re-seat. Then, keeping the tube vertical, gently tighten the collar until the rattle just disappears. Finally, remove the lens cell (it unscrews) and clean any swarf or plastic bits which would otherwise prevent the cell from seating correctly.

Now go back and realign the focuser. You'll probably find that it will be back to its original position. 

Cheers and HTH

"another popular cause of misalignment is the lens itself which is jammed into the end of the tube at an angle"

I wonder if this is my problem? See previous post.

Thanks

[AstroNebulee]

1 hour ago, Turbocoo said:

Been having a nightmare with my 72ed too. top left and right of subs have eggy stars bottom left and right are fine. Originally had an OVL FF but i wasnt impressed so bought a Stellamira , things started to improve at 66mm spacing.

When my scope arrived collimation was out by 7mm!! Having adjusted the focuser to tube alignment, with those awful grub screws, I really cant tell where tilt issues are coming from. Three different dslrs all tell the same story.

As far as main lens cell is concerned my dew shield cannot be removed, when i try twisting it off, the entire lens cell starts to unscrew and its a newer version of the scope!

The scope was bought new from Camarthen Cameras at the start of August, I'm very tempted to return it. I've wasted very few precious clear skies( North coast Northern ireland For goodness sake), trying to sort this out.

Should have went for a WO 73 or similar

I'd send it back to the retailer and get them to sort it, save you the hassle of it. The dew sheild will come off if you turn it the other way and pull it off as its quite tight and helped hold in place by a thicker felt strip. 

Lee

[alacant]

4 hours ago, Turbocoo said:

I wonder if this is my problem?

We only realised after the hassle of the brushed aluminium collar and focuser alignment. It takes only 5 minutes to set the lens square, so almost certainly worth a try.  BUT: bear in mind, any adjustment you did at the focuser end will almost certainly have to be undone. We found on the two examples we had  that setting the collar back to it's original position was all which was needed. If you didn't remove the flexible rubber in the focuser on your first attempt, now is the time to do it.

Cheers and HTH

[alacant]

5 hours ago, Turbocoo said:

dew shield cannot be removed

it's not threaded. Hair-drier for a few moments around its base, then wobble and pull rather than unscrew.

You're going to remove the lens cell anyway but its easier to remove the lens shield with the cell still attached.

HTH

[Turbocoo]

1 hour ago, alacant said:

it's not threaded. Hair-drier for a few moments around its base, then wobble and pull rather than unscrew.

You're going to remove the lens cell anyway but its easier to remove the lens shield with the cell still attached.

HTH

Sorry to appear a bit dopey but are you referring to the rubber washers in the focuser as they are still intact. 

Secondly you say that the lens cell is "jammed into the end of the tube" but surely it is threaded on and I can't see any way to adjust for cell being jammed in at an angle. 

Thanks for your help and quick replies 

Bryan 

[Turbocoo]

Well, look what we have here. The dew shield screws off with effort and heat from a dew band. 

Thought most of these scopes did not have a threaded shield 

[alacant]

1 hour ago, Turbocoo said:

jammed into the end of the tube

Sorry. English is not my native language. Whatever it means it is that the cell is not sitting square to the tube (dirt/poor threads/swarf) and/or the lenses themselves have not been allowed to seat parallel to each other before being tightened. Usually just loosening and retightening everything GENTLY is all that is needed.

1 hour ago, Turbocoo said:

rubber washers in the focuser

Yes.

51 minutes ago, Turbocoo said:

did not have a threaded shield 

All the ones we've seen have been push fit. Well done for persevering. 

[AstroNebulee]

1 hour ago, Turbocoo said:

Well, look what we have here. The dew shield screws off with effort and heat from a dew band. 

Thought most of these scopes did not have a threaded shield 

Ahh I see. Sorry mine is the older 'longer' tube version when regarding the dew sheild. 

Lee

[WolfieGlos]

On 07/10/2022 at 22:34, Sien said:

What Stevie said. I'd wager a few of us are just unlucky in the QC department or the handling of the scope in its travels to your door.

I checked mine again today and it was a fair bit out of whack checking with a cheshire, there's almost no room to maneuver between the focuser and the objective lens which leads me to believe the focuser assembly attached to the scope isn't entirely level (I think it might actually need a shim or grinding down the surface to tilt it the way it needs to be). Get what you pay for I suppose? I got it as close as I could but it took a LOT of back and forth, had to hold the front objective lens firmly in one corner and tighten it up while also trying to adjust the grub screws around the focuser. It's difficult to keep the lens where it needs to be because there's a rubber spacer between the outer ring and it just wants to grab the lens and spin as you are trying to tighten it. When you get it where it needs to be, I'd say it wouldn't hurt to apply some thread locker so it doesn't move with future bumps and such.

Afaik, you'd use a laser to square your focuser, and a cheshire to collimate the lens from there.

 I've had fun with this scope but, think I'll be upgrading in the near future.

This was my first refractor, but I spose I learned a lot, whether I wanted to or not I would have returned the scope but as a beginner I knew none of this until I was out of warranty.

Well, I'm back and the weather here in the UK is beyond terrible. I ordered the Astrodymium tilt adjuster before I left, I had 1 shot on Friday, which I tried without the adjuster and got 21% tilt. After that single frame, it clouded over....and rained. So then Saturday, as it was clear despite the forecast saying otherwise, I decided to just have 1 go with the rotater, and see what happens. Wasn't even fussy about where the raised edge would be.

I added the 0.2mm thickness adjuster between a 5mm spacer and my T-ring, aimed at the same target as the night before......and I got 5% tilt on a test shot. As it was clear, I decided to stick with it (Ring Nebula, so a massive crop on the image anyway)..... and I got varying results of between 5-10% tilt during a 1 hour session...so massively improved! That put's me at circa 60mm backspacing.

Next time we get a break in the clouds, I will keep the same camera angle/rotation but try different targets to rotate the scope a bit more and see what it gives me. I'm tempted to refine it, but on the other hand...I'm also tempted to stick with it !!!!

[gaz81]

Been having the same issues with my 72ED

Also did the paper target on the end and fired a laser collimator through it. I had to adjust the focuser seating as it was way off. 
 

Always important to collimate the collimator first though! 

[Adam J]

On 10/05/2022 at 15:36, AstroMuni said:

Hi Sien,

Collimation with a Cheshire is usually done for a Reflector. The 72ED sounds like a refractor. Have I misunderstood something?

No you can colimate refactors with a Cheshire too by shining a light source down the Cheshire reflector with the lens cap in place you will see reflections from each lens surface that should be concentric if colimated correctly. 

You do need a lens cell that has colimation screws though. Not all the cheaper refactors do.

Reading further down this thread I see several procedures that I really do not recommend the OP undertake, moving the lens cell as a whole is one thing messing about with lens element alignment is a one way ticket to hell. Undoing the lens retaining ring.....really bad idea. De-centred lens elements on an APO leads to lateral chromatic aberration. 

I also see that the Cheshire method was explained. 

All in all this scope should have been returned and exchanged for a new scope. 

Adam 

Edited November 7, 2022 by Adam J