29 replies to this topic

[J^2B]

Hey Everyone,

 

Last summer I took the Criterion 6000 out and looked at Saturn and found some flaring and I couldn’t get Jupiter or Mars to resolve (I think I was looking at Mars) so I thought it needed collimation. Last night I took the tele out, polar aligned, tested the drive motor and all seemed good. I then set Aldebaran on tracking, defocused on lowest power and noticed the secondary shadow was slightly off center. I thought I’d try my first ever attempt at collimating and just made things worse . . . way worse.

 

Things that happened . . .

 

1) I tried following the manual by putting the star on the edge of the FOV in the direction of the shadow and adjusting the screw opposite that direction by fractions of a turn. Unfortunately, the way the shadow was and the way the screws/housing were oriented there was no exact opposite screw so I started adjusting the one nearest.

 

2) Upon adjusting the secondary screws the secondary housing slipped under the torque and rotated clockwise. I twisted a little more until it tightened to a stop.

 

3) Things got worse. The defocused star moved around the FOV so I tried compensating, but then the circle halo became oblong/elliptical shaped. I tried getting the egg back to a circle and the shadow centered but then the halo went from egg-shaped to like a delta (or semicircle) shape.

 

4) I got it back into an eggish shape with the shadow a little off center, but then clouds rolled in.

 

5) I fought through the clouds and the sky cleared up but my further attempts proved futile and the halo is now kind of like a gumdrop shape with the shadow a little off center to the top.

 

I am wondering if when the housing slipped it cause the halo to take on different forms.

I fear that by adjusting the screws so much I have damaged the corrector lens

I fear I have placed the things so out of alignment it will take a telescope repair person to fix it (which I have yet to find in my area).

I have literally working myself into nausea thinking about how bad I messed up and if it can’t be fixed.

In hindsight I feel like the telescope was never out of collimation but my wanting everything to be perfect and perfectly centered has caused significant harm

Can someone please tell me that everything is going to be okay and help me get my telescope healthy again?

 

Best Regards,

 

Jesse

 

What the FOV roughly looks like (see attached - hope the attachment works)

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Edited by J^2B, 26 December 2018 - 06:43 PM.

[DAVIDG]

  Unless you cracked the corrector you didn't damage it. Unfortunately the corrector is most likely poorly figured but that is another sorry.

   Do the collimation in your house were your comfortable and easily able to see what is going on. Take a flashlight and cover it with tin foil and make a pin hole in the foil to make an artificial star  Now place it as far away from the scope as possible, like one end of your basement. 

   Put the eyepiece directly in the scope so no star diagonal. Aim the scope at the flash light and center the artificial star and defocus it about 1/8 turn.  So the way my secondary cell on my DX-8 works is there Push and Pull screw pairs. So if you tighten a pusher you need to loosen the puller.  So pick a set of screws and make an adjustment. After each adjustment center the artificial center. If it get worse then you do the opposite. If you take your time it should take more then  about 15 minutes to get  it back to being aligned. Once it looks perfect it should only take a minor tweak on a  real star to get it perfect.

   Just a word of caution, if your optics are like what I have seen when testing many DX-8, 6 and 4, you may not be able to get round stars because the optics are just very poorly figured and the flares your saw are optical defects and not miss alignment. Good luck.

 

                            - Dave 

[davidc135]

It may help initially to remove the ep, and diagonal if you have one, and point the scope at a light surface. Using the baffle as a guide to centre your eye a reflected image of the corrector will be seen in the secondary. The three pull screws (if it's the same as my earlier DX-6) enable the secondary mirror with it's backing aluminium disc to swivel about a ball bearing. Slacken one (or two) screws before tightening the opposing one until the image is roughly centered, then follow Dave's advice above.

 

David

Edited by davidc135, 26 December 2018 - 09:58 PM.

[DreamWeaver]

My 6000 uses a ball bearing like David's DX-6 for the secondary pivot. Hopefully your 6000 just needs to be collimated.

You might want to check that your secondary is centered on the corrector plate. I used a laser collimation tool and some printed targets to check the alignment of the primary baffle, the hole in the corrector, and the secondary secondary holder. I remounted the secondary on its mounting plate because it wasn't centered. Unlike my Meade and Celestron SCTs, the 6000 has a very rough edge on the outer edge of the corrector. The only way I could center the center hole in it was to have the edge of the corrector touching the side of the tube. DavidG, is there a safe way to smooth the edge without risking damage to the corrector? 

After all all those steps, I now see nice round stars with round defraction rings.

The first image below is from my C8, but will give you an idea of how I used the laser to check alignments. The second is one of Jupiter taken with my 6000.

 

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[J^2B]

Thank you all for your wisdom. Unfortunately I don't have a laser collimation tool although I think I might need to get one if the secondary is misaligned to the tube in the primary (the baffle?). When I de-focused Aldebaran the first time the halo (both inner and outer radii) looked great in terms of circularity. It's just the shadow of the secondary was just slightly off. I will try the tinfoil flashlight approach tonight with a distance of about 30ft (I have a small house with no basement). 

 

If i understand it correctly I want to put my eye in the rear back, look down the tube (again baffle is what it's called?) and look for my eyeball on the secondary mirror? and also look for the reflection of the corrector in that mirror? I fear I worked the allen head screws so much there is some slop where the wrench fits in. I will also make note to loosen *two* and tighten *one.* I think last night I tightened one then loosened another or loosened one and tightened another, then tried the two/one approach. It got so late i thought it best to pack it up and ask you fine people.

 

Best Regards,

 

Jesse

Edited by J^2B, 26 December 2018 - 11:41 PM.

[davidc135]

Just for completeness I'll mention that the secondary housing has a cover plate that must be removed to reveal the real collimation screws. But as you mention Allen head screws and not slot heads you must have realized this.

The two parts of the secondary housing screw into each other and (lightly) hold the corrector plate. Overtightening the collimation screws won't in itself affect the plate but it's possible that overtightening the whole secondary assembly may have pinched the optics. If it's possible to unscrew and then lightly tighten the secondary housing without removing the corrector it could be worth it.

 

Yes, it's the primary baffle that you look through and, as you say, your eye can be seen within the image of the secondary and corrector plate that have themselves reflected first off the primary and then off the secondary en route. If collimation is very off you'll also see the side of the tube.

 

David

[davidc135]

There may be a limit to what collimation can do for Criterion DXs and 6000s. Their  correctors have a poor reputation although maybe the 6000s are better. Here's a single pass Foucault pic of my DX-6, not well aligned. The rough wavefront is out by a wave or more although it worked well up to x60 or so and perhaps could image reasonably(?) 

 

David

 

P.S Dreamweaver's 6000 does seem to be a lot better with it's Airy disc and rings at focus

Edited by davidc135, 27 December 2018 - 02:55 PM.

[DAVIDG]

"DavidG, is there a safe way to smooth the edge without risking damage to the corrector?"

   If your corrector is like the 5 DX-8 ones I have, you'll see a scribe line around the edge that glass was marked too when it was cut out of the  sheet. 

   So all you need to do is to use a wet stone to grind the edge,  to the line,  to clean up the edge. Just run the corrector under a  light stream of water and grind the edge down to the  line to smooth it out. 

   I just went down to the basement and grabbed one of the correctors and ground down a rough section of the edge. It took maybe 5 minutes.  Your not going to distort the figure by grinding the edge.

   Here are couple of pictures showing the before and after. You can see the scribe line in the first picture.

 

                           Happy Holidays !

                             - Dave 

 

 

 

 

[DreamWeaver]

Awesome, thanks Dave!  My corrector does have the scribe line.  The edge is so rough though, there's no way to use spacers to keep it centered.

[davidc135]

Jesse

I've been working on my DX-6 and the rule seems to be to tighten a screw to push the reflection of the secondary in the opposite direction. (No diagonal).   David

[Gil V]

When looking straight through (no diagonal) think of it like “tighten the screw(s) where the coma is flared”.

You “pull” the airy disk back to the center.

Use a 6mm eyepiece for final collimation.

[J^2B]

Thanks everyone! I truly appreciate the feedback.

 

So far I have tried DavidG's pinhole flashlight approach and it has helped alot! I looked down the baffle and saw my eye staring back at me. I rotated my head in a circle (looking around the corrector) and saw no apparent damage. I hope the allen screws are, in fact, the collimating screws because those are the one's I adjusted (I took off no cover plate (if there is one)).The airy disk seems to be about back to where is was originally. The rested and reassured self along with the comfort of being inside and having a non-moving subject helped tremendously. The pinhole light seems to focus back to a nice sharp point. Now I'll need to take it outside and fine tune it with a real star. Assuming the scope has never been collimated I am worried that my monkeying around made the assembly now more prone to becoming misaligned. I am still not sure if the secondary is out of alignment with the primary. I mean i saw my eyeball and not the side of the tube so that is good, but what if it is out of alignment and not noticeable to me, but is noticeable to the optics?

 

I wish I could take the scope apart, clean it and align everything, but I have neither the space, nor the money for tools or a new scope heaven forbid something goes terribly wrong.

 

On a side concern, I am using the Golden Pyramid and have a somewhat rough time polar aligning the scope. Granted, it was my first time and didn't take too terribly long, but also wasn't very precise (precise enough by my standards) for astrophotography. The tripod doesn't have a Declination degree scale so I roughly sighted Polaris through the wedge, attached the scope, sighted Polaris in the finder by many iterations of unscrewing the knobs and adjusting. I found it with the 30mm and turned the clock drive on. Moved to Aldebaran and the scope kept it in view (thanks goodness!). I am not sure about any drift that may have occurred but the relative position stayed about the same. I am looking for polar scope options online, but the one's I am finding say they work for telescopes x. y and z (none of which are mine, ofcourse, considering its age and no longer manufactured). 

 

Also, I noticed that when tilted on the tripod and spun in RA that about a 1/4 of the rotation seemed rough or sticky. Perhaps due to imbalance? Although there was no camera on the scope. I am concerned that when I do hook up a camera that will cause tracking problems. I would like to grease the RA gears and DEC components but that would involve taking it apart. 

 

Finally (for now lol - sorry for being such a windbag) I thought i remember seeing an autoguider port (telephone style input) but must be mistaken. So to precisely guide I must get some kind of drive corrector and an off-axis guider. The manual says to adjust via the drive corrector and the DEC knob, but realized to myself the other night that adjusting the DEC knob vibrates the scope making a clean; streak free image seem impossible. Any thoughts or ideas?

 

Thanks for Reading,

 

Jesse

Edited by J^2B, 28 December 2018 - 07:25 PM.

[DreamWeaver]

Glad to hear that you were able to get the collimation back. Now you just need a night of great seeing to fine tune it on Polaris.

 

What camera will you be using for astrophography? Depending on the camera, you can still achieve good results without guiding. The image below was taken through my Meade 8" LX3, using an older Canon 450D (XSi) without guiding. By just doing a drift alignment on the telescope, I was able to take two minute exposures. This image is a combination of 15, 30, and 120 second captures.

 

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[J^2B]

Hey Dream,

 

Great pic! I was briefly reading about drift alignment and might actually have to sit down one day and dedicate more brain power to figuring it out. If that is the only feasible and sure fired way then that it shall be. I will be using an 11-12 year old Nikon D700 12MP Full frame. It's all I got, but I don't even know that I'd trade her out even with the low MP. Luckily, last night was clear and cold (though I passed out read about drift alignment lol while letting the scope reach thermal equilibrium). I woke up at 01:15 and seriously contemplated setting her up and checking collimation on a real star, but decided on sleep. Tonight should be as clear and cold as last night so I hope to stay awake.

[DreamWeaver]

Thanks Jesse!  Your Nikon will be fine.  The Canon 450D is 12.2MP.  The part I like about drift alignment is that it's free!    Even if you could auto guide the 6000, you would want to drift align it first, so the autoguider doesn't have to work as hard.

 

I want to try some imaging with the 6000 one of these nights.  I must be getting old though.  I survived growing up in Minnesota, but now these Arizona nights seem cold.  

[J^2B]

lol you know it Keith! I must be getting old too then. I have a $100 dollar credit at Celestron and I am weighing my options, but considering the autoguider is out of the running I think I am going to get the Observer's Accessory Kit ($110) that comes with two "high quality" Plossl eyepieces, T-adapter+2x barlow, three filters, cleaning cloth and hard case). I believe the T-adapter is prime focus, however in the manual they show a different adapter and specify achieving cassegrain focus. Not exactly sure what the difference is though. All I know is that I need a T-adapter because right now the only way to take photos with my camera is with a 24-120mm lens and that just ain't cutting it. Hopefully in the near future i'll get a tele-extender, counterweight set and a remote shutter release. I can't wait to start taking pictures like yours! Did you take three subs or was that Xx15s, Yx30s, Zx120s?

Edited by J^2B, 29 December 2018 - 12:04 AM.

[DreamWeaver]

It was taken around 3-4 years ago.  I think it was something like 10x15, 10x30, and 20x120, along with darks and flats.

[Gil V]

Jesse - the sticking in RA when the mount is loaded concerns me.


Pop the cover off the top of the mount base, get a NEW allen wrench, and give that hidden screw a solid tightening.

Edited by Gil V, 29 December 2018 - 01:30 PM.

[J^2B]

Thanks Gil, the telescope is sitting on the counter and last night I spun it around in RA slowly and could definitely feel an arc with some resistance. Can you help guide me through the process of popping the cover off? 

 

Also does anyone have any tips or tricks to drift align the telescope that is on an old original wedge? The wedge uses four knobs that are positioned horizontally and i have to loosen two (or four or a combination) of them to man-handle the telescope until it roughly aligns. From what I've been reading/seeing after I have roughly aligned to Polaris I am supposed to find an eastern star and southern star and drift align them (independently). However, man-handling the wedge in DEC probably won't provide the slightest of corrections that I will need to perform.

 

One more thing  , what do you guys think of the Celestron Universal 2x Barlow with T-Adapter (image attached)? In one Celestron model description it says it's for a refractor (which I can see how it was designed that way), in another model description it just says the telescope, and in the Astronomics description it says it can be used in the visual back of an SCT but be careful as the camera is only held in by a screw. I have yet to find a Barlow + T-Adapter that is designed like the prime focus adapter in that it screws into the visual back. If there isn't one and I have to get the one shown I am tempted to find a metal worker and have them build a 2-in-1 counter-weight bar + camera platform. I figure the added camera platform will serve two purposes. 1) help support the load to help prevent/minimize t-adapter tube or projection tube flex and 2) hold the camera in place so it won't have the chance to potentially fall off.

 

As always thank you for reading and commenting 

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Edited by J^2B, 03 January 2019 - 05:39 PM.

[J^2B]

Hey Gil,

 

Were you talking about this cover and screw? 

 

Also do you see any issues with me applying a small amount of grease to the DEC threaded rod where the adjuster sits to hopefully make the action more smooth and effortless?

 

 

Thanks,

 

Jesse

Edited by J^2B, 08 January 2019 - 07:10 PM.

[DreamWeaver]

I wonder if a previous owner of your scope changed the screw, or if Criterion just used whatever type they had lying around.     Mine is a different style screw.

 

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[J^2B]

Lol! Yours looks like a build when the parts were still flowing in and business was good, mine not so much. And yours is all clean and mine is showing rust and age /sigh. Anywho, not sure if that is supposed to be the hidden allen screw. That was the only thing that looked poppable.

Edited by J^2B, 09 January 2019 - 11:53 PM.

[DreamWeaver]

They used the same masking tape on both of ours.     Mine was stuck under the cap.

 

I wonder if Gil was thinking of the Dynamax.  Maybe they used an Allen head screw.  The screw in your picture is the one he's referring to.

[J^2B]

Thanks Keith. I might be tempted to replace the screw or just forget about it and tighten it down. Wondering if there is something i should do about the decrepit state or just leave it. I do want to follow the manuals advice and clean the outside of the OTA, fork and base with 409. I noticed some specs on the secondary that i want to clean off (thinking a modified air blower + vacuum that i can slide up the baffle). Would you recommend the Celestron Pro wedge? I think i need something with fine tune adjustment for when i try drift aligning it. Currently i have the OEM golden tripod + wedge.

[DreamWeaver]

The Celestron Pro wedge should work.  The mounting holes are different, so you'll have to mount it with just the one top bolt.  That's what I do when I use the 6000 on my old Meade LX wedge.  It feels secure enough, but I wouldn't carry it outside with it attached to the wedge with just one bolt.