Screen shots of my specific Edge HD 8 Collimation issue - Forums

Started new thread with more info and pix that are not in this post below:
Something's wrong with my Edge HD 8 - AstroBin
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Hi.

I'm struggling with Collimation on Edge 8HD. Have proper back focus (105mm with .7x reducer from Celestron, measuring with digital caliper from arrow to arrow in my photo here, right arrow is my camera's sensor, left is bottom face of reducer inside adapter, ).

Bought scope used, but I know it works, I used it optically to view full moon without reducer, was stunning, all the way to the edge.

Using ASIAR to control and view, 3-second continuous refresh, using Zwo EAF to focus. I zeroed out the collimation screws (Bob's Knobs), they're not too tight, not too loose.

At one end of focus (using Jupiter, all stars were under clouds) I got the big view here (Though stars looked about the same earlier). Later using Polaris, after turning focus far, I got the little bird-like stars here.

If it helps, ASIAIR is reporting my focal length around 1450, not 1422.

I know the basics of astro, been doing it a year, taken many nice photos with 488 mm refractor.

I've watched about 10 videos on Collimation on Edge 8, none answer this question.

What should I do differently when the clouds break?

Thank you.

Hi,

If I put the pieces of information together that you provide, it seems the problem isn’t collimation but something at the end of the scope.
Since you’re saying that you had a stunning view of the Moon, I would assume your collimation is not extremely bad. Otherwise, you’re Moon view would have been really bad.
In any case, I recommend doing collimation with the eyepiece and certainly no reducer. If your collimation is fine then, everything else happens in the optical train after the scope.
My current bet: your reducer is bad.

Björn

Hi,

My current bet: your reducer is bad.

Björn

Hmmm. It's brand new. Was on backorder. Though I have had brand new astro gear faulty. Had a Zwo filter wheel that was brand new and dead on arrival. It's being fixed by them now.

Reducer has no moving parts though.

Would being VERY out of focus one way, and then in the other direction (plus a bit out of collimation) maybe give the results I show?

I'll consider your suggestion if no one else has a solid suggestion, first I'd like to try things that don't involve breaking down my whole train and measuring to get it right with my camera with no reducer. It's a lot of messing around with this and that adapter. It's almost an IQ test. lol.

If I do try without the reducer, I'll try without the reducer but with the camera. My 59 year old eyes aren't sharp enough to visually do this.

When I received my EdgeHD800, its alignment was completely off. Jupiter had a significant halo.

It doesn’t have to be an IQ test if you work systematically through the system. First confirm that the OTA is fine. Do the collimation without additional components. If you do it with an eyepiece or camera is up to you. Try placing the eypiece or camera at the back working distance (BWD) of the Edge and check collimation and image quality with short exposures. You won’t need guiding for that purpose. Once the OTA is fine, attach the reducer (which I personally wouldn’t use bit that’s another story) and camera only. Of course, BWD has to be correct. Check image quality again. If it fails here, you know your reducer is causing issues.

Björn

When I received my EdgeHD800, its alignment was completely off. Jupiter had a significant halo.

It doesn’t have to be an IQ test if you work systematically through the system. First confirm that the OTA is fine. Do the collimation without additional components. If you do it with an eyepiece or camera is up to you. Try placing the eypiece or camera at the back working distance of the Edge and check collimation and image quality with short exposures. You won’t need guiding for that purpose. Once the OTA is fine, attach the reducer (which I personally wouldn’t use bit that’s another story) and camera only. Of course, BWD has to be correct. Check image quality again. If it fails here, you know your reducer is causing issues.

Björn

Thank you. Trying without reducer sounds like a good idea.

What's BDW? Google is not helping

BWD = back working distance. Sorry, should have introduced it properly. Will update my previous post.

Björn

BWD = back working distance. Sorry, should have introduced it properly. Will update my previous post.

Björn

Is that the same, for my purposes, as back focus distance?

Because I know I have that correct (105.3 mm total with reducer.)

And I can get to the correct one without the reducer (134.5 mm total without reducer)

"I've watched about 10 videos on Collimation on Edge 8, none answer this question."

You've watched 10 videos on how to collimate an edge SCT and none answered what question, how to collimate? Something had to happen when you tried to collimate following just one of those videos. You can't make adjustments to the secondary without something happening. So what happened when you made adjustments?

Also since you are using an auto focuser and an OAG, make sure to keep the mirror locks disengaged. In fact, are you making sure the mirror locks are disengaged when checking the collimation?

Michael W. Dean:
BWD = back working distance. Sorry, should have introduced it properly. Will update my previous post.

Björn

Is that the same, for my purposes, as back focus distance?

Because I know I have that correct (105.3 mm total with reducer.)

And I can get to the correct one without the reducer (134.5 mm total without reducer)

Yes, for the EdgeHD800 its 5,25“ (133,5mm).

Yes, for the EdgeHD800 its 5,25“ (133,5mm).

Is it harder to columnate without the reducer at 2x the focal length and F10? (I assume I should try anyway, just to eliminate the possibility that it's the reducer.)

Do you always use your scope at native, without the reducer?

I'm thinking of also taking off the EAF and just using the hand knob. Would be quicker to get into focus, and I'd be sure to not take it too far if using by hand.

The back focus is 105, ok. Try to exclude the OAG in the optical train by replacing it with simple extensions, always reaching 105 mm. If the result is the same it could be that the camera needs tilting so reassemble the OAG and try again by tilting the camera (if it can do it). A quicker test to see if the problem is the optical train is to take a photo of the zenith, in this way you eliminate the bending stress on the optical train. If it improves, it means that there is flexion and you need to "stiffen" the optical train (finding the weak link which could be a poorly turned extension). Also check in the reducer that the tightening ring of the incoming glass (left arrow) is tight enough to make the incoming light perpendicular to the glass. Unfortunately, many attempts must be made to understand the source of the problem. Assuming that the main optics are ok you are left to work on the optical train and make everything orthogonal.

genny:
The back focus is 105, ok. Try to exclude the OAG in the optical train by replacing it with simple extensions, always reaching 105 mm. If the result is the same it could be that the camera needs tilting so reassemble the OAG and try again by tilting the camera (if it can do it). A quicker test to see if the problem is the optical train is to take a photo of the zenith, in this way you eliminate the bending stress on the optical train. If it improves, it means that there is flexion and you need to "stiffen" the optical train (finding the weak link which could be a poorly turned extension). Also check in the reducer that the tightening ring of the incoming glass (left arrow) is tight enough to make the incoming light perpendicular to the glass. Unfortunately, many attempts must be made to understand the source of the problem. Assuming that the main optics are ok you are left to work on the optical train and make everything orthogonal.

Thank you. Removing the OAG and replacing with just tubes makes sense to try (keeping same back focus).

Did you see the two photos of screenshots I posted above? Do either of them look normal for during trying to columnate?

Do you think it's possible the OAG prism is just sticking too far into my optical train and messing up the image?

I don't think the OAG prism can affect it but try to remove it and take some photos to see if anything changes but I don't think that's the problem, you would have had other aberrations.

columnate = you mean "collimation"?
if those stars are at the edge of the sensor then changes of a few mm or tenths on the distance are needed. If they are in the center, then it is necessary to act on the optical axis of the optical train. which camera do you use? if your sensor is smaller than an APS-C, try moving it away a little, usually the back focus of the lenses is tested on the APS-C. If it is larger, it should be approached a little by making attempts. But first it's best to try to make sure if it flexes

I had similar issues. I would bet your reducer is not performing. I gave up with mine, never made it right, whatever backfocus would I set. So , please check/do the collimation on native focal length , just a plain scope. Once you make that right , then try reducer and play with backfocus (do not touch collimation screws) . If your reducer is OK, with the right backocus , you'll get pinpoint stars. If you can't get it with playing with backfocus (and eventual tilt ) adjustment, send reducer back or put it into a garbage bin .
You can do collimation with reducer only if you sure it works perfectly, otherwise you are having unsolvable problem trying to fix reducer problems with collimation

Stjepan Prugovečki:
I had similar issues. I would bet your reducer is not performing. I gave up with mine, never made it right, whatever backfocus would I set. So , please check/do the collimation on native focal length , just a plain scope. Once you make that right , then try reducer and play with backfocus (do not touch collimation screws) . If your reducer is OK, with the right backocus , you'll get pinpoint stars. If you can't get it with playing with backfocus (and eventual tilt ) adjustment, send reducer back or put it into a garbage bin .
You can do collimation with reducer only if you sure it works perfectly, otherwise you are having unsolvable problem trying to fix reducer problems with collimation

I removed the reducer. I started a new thread and posted the link at the top here. I think you were responding while I was doing that.
https://www.astrobin.com/forum/c/equipment-forums/celestron-edgehd-8/somethings-wrong-with-my-edge-hd-8/?page=1#post-128331

Michael W. Dean:
Hi,

My current bet: your reducer is bad.

Björn

Hmmm. It's brand new. Was on backorder. Though I have had brand new astro gear faulty. Had a Zwo filter wheel that was brand new and dead on arrival. It's being fixed by them now.

Reducer has no moving parts though.

Would being VERY out of focus one way, and then in the other direction (plus a bit out of collimation) maybe give the results I show?

I'll consider your suggestion if no one else has a solid suggestion, first I'd like to try things that don't involve breaking down my whole train and measuring to get it right with my camera with no reducer. It's a lot of messing around with this and that adapter. It's almost an IQ test. lol.

If I do try without the reducer, I'll try without the reducer but with the camera. My 59 year old eyes aren't sharp enough to visually do this.

Wow just saw the pictures. This is not a normal collimation issue, this is something else. Have you tried looking at tyhe moon or something after the addition of the bob's knobs? Could it be that they are not really in place just yet? Also maybe a silly quetsion, is your mirror locked or not? this could be teh result of extreme strain on the mirror if you try to focus with the mirror locked by the locking screw. other than that I am baffled haha

"I've watched about 10 videos on Collimation on Edge 8, none answer this question."

You've watched 10 videos on how to collimate an edge SCT and none answered what question, how to collimate? Something had to happen when you tried to collimate following just one of those videos. You can't make adjustments to the secondary without something happening. So what happened when you made adjustments?

Also since you are using an auto focuser and an OAG, make sure to keep the mirror locks disengaged. In fact, are you making sure the mirror locks are disengaged when checking the collimation?

exactly my doubt, could be huge strain on the mirro due to locks not disengaged

Michael W. Dean:
Hi,

My current bet: your reducer is bad.

Björn

Hmmm. It's brand new. Was on backorder. Though I have had brand new astro gear faulty. Had a Zwo filter wheel that was brand new and dead on arrival. It's being fixed by them now.

Reducer has no moving parts though.

Would being VERY out of focus one way, and then in the other direction (plus a bit out of collimation) maybe give the results I show?

I'll consider your suggestion if no one else has a solid suggestion, first I'd like to try things that don't involve breaking down my whole train and measuring to get it right with my camera with no reducer. It's a lot of messing around with this and that adapter. It's almost an IQ test. lol.

If I do try without the reducer, I'll try without the reducer but with the camera. My 59 year old eyes aren't sharp enough to visually do this.

Wow just saw the pictures. This is not a normal collimation issue, this is something else. Have you tried looking at tyhe moon or something after the addition of the bob's knobs? Could it be that they are not really in place just yet? Also maybe a silly quetsion, is your mirror locked or not? this could be teh result of extreme strain on the mirror if you try to focus with the mirror locked by the locking screw. other than that I am baffled haha

I don't know what locking the mirror means or how to check, but it certainly sounds like it would explain the fact that no matter what I do it changes nothing. You mean the secondary mirror, right? The primary I've loosened the two knobs that lock the focus. I can focus, I just can't collimate.

How do I check?

I plan to look at the Moon next time it's up with no clouds. Though someone said the Moon might still look OK with this issue, since it's so big and bright.
\

Found the problem. I'm so far out I had to open it and adjust the mirror while looking at it.

Will report results.

Do you need a measurement

Michael W. Dean:
Found the problem. I'm so far out I had to open it and adjust the mirror while looking at it.

Will report results.

By the way, got lost in the multiple posts but the official screw size is given on Celestron's website here:

https://www.celestron.com/blogs/knowledgebase/what-are-the-sizes-of-collimation-screws-on-current-production-celestron-optical-tubes

I found the right titanium hex socket from a french supplier. I hated the philipps screw supplied with the scope.

For an 8" edgeHD scope they are M3x0.5mm screws, 12mm long

Michael W. Dean:
Found the problem. I'm so far out I had to open it and adjust the mirror while looking at it.

Will report results.

...... the official screw size is given on Celestron's website here:

https://www.celestron.com/blogs/knowledgebase/what-are-the-sizes-of-collimation-screws-on-current-production-celestron-optical-tubes

I found the right titanium hex socket from a french supplier. I hated the philipps screw supplied with the scope.

For an 8" edgeHD scope they are M3x0.5mm screws, 12mm long

I found one that's not titanium but hard stainless steel, I think this would work. https://www.amazon.com/gp/product/B07KRRNDGC
I might end up painting the part that's not thread black though.

Michael W. Dean:
Michael W. Dean:
Found the problem. I'm so far out I had to open it and adjust the mirror while looking at it.

Will report results.

...... the official screw size is given on Celestron's website here:

https://www.celestron.com/blogs/knowledgebase/what-are-the-sizes-of-collimation-screws-on-current-production-celestron-optical-tubes

I found the right titanium hex socket from a french supplier. I hated the philipps screw supplied with the scope.

For an 8" edgeHD scope they are M3x0.5mm screws, 12mm long

I found one that's not titanium but hard stainless steel, I think this would work. https://www.amazon.com/gp/product/B07KRRNDGC

Check the type of steel to make sure It doesnt rust over a like time un vert humid conditions. But yeah

Dustin Gazz:
Do you need a measurement

Thank you but no. My back focus is 100 percent correct. Please read my edit on the start of the first post of this thread.

Michael W. Dean:
I found one that's not titanium but hard stainless steel, I think this would work. https://www.amazon.com/gp/product/B07KRRNDGC

Check the type of steel to make sure It doesnt rust over a like time un vert humid conditions. But yeah

stainless steel 304 (A2-70). Googled and says it does not corrode unless exposed to salt air. I'm 350 miles from an ocean so I'm good. I ordered 100 (for 9 dollars) so if they work and I start sending them out as gifts I'll only do with people far inland.