Edge HD 8, I'm having trouble with Collimation

Hi and good day,

have you tried to follow this instructions?

https://s3.amazonaws.com/celestron-site-support-files/support_files/1247509962_edgehd91030inst.pdf

CS

Fritz

In the image you can see very pronounced coma as a result of decollimation.
You should handle the collimation screws carefully and not loosen them again and again. Because at some point the secondary mirror can fall inside the Edge HD. Tightening too tightly can cause asti. So you have to handle this with absolute sensitivity. In your case all screws are tight.
This means that the screws that you could turn cannot get any further in because the others are holding them. Therefore, you should loosen these other screws minimally. Not even a quarter of a turn, and that's so easy to say.

Therefore, you operate the screws in turn, you tend to tighten them. If it doesn't work on one side, loosen the others a little. Tightening is important. This way the FS stays in position and nothing can happen. The secondary mirror on Celestron probably sits on a pin around which it tilts. By carefully tightening one screw and loosening the other if necessary, the position remains in the center. As is the distance. The advantage of the Edge HD is that the coma is distributed almost evenly across the field. So re-centering the control star on the axis is not as important as with the normal SCT.
I would make a wrist strap for the screwdriver. SO that it doesn't fall onto the Schmidt plate.

You can research everything else on the web yourself. Instructions in which direction to adjust with which screw can also be found at various corners. Collimation control using the camera is a good thing.

In Firecapture you can use multiple recording media. This makes sense if you collimate in focus at high magnification (approx. 1000x). It works even better in Metaguide. If the first contact ring is interrupted or asymmetrical, then you will have to deal with coma later. However, the controller requires fast exposure times on an 80% saturated star. 100% not, because otherwise the first diffraction ring will not be visible (supersaturation). The measure is exciting for high-resolution planet or moon photos. And more for advanced users.

I bought the same, lucky mine is centered since I use em for pver one year. I am not so talenteted and will bring mine to my dealer in worse cas…sorry I can not help more

regards

Hi! From the description it seems you are doing things just fine. About the metalligned pattern is it homogeneous over the whole frame or are there some differences between the center of the image and the corners? Just double checking. Also how much do you defocus just a little bit to see the outer focused diffraction pattern or do you actually see the whole projection of the secondary and so on?

center ones look more in than some of the edge ones.

Hi, I suggest you to do collimation without reducer and remember that the back focus of C8 edge is 133.5mm ( search on Celestron web site this doc: edgehd_whitepaper_final.pdf ). After set the right distance of sensor you can defocus manually ( starting from the best focus on non saturated star  adjusted only with C8 manual knob ), then try to  adjust the bob-knobs.  After to do this re-set the best focus manually, lock the knobs of main mirror and then you can mount EAF to perform the focus from remote. But I don't know if the back focus with 0.7x reducer is the same of standard C8 Edge.
Bye Adriano

sorry but my reasoning refers to the assembly of EAF with external focuser. In this way I can adjust the optical train and the back focus in the best way and lock the mirror locking screws definitively to prevent the mirror from moving when adjusting the focus or when you move the telescope. In any case I have no experience using the reducer. When the main mirror moves the collimation changes which is why I use the fixed optical train with external focuser.

Jason Schella:
Just for clarity, here is the proper places to measure for backfocus on the 0.7x reducer. Camera focal plane is the sensor of whichever camera you are using.

Thank you. I showed that in my photo, but it might make more sense to someone with the exploded view. 
The slightly tricky part is realizing that the reducer face is inside the adapter when screwed together. 

I used a different adapter, about a dozen different options come with the reducer, but my total back focus is the correct (for reducer use) 105.3 mm.

I too seem to be fighting my EdgeHD8 scope here recently. Have you tried using a tri-bahtinov mask for it? Not just a normal bahtinov mask because it won't show the patterns needed with simple rotation. 

One thing I read about collimation in general is that the secondary shadow could be off center with the scope in good colimation. Supposedly that is why the out of focus(doughnut) method is to just get you to a rough state that other methods tune up. I spent about an hour two days ago using the tri-bahtinov mask to make sure everything was nicely centered.

I have my backspacing perfectly set at 105mm and still have abirritations at the corners. I believe its because I need to check either side of the 105mm spec like I have also read online. My optical train is .7 reducer, Celestron OAG, and ZWO 294mc pro.

Do you have a link to the mask you use? 
thank you.