Mirror Lock on Edge HD8 - Forums

Topic starter

Frequent contributor

Nov 20, 2023

When I am using the ZWO EAF with the Edge HD 8", I am assuming I should not lock the primary mirror if I automate focusing.
But if the temperature differential between when I start imaging and when I end imaging isn't large, I assume I can keep the mirror locked and, if I need to re-focus, say, after a meridian flip, I can unlock the mirror focus and then re-lock it.

Does this sound like a good plan?

Thanks,
Jerry

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Miguel A.

Nov 20, 2023

Hello, Jerry. When I use my CEHD8 with the ZWO EAF, my primary mirror (in the rear) is unlocked. The only time I lock it is during travel/transporting.

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James

Nov 20, 2023

I don't use the mirror locks either, since I have the celestron focus motor installed on mine.

If you were to install an auxiliary/crayford focuser, and use that for autofocus instead of the original focuser, then you would use the mirror locks.

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Farzad

Nov 20, 2023

Jerry Gerber:
When I am using the ZWO EAF with the Edge HD 8", I am assuming I should not lock the primary mirror if I automate focusing.
But if the temperature differential between when I start imaging and when I end imaging isn't large, I assume I can keep the mirror locked and, if I need to re-focus, say, after a meridian flip, I can unlock the mirror focus and then re-lock it.

Does this sound like a good plan?

Thanks,
Jerry

The locking mechanism is expected to be used when the scope is in transportation. When in use, regardless of focusing method, the mirror should be unlocked. This is according to Celestron.

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Lasse Skov

Nov 20, 2023

I keep the mirror locks unlocked at all times on my EdgeHD 9.25 using the Celestron EAF.

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Jeffery Richards

Nov 20, 2023

Farzad:
Jerry Gerber:
When I am using the ZWO EAF with the Edge HD 8", I am assuming I should not lock the primary mirror if I automate focusing.
But if the temperature differential between when I start imaging and when I end imaging isn't large, I assume I can keep the mirror locked and, if I need to re-focus, say, after a meridian flip, I can unlock the mirror focus and then re-lock it.

Does this sound like a good plan?

Thanks,
Jerry

The locking mechanism is expected to be used when the scope is in transportation. When in use, regardless of focusing method, the mirror should be unlocked. This is according to Celestron.

This is inaccurate for an Edge HD scope. The mirror locks were added as a means to minimize/eliminate mirror flop during use for imaging (one of the biggest issues with moving primary mirror type scopes).

Your plan to lock the mirror and then only unlock it if necessary due to focus shift is reasonable and will help with minimizing mirror/image shift during exposures. The better option is to gross focus with the primary and lock it down and then use another final/adjustment focusing method (rear cell in-line focuser like a crayford type or if money is no object then the Optec secondary focuser).

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Björn Arnold

Nov 20, 2023

Farzad:
The locking mechanism is expected to be used when the scope is in transportation. When in use, regardless of focusing method, the mirror should be unlocked. This is according to Celestron.

No, that's not the case: https://www.celestron.com/blogs/knowledgebase/how-do-my-edgehd-mirror-support-knob-flexible-tension-clutches-work-will-they-interfere-with-focusing-my-scope
The 14 inch scope has actual mirror locks to lock the mirror for transportation. The other scopes have mirror clutches.

Björn

Björn Arnold

Nov 20, 2023

Jerry Gerber:
When I am using the ZWO EAF with the Edge HD 8", I am assuming I should not lock the primary mirror if I automate focusing.
But if the temperature differential between when I start imaging and when I end imaging isn't large, I assume I can keep the mirror locked and, if I need to re-focus, say, after a meridian flip, I can unlock the mirror focus and then re-lock it.

Does this sound like a good plan?

Thanks,
Jerry

If you run a focuser attached to the main focus knob, I would keep the clutches open and let the software decide when an autorun is necessary. Certainly after meridian flip but also after a certain temperature change, HFR change or time. The temperature drop isn't the only possible cause of trouble. Already mirror flop can kick you out of focus.

Björn

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Jeffery Richards

Nov 20, 2023

Farzad:
The locking mechanism is expected to be used when the scope is in transportation. When in use, regardless of focusing method, the mirror should be unlocked. This is according to Celestron.

No, that's not the case: https://www.celestron.com/blogs/knowledgebase/how-do-my-edgehd-mirror-support-knob-flexible-tension-clutches-work-will-they-interfere-with-focusing-my-scope
The 14 inch scope has actual mirror locks to lock the mirror for transportation. The other scopes have mirror clutches.

Björn

To clarify, the C14 also has the flexible "locks" in addition to the actual mirror locks for transport.

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Jeffery Richards

Nov 20, 2023

Jerry Gerber:
When I am using the ZWO EAF with the Edge HD 8", I am assuming I should not lock the primary mirror if I automate focusing.
But if the temperature differential between when I start imaging and when I end imaging isn't large, I assume I can keep the mirror locked and, if I need to re-focus, say, after a meridian flip, I can unlock the mirror focus and then re-lock it.

Does this sound like a good plan?

Thanks,
Jerry

If you run a focuser attached to the main focus knob, I would keep the clutches open and let the software decide when an autorun is necessary. Certainly after meridian flip but also after a certain temperature change, HFR change or time. The temperature drop isn't the only possible cause of trouble. Already mirror flop can kick you out of focus.

Björn

I would add that if using the primary in an automated focusing arrangement the software should be set up to always final focus in the counterclockwise direction to ensure mirror loading against gravity which will help to minimize flop/shift.

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Glen M

Nov 20, 2023 · Edited: Nov 20, 2023

Farzad:
The locking mechanism is expected to be used when the scope is in transportation. When in use, regardless of focusing method, the mirror should be unlocked. This is according to Celestron.

From the Celestron manual and information available that I've seen, the primary function of the mirror locks are "to help support and minimize lateral movement of the primary mirror during astrophotography." I see nothing referring to locks being intended only for transportation, although it makes sense that one would lock the mirror for transport.

Jerry Gerber:
When I am using the ZWO EAF with the Edge HD 8", I am assuming I should not lock the primary mirror if I automate focusing.
But if the temperature differential between when I start imaging and when I end imaging isn't large, I assume I can keep the mirror locked and, if I need to re-focus, say, after a meridian flip, I can unlock the mirror focus and then re-lock it.

Celestron warns that Although turning the focus knob should not damage the telescope while the locks are engaged, undue stress can be placed on the focus mechanisms causing excessive image shift while focusing. I don't use an auto focuser for the Edge, but if I did I would just leave the mirror locks disengaged for the duration of my imaging session unless I was not intending to automate my focus periods, which would more or less contradict the reason I use an auto focuser.

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Poochpa

Nov 20, 2023

Jerry Gerber:
When I am using the ZWO EAF with the Edge HD 8", I am assuming I should not lock the primary mirror if I automate focusing.
But if the temperature differential between when I start imaging and when I end imaging isn't large, I assume I can keep the mirror locked and, if I need to re-focus, say, after a meridian flip, I can unlock the mirror focus and then re-lock it.

Does this sound like a good plan?

Thanks,
Jerry

Jerry ,
When I first installed an EAF on my 8" Edge, I would engage the mirror lock clutches after running the autofocus. It didn't take long before I forgot to unlock the mirror before refocusing. I now leave the mirror clutches unlocked at all times. Doesn't seem to adversely affect focus. I refocus as needed based on HFD/FWHM and after doing a meridian flip.
Mike

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mlewis

Nov 20, 2023

I think the best option, which has been mentioned above, is to gross focus with the mirror, lock the focus locks, and then autofocus using a crayford style autofocuser on the back of the scope instead of the mirror focus knobs. Of course, since you are set up with the EAF using the knob, unless you want to re-engineer your setup, this 'best way' is not available to you. With the more limited backfocus of the Edge8 it can be harder to find a suitable autofocuser to use this way in any case.

So given your actual situation, I would personally not be very comfortable doing any autofocusing using the focus knob on the scope with the mirror locked. I think you will have to keep it unlocked and accept any possible 'mirror flop' issues that might arise with your approach.

ML

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Phillip Hahn

Nov 20, 2023

The mirror lock is helping when doing visual astronomy. If you have the lock engaged and use the EAF, they work against each other leading to bent shafts of the mirror lock mechanism. I would advice to avoid this!
Personally, I keep the mirror lock engaged only during transport and have big label to unlock it before plugging in the power of the EAF.

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Miguel A.

Nov 20, 2023

Phillip Hahn:
The mirror lock is helping when doing visual astronomy. If you have the lock engaged and use the EAF, they work against each other leading to bent shafts of the mirror lock mechanism. I would advice to avoid this!
Personally, I keep the mirror lock engaged only during transport and have big label to unlock it before plugging in the power of the EAF.

Good idea to use a label as a reminder to unlock the mirrors, Phillip.

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Jerry Gerber

Topic starter

Frequent contributor

Nov 20, 2023

Thanks all for sharing your experience with me. If I plan on autofocusing at all during the night I will either keep the mirror unlocked or, if I plan on not refocusing during the session, then lock them down. Seems pretty straightforward as so long as I don't forget to unlock them if I focus manually or automate the focusing..

fielderda

Nov 21, 2023

I too have an EDGE 8 with a Celstron AF unit. I always keep the mirror locks - unlocked.
In NINA, AF is activated by temperature, time and meridian flip. I've not had any issues ever.

junktrunk

May 11, 2024

I think the best option, which has been mentioned above, is to gross focus with the mirror, lock the focus locks, and then autofocus using a crayford style autofocuser on the back of the scope instead of the mirror focus knobs.

Sorry to resurrect an old thread but I just found this discussion while researching my own focus issues for my Edge 8 HD. Could you say more about what a "crayford style autofocuser" solution would look like here? Are you saying something that would have its optics that it also has mechanics and electronics to focus? Is there a specific product you would suggest? And where does it go in the optical path, just before the OAG prism somehow I guess?

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