Mr floppy the C11 with flop

[ncjunk]

I have done too many changes to my system over the last six months and thought some bad tracking i was getting was due to the eq6 belt mod.

I was getting spikes of 20 pixels and also pointing in the dec would be out by 2 degrees and 35 arcminutes in the ra.

I found last night that pointing was great around a localised area but when i slewed south a large distance it jumped the 2degrees.

It's not the mount as i have reverted back to gears so no possibility of slipping belts.

So it's mirror movement possibily related to when i first got the mount and a screw was left in place which caught on the mirror whilst i tried to focus. It shifted the mirror out of alignment so i can only assume it loosened something as well.

What do i do as i like the scope but need movement of less than 4 arcminutes or automatic plate solvings a pain...

So:

1. Take apart the c11 and see if i can tighten up the mirror so it doesnt move as much.

2. Try locking the mirror down with some screws or something. (i have a crayford and focuser so just want the thing fixed in place)

3. Buy a 10" f4/5 newtonian instead and sell the c11.

I'm confused and really can't be bothered with opening up the c11 and dont really enjoy the hassle of selling stuff....back to the ed80 whilst i decide (sigh)

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[Merlin66]

Unless you've done some physical damage to the mirror support I'd recommend running the mirror through the full travel of the focuser - this spreads the grease along the baffle. This should be done regularly.

You can verify the possible mirror movement by imaging then reversing the focusing direction - any movement you see will be the maximum "flop" during fast slewing.

I have a C9.25 and a C11 and have to say the mirror slop/ flop is significantly less than the Lx200's I was using.

[Mr Spock]

I have a C9.25 which has very little flop - a tiny fraction of a 140 Mak I used to have.

If you have a separate focusser how about running the C11 focusser right to the end of its travel to make it more solid?

[ncjunk]

Unless you've done some physical damage to the mirror support I'd recommend running the mirror through the full travel of the focuser - this spreads the grease along the baffle. This should be done regularly.

You can verify the possible mirror movement by imaging then reversing the focusing direction - any movement you see will be the maximum "flop" during fast slewing.

I have a C9.25 and a C11 and have to say the mirror slop/ flop is significantly less than the Lx200's I was using.

Hi Merlin,

So take an image then move the mirror using the focus knob and refocus using the crayford and see how much movement there is?

Mr Spock,

I´ll give it a try but I am not sure I can achieve focus with the crayford if i set the mirror all the way back. At present I have the mirror set up so that the crayford focuses at it´s halfway point allowing maximum margin for focus corrections on the crayford.

thanks for the suggestions.

[ollypenrice]

The Meade that I have has a 'transit bolt' of the kind seen on new washing machines. It goes through the back of the scope and into the mirror cell. (Indeed this may be the thing that did the damage, if any were done, in the first place?) Astro Engineering exploit this feature to make a simple anti-flop gadget which I have and which might be copiable onto the C11, I don't know. A bolt passes through the back of the scope and threads into the cell in the same way the transit bolt threaded in. Over the bolt there is a long spring whch butts against a nut on the bolt. The idea is that the spring is compressed somewhat between the back of the scope and the nut, so the bolt permanently pulls back on the mirror cell.

If you too have a transit bolt hole in the cell than you might be able to use it in a similar way to pull the cell backwards all the time.

As I guess it gets pretty hot in your neck of the woods Ken's grease-stirring trick is likely to help, too.

Olly

[Merlin66]

Olly,

The Celestron focus mechanism is completely different from the Meade system.

The "Mirror Lock" screw has nowhere to locate and the mechanics of the adjusting screw would not "pull up"

99% of the slop is lack of grease distribution.

[ncjunk]

I have had a look online and saw the Meade system but the C11 is completely different.

My concern with the Grease is that my system is fully automated, in theory, but once set up if I get significant movement it ruins my pointing correction data. So, if moving the mirror redistributes the grease and reduces the mirror flop enough then the worry would be that in 6 months time I end up with a similar problem as the system, grease etc re-settle back to where they are now. I assume that the SCT design relies on the focusing of the main mirror using the knob to redistribute the grease?

I´m not sure this level of doubt is acceptable for me....I´ll just glue it down! :-D

Seriously though, I need to see if I can assure minimum mirror movement for my system or I´ll have to ditch the C11 but I am sure others use it the same way I am so perhaps mine is just a bit loose?

[Helen]

If you did decide to take the corrector off Neil I've got some high vacumm grease which is recommended for the regreasing.

Helen

[ncjunk]

Thanks Helen!

The EQ6 is looking good now and the roof is working great, just need to get the C11 settled or get another scope on and it´ll all be perfect.

[beamish]

I would have thought the trying the high vacuum grease has to be worth a try prior to thinking of selling. That should resolve a lot of the issues your seeing.

[ncjunk]

The mirror is set up quite a way towards the front, only 4 focuser rotations from full travel, would moving it inwards, as suggested by spock, make a difference? Is it more liable to move when positioned this far forward?

I didnt know scts could be so quirky!

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[Ransu]

I found last night that pointing was great around a localised area but when i slewed south a large distance it jumped the 2degrees.

It's not the mount as i have reverted back to gears so no possibility of slipping belts.

I recommend to double check dovetail holder and dec axis connection. I had to tighten this week my 3 CGEM screws, it shows similar error. pointing accuracy was ok in small area, but totally lost when in other side of sky. Screws had come loose and connection was sloppy.

I think so big error you have can not come from mirror slop

[ncjunk]

I recommend to double check dovetail holder and dec axis connection. I had to tighten this week my 3 CGEM screws, it shows similar error. pointing accuracy was ok in small area, but totally lost when in other side of sky. Screws had come loose and connection was sloppy.

I think so big error you have can not come from mirror slop

I have had loose screws as well so I think I will take the C11 off and do a re-grease (just found some guides online and it´s easier than the EQ6 that I´ve done) and while that is off re-fit the ed80 and check the mount out (if I still get a 2 degree shift its the mount).

I don´t think it is the mount as I have just reconfigred it again and put gears back on but I am still getting the same shift I have been all year. I would have expected the latest rebuild to have altered the amount of shift I was getting if it was the mechanical side of the mount.

[Peter Drew]

I've not taken a Celestron apart for some time so the mirror attachment may be different now. The mirrors used to be bonded on with a silicon type adhesive, a retaining sleeve held the mirror from the front. Your initial issue with the restraining screw could have forced the retaining sleeve forward causing a little clearance. If you do eventually dismantle the assembly for regreasing, which often is a good fix, it would be worth checking for this. Regarding how much inward of outward setting of the focal plane is concerned, it might be worth bearing in mind that extremes of focal position alters the design correction parameters.

[ncjunk]

Just an update

I mounted the ed80 back on and the pointing was back to how i expected errors in arc minutes so the object appeared only slightly off center.

My guiding error of a sudden jump of 20 pixels remained so is due to the mount shifting somehow. The peaks come in both directions so appears to be a movement that can go one way then resettle back the other.

Going to take the c11 apart next and see if its mirror flop can be reduced, if not it becomes useless to me but i am sure it can be fixed with a bit of double sided sticky tape and a bog roll.

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