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M81


KevS

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Posted by: @KevS

M81 evenings of 25th and 26th January 2021. 173 x 180s, ISO800 + Darks/Flats/Bias, Canon 600d (Non-Mod), 152 f5.9 TS, IR/UV cut off. Stacked in DSS and manipulated in GIMP. Bit rough and ready but first image for months. 

Looking great. You are the envy of everyone on here, nobody else is doing much at all.

Brian

 

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Posted by: @MarkAR

Nice one Kev, all you need now is to sort out the walking noise.

Thanks Mark, I was dithering but obviously not enough. The new PHD2 2 star guiding is playing havoc with the mount's auxiliary "built in dither" ? May have to increase the dither used via APT. 

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I rebuilt the mount some time ago, replacing the bearings and the snot that passes as grease from Skywatcher. I get 0.2"-0.3" RMS as a result. Replacing the bearings also improved the orthoganality of the mount no end. I used to get better results with regarding to "walking noise" previous to the rebuild due to the inbuilt errors in the drive system. Improving the mechanicals on the mount has certainly improved tracking, but has brought out the  previously mentioned walking noise. I am still subject to a certain amount of field rotation as I set up from scratch and  I can not normally get closer than about 4-5 arc minutes. If we ever get a run of clear nights again I will have to experiment with the dither settings and see if I can dial it out. 

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On 2/4/2021 at 2:20 PM, KevS said:

I rebuilt the mount some time ago, replacing the bearings and the snot that passes as grease from Skywatcher. I get 0.2"-0.3" RMS as a result. Replacing the bearings also improved the orthoganality of the mount no end. I used to get better results with regarding to "walking noise" previous to the rebuild due to the inbuilt errors in the drive system. Improving the mechanicals on the mount has certainly improved tracking, but has brought out the  previously mentioned walking noise. I am still subject to a certain amount of field rotation as I set up from scratch and  I can not normally get closer than about 4-5 arc minutes. If we ever get a run of clear nights again I will have to experiment with the dither settings and see if I can dial it out. 

 

What grease did you use? I used teflon grease on an EQ3 with success but clearly whatever you used has worked!

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I used PTFE/Moly grease that I use for my bike wheels, the  bearings I replaced were the most important factor, I used "P4" class SKF class bearings. (Taper needle bearings) I wanted to use P5's ( traceable) but they would have cost more than the mount. Fortunately the P4 class sets were readily available "free" from contacts within industry. There appeared to be some spalling on the mount castings due to possible movement/vibration of the original outer races, as a consequence "641" bearing lock was used to assist location after the inner castings were "popped". End float/preload was achieved using a digital DTI allowing for the stretch in both Dec and Ra shafts. 

 

The following may be of use.

 

Principles of bearing selection and application | SKF | SKF

 

K

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