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Fixed Mesu 200 first light - an old favourite

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Well I think I was the first gig on Lucas Mesu's UK tour.  He was doing a round robin to see the UK customers who'd been unfortunate enough to get mounts with a dodgy batch of RA motor/encoders.

It was really nice to get to chat about the mount with the designer.  He was clearly frustrated with the situation, but still just as enthusiastic about the merits of his design, and logic would certainly support this type of friction drive.

He was keen to explain that there will always be some level of 'ripple' on the PE, as the pin/rollers can never be completely perfect, but I took a couple of tracking plots first, and the was an obvious step change in performance from the old RA motor.   It's early days, but it certainly looks promising.  The only ripple I can see has an amplitude just under 0.5 arcsecs in 20s (42s full pin rotation period).

I'm new to off axis guiding, and still tweaking settings in PHD, plus the seeing wasn't great last night and there was a gusty wind.  In spite of this, I got a half decent shot of NGC891.


This is a sum of 10x15 min Atik 460 unbinned Lum subs, at about 1150mm (RC8 + CCDT67 at just under max spacing).  Lodestar OAG'd with 2s guide subs via PHD.

I know the stars aren't ultra round, and I have some field tilt/curve, but it's not a bad start.  Happy to see PGC9101 in the lower left, first time I've caught this in any kind of detail.

Shame I'm going away over the new moon - doh!

More soon,


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Hi Jack           just seen your post, can you please tell me what was wrong with the RA motor/encoders? I have a mesu 200 too, mine seems to track ok,  sometimes better than others, I found that the ra has to be balanced quite well to get good tracking

Nice image!...   Regards Rick

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If it appears to track ok then you needn't worry.

Lucas built a run of mounts with faulhaber servos and magnetic encoders. Some of these motors/encoders had flaws which caused a severe ripple during tracking.

Check out the Mesu guiding topic by pubquiz and you'll see the dodgy plots. You couldn't miss it if you had one like this.

Mine is night and day different now. Just need more clear nights.


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My Mesu 200 wasn't one of the small number with the different motor but I spent a very enjoyable afternoon with Lucas while he was over here. We had a great chat about the design and his plans for the future  - all great stuff!

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Yes, the stars are not quite there yet. There is a slight elongation running NE/SW as presented and there are dark haloes around the smaller ones. This usually comes from Deconvolution. I tend to exclude stars from any sharpening routines.

The standard test is to do a short 5 second sub on some brightish stars. This will eliminate the mount as the culprit if the distortions persist. I'm assuming this was with the RC8?

On the other hand it might just be the wind.


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Guys, many thanks for all the feedback.

Yves, I don't think I have the mount working perfectly yet by any means, but having seen the dec guiding trace which was poor and an RA trace which looked really smooth, I'm hoping I can improve the overall tracking with sitech and phd settings and maybe a rebalance.

Olly, you're right about the deconvolution artefacts. I only had 30 mins to calibrate, register and integrate this data before going on holiday an normally would have waited to post, but what can I say, I was in a hurry to share it. I know almost nothing about processing, and saw some improvement in the galaxy from a default deconvolve and some stars are ok. But now I can see the bigger stars have darker centres and the small ones have dark circles around them.

Thinking logically about this, it now seems obvious that the reason I have some round stars in the image, is because in some areas field tilt is elongating them in one direction and tracking errors (dec I think) are elongating them at right angles to the tilt. So they are round, but bigger than they ought to be.

And Steve, yes we all know you're an astrophotography VIP over here, and you did write the mesu 200 review, so Lucas was bound to come and see you to get your feedback first hand. I found he came across as a very decent chap, although I surprised him because he thought I would be a retired gentleman - I must write emails and forum posts like an old man!

Is 43 old? Don't answer that. I am retiring I suppose,, but only from the air force, i'll certainly still need to work for a while yet.


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