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AVX sudden DEC drops (help.... help !)

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#1 betelgeuse91

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Posted 18 July 2019 - 11:21 AM

My AVX has sudden DEC drops like below... and it just makes me want to cry... 

 

I thought it could be the cables so I rearranged the cables but this repeatedly happens. 

 

I use backlash compensation for DEC via PHD2. 

The first picture shows normal operation. The backlash compensation overdrives the DEC just a bit but there is no problem. It settles down soon. 

 

However, the second picture shows when the DEC drops suddenly. DEC drops a lot and then goes through a huge backlash when it recovers. Interestingly, the sudden drops only happens in one direction all the time. Downwards like this, and huge backlash as it comes back. 

 

This has been bugging me for months and I tried leveling carefully, balancing carefully (although balancing with AVX is hard, I tried to have RA working against weight, DEC slightly heavy on one side), and tightening bolts carefully in order to avoid flexure... but this happens consistently. 

I even opened up the mount and regreased the gears, re-tightened the bolts on the warms and the motor but nothing helped... 

 

Please help... T__T

 

I put 80mm refractor with a dslr on AVX so reasonably light weight. Guiding equipment is 60mm guidescope with rings and QHY5L-ii-m guidecamera.

And here is the link for the PHD2 log from the most recent session. (which is typical for me)

 

Just one more question. With my current wide field setup, guiding error other than those drops doesn't bother me much. But do you think I can put a 6" f/6 Newtonian (14lbs) on it for imaging...?

Thanks so much for help..! 

 

 

 

 

normal operation 

cAsUXnK.png

 

 

 

sudden DEC drop

OLMCE05.png



#2 Jim Waters

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Posted 18 July 2019 - 11:28 AM

You should post the problem here too.  The AVX mount is NOT a good mount for imaging.

 

https://openphdguidi...g/getting-help/



#3 betelgeuse91

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Posted 18 July 2019 - 11:36 AM

You should post the problem here too.  The AVX mount is NOT a good mount for imaging.

 

https://openphdguidi...g/getting-help/

Thank you. I will post for help there as well...!

I know AVX is not the best but I started with a small budget... If I can fix this DEC drop issue, it should be good for wide field I think... 



#4 zxx

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Posted 18 July 2019 - 12:26 PM

Have you tried guiding Dec in one direction? I have the CGEM DX And must guide in one direction to get the best guiding.

 

Capture cgem.PNG


Edited by zxx, 18 July 2019 - 12:36 PM.


#5 betelgeuse91

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Posted 18 July 2019 - 12:37 PM

Have you tried guiding Dec in one direction? I have the CGEM DX And must guide in one direction to get the best guiding.

I have tried that but I found that I must guide in both directions because of DEC backlash during dithering and settling. The attached PHD2 log exactly shows this problem... 

 

By the way, that's some mind blowing guiding...


Edited by betelgeuse91, 18 July 2019 - 12:56 PM.


#6 zxx

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Posted 18 July 2019 - 12:56 PM

I believe guiding in one direction kinda acks like dithering. When I click through my lights I can see each one moves just a little.

You may get better results without dithering and guiding in one direction.

My exposures are 4 and 5 min and I don't see any field rotation guiding in one direction with my 6RC .

The trick to guide in one direction is PA, you don't want it spot on, I only use a polar scope.


Edited by zxx, 18 July 2019 - 01:41 PM.


#7 Astrojedi

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Posted 18 July 2019 - 02:35 PM

Does this drop in DEC repeat in consistent time intervals?



#8 betelgeuse91

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Posted 18 July 2019 - 03:56 PM

I believe guiding in one direction kinda acks like dithering. When I click through my lights I can see each one moves just a little.

You may get better results without dithering and guiding in one direction.

My exposures are 4 and 5 min and I don't see any field rotation guiding in one direction with my 6RC .

The trick to guide in one direction is PA, you don't want it spot on, I only use a polar scope.

I used to image that way and I got the fixed pattern noise so I give up on that way unfortunately... Maybe my Nikon d5300 picks up those kind of noise easier than your camera...

 

 

 

Does this drop in DEC repeat in consistent time intervals?

No but it seems rather random to me. But now it gets me to think that it could be some defeat among the gears which doesn't exhibit explicit periodicity... 



#9 zxx

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Posted 18 July 2019 - 04:19 PM

I used to image that way and I got the fixed pattern noise so I give up on that way unfortunately... Maybe my Nikon d5300 picks up those kind of noise easier than your camera...

 

 

 

No but it seems rather random to me. But now it gets me to think that it could be some defeat among the gears which doesn't exhibit explicit periodicity... 

My K50 also has the Sony cmos, but at 16mp 




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